420 lines
16 KiB
C++
420 lines
16 KiB
C++
// -*- mode: C++; c-file-style: "cc-mode" -*-
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//*************************************************************************
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// DESCRIPTION: Verilator: Convert AstModule to DfgGraph
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//
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// Code available from: https://verilator.org
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//
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//*************************************************************************
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//
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// Copyright 2003-2022 by Wilson Snyder. This program is free software; you
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// can redistribute it and/or modify it under the terms of either the GNU
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// Lesser General Public License Version 3 or the Perl Artistic License
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// Version 2.0.
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// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
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//
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//*************************************************************************
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//
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// Convert and AstModule to a DfgGraph. We proceed by visiting convertable logic blocks (e.g.:
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// AstAssignW of appropriate type and with no delays), recursively constructing DfgVertex instances
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// for the expressions that compose the subject logic block. If all expressions in the current
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// logic block can be converted, then we delete the logic block (now represented in the DfgGraph),
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// and connect the corresponding DfgVertex instances appropriately. If some of the expressions were
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// not convertible in the current logic block, we revert (delete) the DfgVertex instances created
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// for the logic block, and leave the logic block in the AstModule. Any variable reference from
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// non-converted logic blocks (or other constructs under the AstModule) are marked as being
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// referenced in the AstModule, which is relevant for later optimization.
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//
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//*************************************************************************
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#include "config_build.h"
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#include "verilatedos.h"
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#include "V3Ast.h"
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#include "V3Dfg.h"
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#include "V3DfgPasses.h"
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#include "V3Error.h"
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#include "V3Global.h"
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VL_DEFINE_DEBUG_FUNCTIONS;
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namespace {
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// Create a DfgVertex out of a AstNodeMath. For most AstNodeMath subtypes, this can be done
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// automatically. For the few special cases, we provide specializations below
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template <typename Vertex>
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Vertex* makeVertex(const AstForDfg<Vertex>* nodep, DfgGraph& dfg) {
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return new Vertex{dfg, nodep->fileline(), DfgVertex::dtypeFor(nodep)};
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}
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//======================================================================
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// Currently unhandled nodes
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// LCOV_EXCL_START
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// AstCCast changes width, but should not exists where DFG optimization is currently invoked
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template <>
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DfgCCast* makeVertex<DfgCCast>(const AstCCast*, DfgGraph&) {
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return nullptr;
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}
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// Unhandled in DfgToAst, but also operates on strings which we don't optimize anyway
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template <>
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DfgAtoN* makeVertex<DfgAtoN>(const AstAtoN*, DfgGraph&) {
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return nullptr;
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}
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// Unhandled in DfgToAst, but also operates on strings which we don't optimize anyway
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template <>
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DfgCompareNN* makeVertex<DfgCompareNN>(const AstCompareNN*, DfgGraph&) {
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return nullptr;
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}
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// Unhandled in DfgToAst, but also operates on unpacked arrays which we don't optimize anyway
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template <>
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DfgSliceSel* makeVertex<DfgSliceSel>(const AstSliceSel*, DfgGraph&) {
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return nullptr;
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}
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// LCOV_EXCL_STOP
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} // namespace
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class AstToDfgVisitor final : public VNVisitor {
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// NODE STATE
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// AstNode::user1p // DfgVertex for this AstNode
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const VNUser1InUse m_user1InUse;
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// STATE
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DfgGraph* const m_dfgp; // The graph being built
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V3DfgOptimizationContext& m_ctx; // The optimization context for stats
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bool m_foundUnhandled = false; // Found node not implemented as DFG or not implemented 'visit'
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std::vector<DfgVertex*> m_uncommittedVertices; // Vertices that we might decide to revert
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bool m_converting = false; // We are trying to convert some logic at the moment
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std::vector<DfgVarPacked*> m_varPackedps; // All the DfgVarPacked vertices we created.
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std::vector<DfgVarArray*> m_varArrayps; // All the DfgVarArray vertices we created.
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// METHODS
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void markReferenced(AstNode* nodep) {
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nodep->foreach<AstVarRef>([this](const AstVarRef* refp) {
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// No need to (and in fact cannot) mark variables with unsupported dtypes
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if (!DfgVertex::isSupportedDType(refp->varp()->dtypep())) return;
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getNet(refp->varp())->setHasModRefs();
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});
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}
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void commitVertices() { m_uncommittedVertices.clear(); }
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void revertUncommittedVertices() {
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for (DfgVertex* const vtxp : m_uncommittedVertices) vtxp->unlinkDelete(*m_dfgp);
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m_uncommittedVertices.clear();
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}
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DfgVertexLValue* getNet(AstVar* varp) {
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if (!varp->user1p()) {
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// Note DfgVertexLValue vertices are not added to m_uncommittedVertices, because we
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// want to hold onto them via AstVar::user1p, and the AstVar might be referenced via
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// multiple AstVarRef instances, so we will never revert a DfgVertexLValue once
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// created. This means we can end up with DfgVertexLValue vertices in the graph which
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// have no connections at all (which is fine for later processing).
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if (VN_IS(varp->dtypep()->skipRefp(), UnpackArrayDType)) {
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DfgVarArray* const vtxp = new DfgVarArray{*m_dfgp, varp};
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varp->user1p();
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m_varArrayps.push_back(vtxp);
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varp->user1p(vtxp);
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} else {
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DfgVarPacked* const vtxp = new DfgVarPacked{*m_dfgp, varp};
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m_varPackedps.push_back(vtxp);
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varp->user1p(vtxp);
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}
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}
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return varp->user1u().to<DfgVertexLValue*>();
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}
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DfgVertex* getVertex(AstNode* nodep) {
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DfgVertex* vtxp = nodep->user1u().to<DfgVertex*>();
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UASSERT_OBJ(vtxp, nodep, "Missing Dfg vertex");
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return vtxp;
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}
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// Returns true if the expression cannot (or should not) be represented by DFG
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bool unhandled(AstNodeMath* nodep) {
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// Short-circuiting if something was already unhandled
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if (!m_foundUnhandled) {
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// Impure nodes cannot be represented
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if (!nodep->isPure()) {
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m_foundUnhandled = true;
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++m_ctx.m_nonRepImpure;
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}
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// Check node has supported dtype
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if (!DfgVertex::isSupportedDType(nodep->dtypep())) {
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m_foundUnhandled = true;
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++m_ctx.m_nonRepDType;
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}
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}
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return m_foundUnhandled;
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}
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// Build DfgEdge representing the LValue assignment. Returns false if unsuccessful.
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bool convertAssignment(FileLine* flp, AstNode* nodep, DfgVertex* vtxp) {
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if (AstVarRef* const vrefp = VN_CAST(nodep, VarRef)) {
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m_foundUnhandled = false;
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visit(vrefp);
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if (m_foundUnhandled) return false;
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getVertex(vrefp)->as<DfgVarPacked>()->addDriver(flp, 0, vtxp);
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return true;
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}
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if (AstSel* const selp = VN_CAST(nodep, Sel)) {
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AstVarRef* const vrefp = VN_CAST(selp->fromp(), VarRef);
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const AstConst* const lsbp = VN_CAST(selp->lsbp(), Const);
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if (!vrefp || !lsbp || !VN_IS(selp->widthp(), Const)) {
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++m_ctx.m_nonRepLhs;
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return false;
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}
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m_foundUnhandled = false;
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visit(vrefp);
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if (m_foundUnhandled) return false;
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getVertex(vrefp)->as<DfgVarPacked>()->addDriver(flp, lsbp->toUInt(), vtxp);
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return true;
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}
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if (AstArraySel* const selp = VN_CAST(nodep, ArraySel)) {
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AstVarRef* const vrefp = VN_CAST(selp->fromp(), VarRef);
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const AstConst* const idxp = VN_CAST(selp->bitp(), Const);
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if (!vrefp || !idxp) {
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++m_ctx.m_nonRepLhs;
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return false;
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}
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m_foundUnhandled = false;
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visit(vrefp);
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if (m_foundUnhandled) return false;
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getVertex(vrefp)->as<DfgVarArray>()->addDriver(flp, idxp->toUInt(), vtxp);
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return true;
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}
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if (AstConcat* const concatp = VN_CAST(nodep, Concat)) {
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AstNode* const lhsp = concatp->lhsp();
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AstNode* const rhsp = concatp->rhsp();
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const uint32_t lWidth = lhsp->width();
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const uint32_t rWidth = rhsp->width();
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{
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FileLine* const lFlp = lhsp->fileline();
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DfgSel* const lVtxp = new DfgSel{*m_dfgp, lFlp, DfgVertex::dtypeFor(lhsp)};
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lVtxp->fromp(vtxp);
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lVtxp->lsbp(new DfgConst{*m_dfgp, new AstConst{lFlp, rWidth}});
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lVtxp->widthp(new DfgConst{*m_dfgp, new AstConst{lFlp, lWidth}});
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if (!convertAssignment(flp, lhsp, lVtxp)) return false;
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}
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{
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FileLine* const rFlp = rhsp->fileline();
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DfgSel* const rVtxp = new DfgSel{*m_dfgp, rFlp, DfgVertex::dtypeFor(rhsp)};
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rVtxp->fromp(vtxp);
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rVtxp->lsbp(new DfgConst{*m_dfgp, new AstConst{rFlp, 0u}});
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rVtxp->widthp(new DfgConst{*m_dfgp, new AstConst{rFlp, rWidth}});
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return convertAssignment(flp, rhsp, rVtxp);
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}
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}
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++m_ctx.m_nonRepLhs;
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return false;
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}
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bool convertEquation(AstNode* nodep, AstNode* lhsp, AstNode* rhsp) {
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UASSERT_OBJ(m_uncommittedVertices.empty(), nodep, "Should not nest");
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// Currently cannot handle direct assignments between unpacked types. These arise e.g.
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// when passing an unpacked array through a module port.
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if (!DfgVertex::isSupportedPackedDType(lhsp->dtypep())
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|| !DfgVertex::isSupportedPackedDType(rhsp->dtypep())) {
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markReferenced(nodep);
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++m_ctx.m_nonRepDType;
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return false;
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}
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// Cannot handle mismatched widths. Mismatched assignments should have been fixed up in
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// earlier passes anyway, so this should never be hit, but being paranoid just in case.
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if (lhsp->width() != rhsp->width()) { // LCOV_EXCL_START
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markReferenced(nodep);
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++m_ctx.m_nonRepWidth;
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return false;
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} // LCOV_EXCL_STOP
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VL_RESTORER(m_converting);
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m_converting = true;
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m_foundUnhandled = false;
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iterate(rhsp);
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if (m_foundUnhandled) {
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revertUncommittedVertices();
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markReferenced(nodep);
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return false;
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}
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if (!convertAssignment(nodep->fileline(), lhsp, getVertex(rhsp))) {
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revertUncommittedVertices();
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markReferenced(nodep);
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return false;
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}
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// Connect the rhs vertex to the driven edge
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commitVertices();
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// Remove node from Ast. Now represented by the Dfg.
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VL_DO_DANGLING(nodep->unlinkFrBack()->deleteTree(), nodep);
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//
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++m_ctx.m_representable;
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return true;
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}
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// Canonicalize packed variables
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void canonicalizePacked() {
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for (DfgVarPacked* const varp : m_varPackedps) {
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// Gather (and unlink) all drivers
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struct Driver {
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FileLine* flp;
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uint32_t lsb;
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DfgVertex* vtxp;
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Driver(FileLine* flp, uint32_t lsb, DfgVertex* vtxp)
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: flp{flp}
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, lsb{lsb}
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, vtxp{vtxp} {}
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};
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std::vector<Driver> drivers;
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drivers.reserve(varp->arity());
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varp->forEachSourceEdge([varp, &drivers](DfgEdge& edge, size_t idx) {
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UASSERT(edge.sourcep(), "Should not have created undriven sources");
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drivers.emplace_back(varp->driverFileLine(idx), varp->driverLsb(idx),
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edge.sourcep());
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edge.unlinkSource();
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});
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// Sort drivers by LSB
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std::stable_sort(drivers.begin(), drivers.end(),
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[](const Driver& a, const Driver& b) { return a.lsb < b.lsb; });
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// TODO: bail on multidriver
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// Coalesce adjacent ranges
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for (size_t i = 0, j = 1; j < drivers.size(); ++j) {
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Driver& a = drivers[i];
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Driver& b = drivers[j];
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// Coalesce adjacent range
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const uint32_t aWidth = a.vtxp->width();
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const uint32_t bWidth = b.vtxp->width();
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if (a.lsb + aWidth == b.lsb) {
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const auto dtypep = DfgVertex::dtypeForWidth(aWidth + bWidth);
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DfgConcat* const concatp = new DfgConcat{*m_dfgp, a.flp, dtypep};
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concatp->rhsp(a.vtxp);
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concatp->lhsp(b.vtxp);
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a.vtxp = concatp;
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b.vtxp = nullptr; // Mark as moved
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++m_ctx.m_coalescedAssignments;
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continue;
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}
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++i;
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// Compact non-adjacent ranges within the vector
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if (j != i) {
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Driver& c = drivers[i];
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UASSERT_OBJ(!c.vtxp, c.flp, "Should have been marked moved");
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c = b;
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b.vtxp = nullptr; // Mark as moved
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}
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}
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// Reinsert sources in order
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varp->resetSources();
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for (const Driver& driver : drivers) {
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if (!driver.vtxp) break; // Stop at end of cmpacted list
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varp->addDriver(driver.flp, driver.lsb, driver.vtxp);
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}
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}
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}
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// VISITORS
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void visit(AstNode* nodep) override {
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// Conservatively treat this node as unhandled
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if (!m_foundUnhandled && m_converting) ++m_ctx.m_nonRepUnknown;
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m_foundUnhandled = true;
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markReferenced(nodep);
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}
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void visit(AstCell* nodep) override { markReferenced(nodep); }
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void visit(AstNodeProcedure* nodep) override { markReferenced(nodep); }
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void visit(AstVar* nodep) override {
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// No need to (and in fact cannot) handle variables with unsupported dtypes
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if (!DfgVertex::isSupportedDType(nodep->dtypep())) return;
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// Mark ports as having external references
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if (nodep->isIO()) getNet(nodep)->setHasExtRefs();
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// Mark variables that are the target of a hierarchical reference
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// (these flags were set up in DataflowPrepVisitor)
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if (nodep->user2()) getNet(nodep)->setHasExtRefs();
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}
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void visit(AstAssignW* nodep) override {
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++m_ctx.m_inputEquations;
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// Cannot handle assignment with timing control yet
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if (nodep->timingControlp()) {
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markReferenced(nodep);
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++m_ctx.m_nonRepTiming;
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return;
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}
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convertEquation(nodep, nodep->lhsp(), nodep->rhsp());
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}
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void visit(AstVarRef* nodep) override {
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UASSERT_OBJ(!nodep->user1p(), nodep, "Already has Dfg vertex");
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if (unhandled(nodep)) return;
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if (nodep->access().isRW() // Cannot represent read-write references
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|| nodep->varp()->isIfaceRef() // Cannot handle interface references
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|| nodep->varp()->delayp() // Cannot handle delayed variables
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|| nodep->classOrPackagep() // Cannot represent cross module references
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) {
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markReferenced(nodep);
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m_foundUnhandled = true;
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++m_ctx.m_nonRepVarRef;
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return;
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}
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// Sadly sometimes AstVarRef does not have the same dtype as the referenced variable
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if (!DfgVertex::isSupportedDType(nodep->varp()->dtypep())) {
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m_foundUnhandled = true;
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++m_ctx.m_nonRepVarRef;
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return;
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}
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nodep->user1p(getNet(nodep->varp()));
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}
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void visit(AstConst* nodep) override {
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UASSERT_OBJ(!nodep->user1p(), nodep, "Already has Dfg vertex");
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if (unhandled(nodep)) return;
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DfgVertex* const vtxp = new DfgConst{*m_dfgp, nodep->cloneTree(false)};
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m_uncommittedVertices.push_back(vtxp);
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nodep->user1p(vtxp);
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}
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// The rest of the 'visit' methods are generated by 'astgen'
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#include "V3Dfg__gen_ast_to_dfg.h"
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// CONSTRUCTOR
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explicit AstToDfgVisitor(AstModule& module, V3DfgOptimizationContext& ctx)
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: m_dfgp{new DfgGraph{module, module.name()}}
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, m_ctx{ctx} {
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// Build the DFG
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iterateChildren(&module);
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UASSERT_OBJ(m_uncommittedVertices.empty(), &module, "Uncommitted vertices remain");
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// Canonicalize variables
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canonicalizePacked();
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}
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public:
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static DfgGraph* apply(AstModule& module, V3DfgOptimizationContext& ctx) {
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return AstToDfgVisitor{module, ctx}.m_dfgp;
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}
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};
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DfgGraph* V3DfgPasses::astToDfg(AstModule& module, V3DfgOptimizationContext& ctx) {
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return AstToDfgVisitor::apply(module, ctx);
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}
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