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verilator/src/V3DfgAstToDfg.cpp

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Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// -*- mode: C++; c-file-style: "cc-mode" -*-
//*************************************************************************
// DESCRIPTION: Verilator: Convert AstModule to DfgGraph
//
// Code available from: https://verilator.org
//
//*************************************************************************
//
Copyright year update
2023-01-01 16:18:39 +01:00
// Copyright 2003-2023 by Wilson Snyder. This program is free software; you
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// can redistribute it and/or modify it under the terms of either the GNU
// Lesser General Public License Version 3 or the Perl Artistic License
// Version 2.0.
// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
//
//*************************************************************************
//
Fix spelling
2023-11-11 05:25:53 +01:00
// Convert and AstModule to a DfgGraph. We proceed by visiting convertible logic blocks (e.g.:
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// AstAssignW of appropriate type and with no delays), recursively constructing DfgVertex instances
// for the expressions that compose the subject logic block. If all expressions in the current
// logic block can be converted, then we delete the logic block (now represented in the DfgGraph),
// and connect the corresponding DfgVertex instances appropriately. If some of the expressions were
// not convertible in the current logic block, we revert (delete) the DfgVertex instances created
// for the logic block, and leave the logic block in the AstModule. Any variable reference from
// non-converted logic blocks (or other constructs under the AstModule) are marked as being
// referenced in the AstModule, which is relevant for later optimization.
//
//*************************************************************************
Fix header order botched by clang-format in recent commit.
2023-10-18 12:37:46 +02:00
#include "V3PchAstNoMT.h" // VL_MT_DISABLED_CODE_UNIT
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
#include "V3Dfg.h"
#include "V3DfgPasses.h"
VL_DEFINE_DEBUG_FUNCTIONS;
namespace {
Make all expressions derive from AstNodeExpr (#3721). Apart from the representational changes below, this patch renames AstNodeMath to AstNodeExpr, and AstCMath to AstCExpr. Now every expression (i.e.: those AstNodes that represent a [possibly void] value, with value being interpreted in a very general sense) has AstNodeExpr as a super class. This necessitates the introduction of an AstStmtExpr, which represents an expression in statement position, e.g : 'foo();' would be represented as AstStmtExpr(AstCCall(foo)). In exchange we can get rid of isStatement() in AstNodeStmt, which now really always represent a statement Peak memory consumption and verilation speed are not measurably changed. Partial step towards #3420
2022-10-12 11:19:21 +02:00
// Create a DfgVertex out of a AstNodeExpr. For most AstNodeExpr subtypes, this can be done
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// automatically. For the few special cases, we provide specializations below
DFG: Make implementation more similar to AST Use the same style, and reuse the bulk of astgen to generate DfgVertex related code. In particular allow for easier definition of custom DfgVertex sub-types that do not directly correspond to an AstNode sub-type. Also introduces specific names for the fixed arity vertices. No functional change intended.
2022-10-04 12:03:41 +02:00
template <typename Vertex, typename Node>
Vertex* makeVertex(const Node* nodep, DfgGraph& dfg) {
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
return new Vertex{dfg, nodep->fileline(), DfgVertex::dtypeFor(nodep)};
}
//======================================================================
// Currently unhandled nodes
// LCOV_EXCL_START
// AstCCast changes width, but should not exists where DFG optimization is currently invoked
template <>
DFG: Make implementation more similar to AST Use the same style, and reuse the bulk of astgen to generate DfgVertex related code. In particular allow for easier definition of custom DfgVertex sub-types that do not directly correspond to an AstNode sub-type. Also introduces specific names for the fixed arity vertices. No functional change intended.
2022-10-04 12:03:41 +02:00
DfgCCast* makeVertex<DfgCCast, AstCCast>(const AstCCast*, DfgGraph&) {
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
return nullptr;
}
// Unhandled in DfgToAst, but also operates on strings which we don't optimize anyway
template <>
DFG: Make implementation more similar to AST Use the same style, and reuse the bulk of astgen to generate DfgVertex related code. In particular allow for easier definition of custom DfgVertex sub-types that do not directly correspond to an AstNode sub-type. Also introduces specific names for the fixed arity vertices. No functional change intended.
2022-10-04 12:03:41 +02:00
DfgAtoN* makeVertex<DfgAtoN, AstAtoN>(const AstAtoN*, DfgGraph&) {
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
return nullptr;
}
// Unhandled in DfgToAst, but also operates on strings which we don't optimize anyway
template <>
DFG: Make implementation more similar to AST Use the same style, and reuse the bulk of astgen to generate DfgVertex related code. In particular allow for easier definition of custom DfgVertex sub-types that do not directly correspond to an AstNode sub-type. Also introduces specific names for the fixed arity vertices. No functional change intended.
2022-10-04 12:03:41 +02:00
DfgCompareNN* makeVertex<DfgCompareNN, AstCompareNN>(const AstCompareNN*, DfgGraph&) {
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
return nullptr;
}
// Unhandled in DfgToAst, but also operates on unpacked arrays which we don't optimize anyway
template <>
DFG: Make implementation more similar to AST Use the same style, and reuse the bulk of astgen to generate DfgVertex related code. In particular allow for easier definition of custom DfgVertex sub-types that do not directly correspond to an AstNode sub-type. Also introduces specific names for the fixed arity vertices. No functional change intended.
2022-10-04 12:03:41 +02:00
DfgSliceSel* makeVertex<DfgSliceSel, AstSliceSel>(const AstSliceSel*, DfgGraph&) {
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
return nullptr;
}
// LCOV_EXCL_STOP
} // namespace
class AstToDfgVisitor final : public VNVisitor {
// NODE STATE
// AstNode::user1p // DfgVertex for this AstNode
const VNUser1InUse m_user1InUse;
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
// TYPES
// Represents a driver during canonicalization
struct Driver {
FileLine* m_fileline;
DfgVertex* m_vtxp;
uint32_t m_lsb;
Driver(FileLine* flp, uint32_t lsb, DfgVertex* vtxp)
: m_fileline{flp}
, m_vtxp{vtxp}
, m_lsb{lsb} {}
};
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// STATE
DfgGraph* const m_dfgp; // The graph being built
V3DfgOptimizationContext& m_ctx; // The optimization context for stats
bool m_foundUnhandled = false; // Found node not implemented as DFG or not implemented 'visit'
std::vector<DfgVertex*> m_uncommittedVertices; // Vertices that we might decide to revert
Ensure DFG stats are consistent
2022-09-26 15:21:05 +02:00
bool m_converting = false; // We are trying to convert some logic at the moment
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
std::vector<DfgVarPacked*> m_varPackedps; // All the DfgVarPacked vertices we created.
std::vector<DfgVarArray*> m_varArrayps; // All the DfgVarArray vertices we created.
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// METHODS
void markReferenced(AstNode* nodep) {
Improve V3Ast function usage ergonomics (#3650) Signed-off-by: HungMingWu <u9089000@gmail.com>
2022-10-20 14:48:44 +02:00
nodep->foreach([this](const AstVarRef* refp) {
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// No need to (and in fact cannot) mark variables with unsupported dtypes
if (!DfgVertex::isSupportedDType(refp->varp()->dtypep())) return;
Dfg: Fix crash on additional driver from non-DFG logic Ensure variables written by non-DFG code are kept Fixes #3740
2022-11-12 12:35:23 +01:00
// Mark vertex as having a module reference outside current DFG
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
getNet(refp->varp())->setHasModRefs();
Dfg: Fix crash on additional driver from non-DFG logic Ensure variables written by non-DFG code are kept Fixes #3740
2022-11-12 12:35:23 +01:00
// Mark variable as written from non-DFG logic
if (refp->access().isWriteOrRW()) refp->varp()->user3(true);
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
});
}
void commitVertices() { m_uncommittedVertices.clear(); }
void revertUncommittedVertices() {
for (DfgVertex* const vtxp : m_uncommittedVertices) vtxp->unlinkDelete(*m_dfgp);
m_uncommittedVertices.clear();
}
DFG: Make implementation more similar to AST Use the same style, and reuse the bulk of astgen to generate DfgVertex related code. In particular allow for easier definition of custom DfgVertex sub-types that do not directly correspond to an AstNode sub-type. Also introduces specific names for the fixed arity vertices. No functional change intended.
2022-10-04 12:03:41 +02:00
DfgVertexVar* getNet(AstVar* varp) {
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
if (!varp->user1p()) {
DFG: Make implementation more similar to AST Use the same style, and reuse the bulk of astgen to generate DfgVertex related code. In particular allow for easier definition of custom DfgVertex sub-types that do not directly correspond to an AstNode sub-type. Also introduces specific names for the fixed arity vertices. No functional change intended.
2022-10-04 12:03:41 +02:00
// Note DfgVertexVar vertices are not added to m_uncommittedVertices, because we
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
// want to hold onto them via AstVar::user1p, and the AstVar might be referenced via
DFG: Make implementation more similar to AST Use the same style, and reuse the bulk of astgen to generate DfgVertex related code. In particular allow for easier definition of custom DfgVertex sub-types that do not directly correspond to an AstNode sub-type. Also introduces specific names for the fixed arity vertices. No functional change intended.
2022-10-04 12:03:41 +02:00
// multiple AstVarRef instances, so we will never revert a DfgVertexVar once
DFG: Remove unconneced variables early
2022-09-30 12:35:03 +02:00
// created. We will delete unconnected variable vertices at the end.
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
if (VN_IS(varp->dtypep()->skipRefp(), UnpackArrayDType)) {
DfgVarArray* const vtxp = new DfgVarArray{*m_dfgp, varp};
varp->user1p();
m_varArrayps.push_back(vtxp);
varp->user1p(vtxp);
} else {
DfgVarPacked* const vtxp = new DfgVarPacked{*m_dfgp, varp};
m_varPackedps.push_back(vtxp);
varp->user1p(vtxp);
}
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
}
DFG: Make implementation more similar to AST Use the same style, and reuse the bulk of astgen to generate DfgVertex related code. In particular allow for easier definition of custom DfgVertex sub-types that do not directly correspond to an AstNode sub-type. Also introduces specific names for the fixed arity vertices. No functional change intended.
2022-10-04 12:03:41 +02:00
return varp->user1u().to<DfgVertexVar*>();
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
}
DfgVertex* getVertex(AstNode* nodep) {
DfgVertex* vtxp = nodep->user1u().to<DfgVertex*>();
UASSERT_OBJ(vtxp, nodep, "Missing Dfg vertex");
return vtxp;
}
// Returns true if the expression cannot (or should not) be represented by DFG
Make all expressions derive from AstNodeExpr (#3721). Apart from the representational changes below, this patch renames AstNodeMath to AstNodeExpr, and AstCMath to AstCExpr. Now every expression (i.e.: those AstNodes that represent a [possibly void] value, with value being interpreted in a very general sense) has AstNodeExpr as a super class. This necessitates the introduction of an AstStmtExpr, which represents an expression in statement position, e.g : 'foo();' would be represented as AstStmtExpr(AstCCall(foo)). In exchange we can get rid of isStatement() in AstNodeStmt, which now really always represent a statement Peak memory consumption and verilation speed are not measurably changed. Partial step towards #3420
2022-10-12 11:19:21 +02:00
bool unhandled(AstNodeExpr* nodep) {
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// Short-circuiting if something was already unhandled
if (!m_foundUnhandled) {
// Impure nodes cannot be represented
if (!nodep->isPure()) {
m_foundUnhandled = true;
++m_ctx.m_nonRepImpure;
}
// Check node has supported dtype
if (!DfgVertex::isSupportedDType(nodep->dtypep())) {
m_foundUnhandled = true;
++m_ctx.m_nonRepDType;
}
}
return m_foundUnhandled;
}
DFG: Support AstSel and AstConcat on LHS of assignments Added DfgVertexVariadic to represent DFG vetices with a varying number of source operands. Converted DfgVar to be a variadic vertex, with each driver corresponding to a fixed range of bits in the packed variable. This allows us to handle AstSel on the LHS of assignments. Also added support for AstConcat on the LHS by selecting into the RHS as appropriate. This improves OpenTitan ST speed by ~13%
2022-09-25 17:03:15 +02:00
// Build DfgEdge representing the LValue assignment. Returns false if unsuccessful.
bool convertAssignment(FileLine* flp, AstNode* nodep, DfgVertex* vtxp) {
if (AstVarRef* const vrefp = VN_CAST(nodep, VarRef)) {
m_foundUnhandled = false;
visit(vrefp);
if (m_foundUnhandled) return false;
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
getVertex(vrefp)->as<DfgVarPacked>()->addDriver(flp, 0, vtxp);
DFG: Support AstSel and AstConcat on LHS of assignments Added DfgVertexVariadic to represent DFG vetices with a varying number of source operands. Converted DfgVar to be a variadic vertex, with each driver corresponding to a fixed range of bits in the packed variable. This allows us to handle AstSel on the LHS of assignments. Also added support for AstConcat on the LHS by selecting into the RHS as appropriate. This improves OpenTitan ST speed by ~13%
2022-09-25 17:03:15 +02:00
return true;
}
if (AstSel* const selp = VN_CAST(nodep, Sel)) {
AstVarRef* const vrefp = VN_CAST(selp->fromp(), VarRef);
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
const AstConst* const lsbp = VN_CAST(selp->lsbp(), Const);
DFG: Support AstSel and AstConcat on LHS of assignments Added DfgVertexVariadic to represent DFG vetices with a varying number of source operands. Converted DfgVar to be a variadic vertex, with each driver corresponding to a fixed range of bits in the packed variable. This allows us to handle AstSel on the LHS of assignments. Also added support for AstConcat on the LHS by selecting into the RHS as appropriate. This improves OpenTitan ST speed by ~13%
2022-09-25 17:03:15 +02:00
if (!vrefp || !lsbp || !VN_IS(selp->widthp(), Const)) {
++m_ctx.m_nonRepLhs;
return false;
}
m_foundUnhandled = false;
visit(vrefp);
if (m_foundUnhandled) return false;
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
getVertex(vrefp)->as<DfgVarPacked>()->addDriver(flp, lsbp->toUInt(), vtxp);
return true;
}
if (AstArraySel* const selp = VN_CAST(nodep, ArraySel)) {
AstVarRef* const vrefp = VN_CAST(selp->fromp(), VarRef);
const AstConst* const idxp = VN_CAST(selp->bitp(), Const);
if (!vrefp || !idxp) {
++m_ctx.m_nonRepLhs;
return false;
}
m_foundUnhandled = false;
visit(vrefp);
if (m_foundUnhandled) return false;
getVertex(vrefp)->as<DfgVarArray>()->addDriver(flp, idxp->toUInt(), vtxp);
DFG: Support AstSel and AstConcat on LHS of assignments Added DfgVertexVariadic to represent DFG vetices with a varying number of source operands. Converted DfgVar to be a variadic vertex, with each driver corresponding to a fixed range of bits in the packed variable. This allows us to handle AstSel on the LHS of assignments. Also added support for AstConcat on the LHS by selecting into the RHS as appropriate. This improves OpenTitan ST speed by ~13%
2022-09-25 17:03:15 +02:00
return true;
}
if (AstConcat* const concatp = VN_CAST(nodep, Concat)) {
AstNode* const lhsp = concatp->lhsp();
AstNode* const rhsp = concatp->rhsp();
{
FileLine* const lFlp = lhsp->fileline();
DfgSel* const lVtxp = new DfgSel{*m_dfgp, lFlp, DfgVertex::dtypeFor(lhsp)};
lVtxp->fromp(vtxp);
DFG: Special case representation of AstSel AstSel is a ternary node, but the 'widthp' is always constant and is hence redundant, and 'lsbp' is very often constant. As AstSel is fairly common, we special case as a DfgSel for the constant 'lsbp', and as 'DfgMux` for the non-constant 'lsbp'.
2022-10-06 19:34:18 +02:00
lVtxp->lsb(rhsp->width());
DFG: Support AstSel and AstConcat on LHS of assignments Added DfgVertexVariadic to represent DFG vetices with a varying number of source operands. Converted DfgVar to be a variadic vertex, with each driver corresponding to a fixed range of bits in the packed variable. This allows us to handle AstSel on the LHS of assignments. Also added support for AstConcat on the LHS by selecting into the RHS as appropriate. This improves OpenTitan ST speed by ~13%
2022-09-25 17:03:15 +02:00
if (!convertAssignment(flp, lhsp, lVtxp)) return false;
}
{
FileLine* const rFlp = rhsp->fileline();
DfgSel* const rVtxp = new DfgSel{*m_dfgp, rFlp, DfgVertex::dtypeFor(rhsp)};
rVtxp->fromp(vtxp);
DFG: Special case representation of AstSel AstSel is a ternary node, but the 'widthp' is always constant and is hence redundant, and 'lsbp' is very often constant. As AstSel is fairly common, we special case as a DfgSel for the constant 'lsbp', and as 'DfgMux` for the non-constant 'lsbp'.
2022-10-06 19:34:18 +02:00
rVtxp->lsb(0);
DFG: Support AstSel and AstConcat on LHS of assignments Added DfgVertexVariadic to represent DFG vetices with a varying number of source operands. Converted DfgVar to be a variadic vertex, with each driver corresponding to a fixed range of bits in the packed variable. This allows us to handle AstSel on the LHS of assignments. Also added support for AstConcat on the LHS by selecting into the RHS as appropriate. This improves OpenTitan ST speed by ~13%
2022-09-25 17:03:15 +02:00
return convertAssignment(flp, rhsp, rVtxp);
}
}
++m_ctx.m_nonRepLhs;
return false;
}
DFG: handle simple always blocks
2022-10-01 13:28:16 +02:00
bool convertEquation(AstNode* nodep, FileLine* flp, AstNode* lhsp, AstNode* rhsp) {
DFG: Support AstSel and AstConcat on LHS of assignments Added DfgVertexVariadic to represent DFG vetices with a varying number of source operands. Converted DfgVar to be a variadic vertex, with each driver corresponding to a fixed range of bits in the packed variable. This allows us to handle AstSel on the LHS of assignments. Also added support for AstConcat on the LHS by selecting into the RHS as appropriate. This improves OpenTitan ST speed by ~13%
2022-09-25 17:03:15 +02:00
UASSERT_OBJ(m_uncommittedVertices.empty(), nodep, "Should not nest");
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
// Currently cannot handle direct assignments between unpacked types. These arise e.g.
// when passing an unpacked array through a module port.
if (!DfgVertex::isSupportedPackedDType(lhsp->dtypep())
|| !DfgVertex::isSupportedPackedDType(rhsp->dtypep())) {
markReferenced(nodep);
++m_ctx.m_nonRepDType;
return false;
}
DFG: Support AstSel and AstConcat on LHS of assignments Added DfgVertexVariadic to represent DFG vetices with a varying number of source operands. Converted DfgVar to be a variadic vertex, with each driver corresponding to a fixed range of bits in the packed variable. This allows us to handle AstSel on the LHS of assignments. Also added support for AstConcat on the LHS by selecting into the RHS as appropriate. This improves OpenTitan ST speed by ~13%
2022-09-25 17:03:15 +02:00
// Cannot handle mismatched widths. Mismatched assignments should have been fixed up in
// earlier passes anyway, so this should never be hit, but being paranoid just in case.
if (lhsp->width() != rhsp->width()) { // LCOV_EXCL_START
markReferenced(nodep);
++m_ctx.m_nonRepWidth;
return false;
} // LCOV_EXCL_STOP
VL_RESTORER(m_converting);
m_converting = true;
m_foundUnhandled = false;
iterate(rhsp);
if (m_foundUnhandled) {
revertUncommittedVertices();
markReferenced(nodep);
return false;
}
DFG: handle simple always blocks
2022-10-01 13:28:16 +02:00
if (!convertAssignment(flp, lhsp, getVertex(rhsp))) {
DFG: Support AstSel and AstConcat on LHS of assignments Added DfgVertexVariadic to represent DFG vetices with a varying number of source operands. Converted DfgVar to be a variadic vertex, with each driver corresponding to a fixed range of bits in the packed variable. This allows us to handle AstSel on the LHS of assignments. Also added support for AstConcat on the LHS by selecting into the RHS as appropriate. This improves OpenTitan ST speed by ~13%
2022-09-25 17:03:15 +02:00
revertUncommittedVertices();
markReferenced(nodep);
return false;
}
// Connect the rhs vertex to the driven edge
commitVertices();
// Remove node from Ast. Now represented by the Dfg.
VL_DO_DANGLING(nodep->unlinkFrBack()->deleteTree(), nodep);
//
++m_ctx.m_representable;
return true;
}
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
// Sometime assignment ranges are coalesced by V3Const,
// so we unpack concatenations for better error reporting.
void addDriver(FileLine* flp, uint32_t lsb, DfgVertex* vtxp,
std::vector<Driver>& drivers) const {
if (DfgConcat* const concatp = vtxp->cast<DfgConcat>()) {
DfgVertex* const rhsp = concatp->rhsp();
Fix crash in DFT due to width use after free (#3817) (#3820)
2022-12-21 01:36:04 +01:00
auto const rhs_width = rhsp->width();
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
addDriver(rhsp->fileline(), lsb, rhsp, drivers);
DfgVertex* const lhsp = concatp->lhsp();
Fix crash in DFT due to width use after free (#3817) (#3820)
2022-12-21 01:36:04 +01:00
addDriver(lhsp->fileline(), lsb + rhs_width, lhsp, drivers);
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
concatp->unlinkDelete(*m_dfgp);
} else {
drivers.emplace_back(flp, lsb, vtxp);
}
}
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
// Canonicalize packed variables
void canonicalizePacked() {
for (DfgVarPacked* const varp : m_varPackedps) {
DFG: Remove unconneced variables early
2022-09-30 12:35:03 +02:00
// Delete variables with no sinks nor sources (this can happen due to reverting
// uncommitted vertices, which does not remove variables)
if (!varp->hasSinks() && varp->arity() == 0) {
VL_DO_DANGLING(varp->unlinkDelete(*m_dfgp), varp);
continue;
}
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
// Gather (and unlink) all drivers
std::vector<Driver> drivers;
drivers.reserve(varp->arity());
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
varp->forEachSourceEdge([this, varp, &drivers](DfgEdge& edge, size_t idx) {
DfgVertex* const driverp = edge.sourcep();
UASSERT(driverp, "Should not have created undriven sources");
addDriver(varp->driverFileLine(idx), varp->driverLsb(idx), driverp, drivers);
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
edge.unlinkSource();
});
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
const auto cmp = [](const Driver& a, const Driver& b) {
if (a.m_lsb != b.m_lsb) return a.m_lsb < b.m_lsb;
return a.m_fileline->operatorCompare(*b.m_fileline) < 0;
};
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
// Sort drivers by LSB
std::stable_sort(drivers.begin(), drivers.end(), cmp);
// Vertices that might have become unused due to multiple driver resolution. Having
// multiple drivers is an error and is hence assumed to be rare, so performance is
// not very important, set will suffice.
std::set<DfgVertex*> prune;
// Fix multiply driven ranges
for (auto it = drivers.begin(); it != drivers.end();) {
Driver& a = *it++;
const uint32_t aWidth = a.m_vtxp->width();
const uint32_t aEnd = a.m_lsb + aWidth;
while (it != drivers.end()) {
Driver& b = *it;
// If no overlap, then nothing to do
if (b.m_lsb >= aEnd) break;
const uint32_t bWidth = b.m_vtxp->width();
const uint32_t bEnd = b.m_lsb + bWidth;
const uint32_t overlapEnd = std::min(aEnd, bEnd) - 1;
Fix incorrect multi-driven lint warning (#4231) (#4248)
2023-06-01 14:43:17 +02:00
if (a.m_fileline->operatorCompare(*b.m_fileline) != 0) {
varp->varp()->v3warn( //
MULTIDRIVEN,
"Bits [" //
<< overlapEnd << ":" << b.m_lsb << "] of signal "
<< varp->varp()->prettyNameQ()
<< " have multiple combinational drivers\n"
<< a.m_fileline->warnOther() << "... Location of first driver\n"
<< a.m_fileline->warnContextPrimary() << '\n'
<< b.m_fileline->warnOther() << "... Location of other driver\n"
<< b.m_fileline->warnContextSecondary()
<< varp->varp()->warnOther()
<< "... Only the first driver will be respected");
}
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
// If the first driver completely covers the range of the second driver,
// we can just delete the second driver completely, otherwise adjust the
// second driver to apply from the end of the range of the first driver.
if (aEnd >= bEnd) {
prune.emplace(b.m_vtxp);
it = drivers.erase(it);
} else {
const auto dtypep = DfgVertex::dtypeForWidth(bEnd - aEnd);
DfgSel* const selp = new DfgSel{*m_dfgp, b.m_vtxp->fileline(), dtypep};
selp->fromp(b.m_vtxp);
selp->lsb(aEnd - b.m_lsb);
b.m_lsb = aEnd;
b.m_vtxp = selp;
std::stable_sort(it, drivers.end(), cmp);
}
}
}
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
// Coalesce adjacent ranges
for (size_t i = 0, j = 1; j < drivers.size(); ++j) {
Driver& a = drivers[i];
Driver& b = drivers[j];
// Coalesce adjacent range
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
const uint32_t aWidth = a.m_vtxp->width();
const uint32_t bWidth = b.m_vtxp->width();
if (a.m_lsb + aWidth == b.m_lsb) {
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
const auto dtypep = DfgVertex::dtypeForWidth(aWidth + bWidth);
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
DfgConcat* const concatp = new DfgConcat{*m_dfgp, a.m_fileline, dtypep};
concatp->rhsp(a.m_vtxp);
concatp->lhsp(b.m_vtxp);
a.m_vtxp = concatp;
b.m_vtxp = nullptr; // Mark as moved
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
++m_ctx.m_coalescedAssignments;
continue;
}
++i;
// Compact non-adjacent ranges within the vector
if (j != i) {
Driver& c = drivers[i];
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
UASSERT_OBJ(!c.m_vtxp, c.m_fileline, "Should have been marked moved");
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
c = b;
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
b.m_vtxp = nullptr; // Mark as moved
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
}
}
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
// Reinsert drivers in order
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
varp->resetSources();
for (const Driver& driver : drivers) {
Dfg: resolve multi-driven signal ranges In order to avoid unexpected breakage on multi-driven variables, we resolve in DFG construction by using only the first driver encountered. Also issues the MULTIDRIVEN error for these signals.
2022-11-12 15:14:32 +01:00
if (!driver.m_vtxp) break; // Stop at end of compacted list
varp->addDriver(driver.m_fileline, driver.m_lsb, driver.m_vtxp);
}
// Prune vertices potentially unused due to resolving multiple drivers.
while (!prune.empty()) {
// Pop last vertex
const auto it = prune.begin();
DfgVertex* const vtxp = *it;
prune.erase(it);
// If used (or a variable), then done
if (vtxp->hasSinks() || vtxp->is<DfgVertexVar>()) continue;
// If unused, then add sources to work list and delete
vtxp->forEachSource([&](DfgVertex& src) { prune.emplace(&src); });
vtxp->unlinkDelete(*m_dfgp);
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
}
}
}
DFG: Remove unconneced variables early
2022-09-30 12:35:03 +02:00
// Canonicalize array variables
void canonicalizeArray() {
for (DfgVarArray* const varp : m_varArrayps) {
// Delete variables with no sinks nor sources (this can happen due to reverting
// uncommitted vertices, which does not remove variables)
if (!varp->hasSinks() && varp->arity() == 0) {
VL_DO_DANGLING(varp->unlinkDelete(*m_dfgp), varp);
}
}
}
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// VISITORS
void visit(AstNode* nodep) override {
// Conservatively treat this node as unhandled
Ensure DFG stats are consistent
2022-09-26 15:21:05 +02:00
if (!m_foundUnhandled && m_converting) ++m_ctx.m_nonRepUnknown;
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
m_foundUnhandled = true;
markReferenced(nodep);
}
void visit(AstCell* nodep) override { markReferenced(nodep); }
void visit(AstNodeProcedure* nodep) override { markReferenced(nodep); }
void visit(AstVar* nodep) override {
Fix SystemC signal copy macro use (#4135).
2023-05-27 13:00:26 +02:00
if (nodep->isSc()) return;
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// No need to (and in fact cannot) handle variables with unsupported dtypes
if (!DfgVertex::isSupportedDType(nodep->dtypep())) return;
// Mark ports as having external references
if (nodep->isIO()) getNet(nodep)->setHasExtRefs();
// Mark variables that are the target of a hierarchical reference
// (these flags were set up in DataflowPrepVisitor)
if (nodep->user2()) getNet(nodep)->setHasExtRefs();
}
void visit(AstAssignW* nodep) override {
Ensure DFG stats are consistent
2022-09-26 15:21:05 +02:00
++m_ctx.m_inputEquations;
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
// Cannot handle assignment with timing control yet
if (nodep->timingControlp()) {
markReferenced(nodep);
++m_ctx.m_nonRepTiming;
return;
}
DFG: handle simple always blocks
2022-10-01 13:28:16 +02:00
convertEquation(nodep, nodep->fileline(), nodep->lhsp(), nodep->rhsp());
}
void visit(AstAlways* nodep) override {
// Ignore sequential logic, or if there are multiple statements
const VAlwaysKwd kwd = nodep->keyword();
if (nodep->sensesp() || !nodep->isJustOneBodyStmt()
|| (kwd != VAlwaysKwd::ALWAYS && kwd != VAlwaysKwd::ALWAYS_COMB)) {
markReferenced(nodep);
return;
}
AstNode* const stmtp = nodep->stmtsp();
if (AstAssign* const assignp = VN_CAST(stmtp, Assign)) {
++m_ctx.m_inputEquations;
if (assignp->timingControlp()) {
markReferenced(stmtp);
++m_ctx.m_nonRepTiming;
return;
}
convertEquation(nodep, assignp->fileline(), assignp->lhsp(), assignp->rhsp());
} else if (AstIf* const ifp = VN_CAST(stmtp, If)) {
// Will only handle single assignments to the same LHS in both branches
AstAssign* const thenp = VN_CAST(ifp->thensp(), Assign);
AstAssign* const elsep = VN_CAST(ifp->elsesp(), Assign);
if (!thenp || !elsep || thenp->nextp() || elsep->nextp()
|| !thenp->lhsp()->sameTree(elsep->lhsp())) {
markReferenced(stmtp);
return;
}
++m_ctx.m_inputEquations;
if (thenp->timingControlp() || elsep->timingControlp()) {
markReferenced(stmtp);
++m_ctx.m_nonRepTiming;
return;
}
// Create a conditional for the rhs by borrowing the components from the AstIf
AstCond* const rhsp = new AstCond{ifp->fileline(), //
ifp->condp()->unlinkFrBack(), //
thenp->rhsp()->unlinkFrBack(), //
elsep->rhsp()->unlinkFrBack()};
if (!convertEquation(nodep, ifp->fileline(), thenp->lhsp(), rhsp)) {
// Failed to convert. Mark 'rhsp', as 'convertEquation' only marks 'nodep'.
markReferenced(rhsp);
// Put the AstIf back together
ifp->condp(rhsp->condp()->unlinkFrBack());
thenp->rhsp(rhsp->thenp()->unlinkFrBack());
elsep->rhsp(rhsp->elsep()->unlinkFrBack());
}
// Delete the auxiliary conditional
VL_DO_DANGLING(rhsp->deleteTree(), rhsp);
} else {
markReferenced(stmtp);
}
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
}
void visit(AstVarRef* nodep) override {
UASSERT_OBJ(!nodep->user1p(), nodep, "Already has Dfg vertex");
if (unhandled(nodep)) return;
if (nodep->access().isRW() // Cannot represent read-write references
|| nodep->varp()->isIfaceRef() // Cannot handle interface references
|| nodep->varp()->delayp() // Cannot handle delayed variables
|| nodep->classOrPackagep() // Cannot represent cross module references
) {
markReferenced(nodep);
m_foundUnhandled = true;
++m_ctx.m_nonRepVarRef;
return;
}
// Sadly sometimes AstVarRef does not have the same dtype as the referenced variable
if (!DfgVertex::isSupportedDType(nodep->varp()->dtypep())) {
m_foundUnhandled = true;
++m_ctx.m_nonRepVarRef;
return;
}
nodep->user1p(getNet(nodep->varp()));
}
void visit(AstConst* nodep) override {
UASSERT_OBJ(!nodep->user1p(), nodep, "Already has Dfg vertex");
if (unhandled(nodep)) return;
Make DfgConst hold V3Number directly Remove intermediary AstConst. No functional change intended.
2022-10-07 16:44:14 +02:00
DfgVertex* const vtxp = new DfgConst{*m_dfgp, nodep->fileline(), nodep->num()};
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
m_uncommittedVertices.push_back(vtxp);
nodep->user1p(vtxp);
}
DFG: Special case representation of AstSel AstSel is a ternary node, but the 'widthp' is always constant and is hence redundant, and 'lsbp' is very often constant. As AstSel is fairly common, we special case as a DfgSel for the constant 'lsbp', and as 'DfgMux` for the non-constant 'lsbp'.
2022-10-06 19:34:18 +02:00
void visit(AstSel* nodep) override {
UASSERT_OBJ(!nodep->user1p(), nodep, "Already has Dfg vertex");
if (unhandled(nodep)) return;
if (!VN_IS(nodep->widthp(), Const)) { // This should never be taken, but paranoia
m_foundUnhandled = true;
++m_ctx.m_nonRepNode;
return;
}
iterate(nodep->fromp());
if (m_foundUnhandled) return;
FileLine* const flp = nodep->fileline();
DfgVertex* vtxp = nullptr;
if (AstConst* const constp = VN_CAST(nodep->lsbp(), Const)) {
DfgSel* const selp = new DfgSel{*m_dfgp, flp, DfgVertex::dtypeFor(nodep)};
selp->fromp(nodep->fromp()->user1u().to<DfgVertex*>());
selp->lsb(constp->toUInt());
vtxp = selp;
} else {
iterate(nodep->lsbp());
if (m_foundUnhandled) return;
DfgMux* const muxp = new DfgMux{*m_dfgp, flp, DfgVertex::dtypeFor(nodep)};
muxp->fromp(nodep->fromp()->user1u().to<DfgVertex*>());
muxp->lsbp(nodep->lsbp()->user1u().to<DfgVertex*>());
vtxp = muxp;
}
m_uncommittedVertices.push_back(vtxp);
nodep->user1p(vtxp);
}
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
// The rest of the 'visit' methods are generated by 'astgen'
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
#include "V3Dfg__gen_ast_to_dfg.h"
// CONSTRUCTOR
explicit AstToDfgVisitor(AstModule& module, V3DfgOptimizationContext& ctx)
: m_dfgp{new DfgGraph{module, module.name()}}
, m_ctx{ctx} {
// Build the DFG
iterateChildren(&module);
UASSERT_OBJ(m_uncommittedVertices.empty(), &module, "Uncommitted vertices remain");
DFG: Support AstSel and AstConcat on LHS of assignments Added DfgVertexVariadic to represent DFG vetices with a varying number of source operands. Converted DfgVar to be a variadic vertex, with each driver corresponding to a fixed range of bits in the packed variable. This allows us to handle AstSel on the LHS of assignments. Also added support for AstConcat on the LHS by selecting into the RHS as appropriate. This improves OpenTitan ST speed by ~13%
2022-09-25 17:03:15 +02:00
DFG: Partial support for unpacked arrays Representation and Ast / Dfg conversions available, for element-wise access only. Not much optimization yet (only CSE).
2022-09-27 01:06:50 +02:00
// Canonicalize variables
canonicalizePacked();
DFG: Remove unconneced variables early
2022-09-30 12:35:03 +02:00
canonicalizeArray();
Introduce DFG based combinational logic optimizer (#3527) Added a new data-flow graph (DFG) based combinational logic optimizer. The capabilities of this covers a combination of V3Const and V3Gate, but is also more capable of transforming combinational logic into simplified forms and more. This entail adding a new internal representation, `DfgGraph`, and appropriate `astToDfg` and `dfgToAst` conversion functions. The graph represents some of the combinational equations (~continuous assignments) in a module, and for the duration of the DFG passes, it takes over the role of AstModule. A bulk of the Dfg vertices represent expressions. These vertex classes, and the corresponding conversions to/from AST are mostly auto-generated by astgen, together with a DfgVVisitor that can be used for dynamic dispatch based on vertex (operation) types. The resulting combinational logic graph (a `DfgGraph`) is then optimized in various ways. Currently we perform common sub-expression elimination, variable inlining, and some specific peephole optimizations, but there is scope for more optimizations in the future using the same representation. The optimizer is run directly before and after inlining. The pre inline pass can operate on smaller graphs and hence converges faster, but still has a chance of substantially reducing the size of the logic on some designs, making inlining both faster and less memory intensive. The post inline pass can then optimize across the inlined module boundaries. No optimization is performed across a module boundary. For debugging purposes, each peephole optimization can be disabled individually via the -fno-dfg-peepnole-<OPT> option, where <OPT> is one of the optimizations listed in V3DfgPeephole.h, for example -fno-dfg-peephole-remove-not-not. The peephole patterns currently implemented were mostly picked based on the design that inspired this work, and on that design the optimizations yields ~30% single threaded speedup, and ~50% speedup on 4 threads. As you can imagine not having to haul around redundant combinational networks in the rest of the compilation pipeline also helps with memory consumption, and up to 30% peak memory usage of Verilator was observed on the same design. Gains on other arbitrary designs are smaller (and can be improved by analyzing those designs). For example OpenTitan gains between 1-15% speedup depending on build type.
2022-09-23 17:46:22 +02:00
}
public:
static DfgGraph* apply(AstModule& module, V3DfgOptimizationContext& ctx) {
return AstToDfgVisitor{module, ctx}.m_dfgp;
}
};
DfgGraph* V3DfgPasses::astToDfg(AstModule& module, V3DfgOptimizationContext& ctx) {
return AstToDfgVisitor::apply(module, ctx);
}