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verilator/src/V3DfgDfgToAst.cpp

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// -*- mode: C++; c-file-style: "cc-mode" -*-
//*************************************************************************
// DESCRIPTION: Verilator: Convert DfgGraph to AstModule
//
// Code available from: https://verilator.org
//
//*************************************************************************
//
// Copyright 2003-2025 by Wilson Snyder. This program is free software; you
// 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
//
//*************************************************************************
//
// Convert DfgGraph back to AstModule. We recursively construct AstNodeExpr expressions for each
// DfgVertex which represents a storage location (e.g.: DfgVarPacked), or has multiple sinks
// without driving a storage location (and hence needs a temporary variable to duplication). The
// recursion stops when we reach a DfgVertex representing a storage location (e.g.: DfgVarPacked),
// or a vertex that that has multiple sinks (as these nodes will have a [potentially new temporary]
// corresponding// storage location). Redundant variables (those whose source vertex drives
// multiple variables) are eliminated when possible. Vertices driving multiple variables are
// rendered once, driving an arbitrarily (but deterministically) chosen canonical variable, and the
// corresponding redundant variables are assigned from the canonical variable.
//
//*************************************************************************
#include "V3PchAstNoMT.h" // VL_MT_DISABLED_CODE_UNIT
#include "V3Dfg.h"
#include "V3DfgPasses.h"
#include "V3UniqueNames.h"
#include <unordered_map>
VL_DEFINE_DEBUG_FUNCTIONS;
namespace {
// Create an AstNodeExpr out of a DfgVertex. For most AstNodeExpr subtypes, this can be done
// automatically. For the few special cases, we provide specializations below
template <typename T_Node, typename T_Vertex, typename... Ops>
T_Node* makeNode(const T_Vertex* vtxp, Ops... ops) {
T_Node* const nodep = new T_Node{vtxp->fileline(), ops...};
UASSERT_OBJ(nodep->width() == static_cast<int>(vtxp->width()), vtxp,
"Incorrect width in AstNode created from DfgVertex "
<< vtxp->typeName() << ": " << nodep->width() << " vs " << vtxp->width());
return nodep;
}
//======================================================================
// Vertices needing special conversion
template <>
AstExtend* makeNode<AstExtend, DfgExtend, AstNodeExpr*>( //
const DfgExtend* vtxp, AstNodeExpr* op1) {
return new AstExtend{vtxp->fileline(), op1, static_cast<int>(vtxp->width())};
}
template <>
AstExtendS* makeNode<AstExtendS, DfgExtendS, AstNodeExpr*>( //
const DfgExtendS* vtxp, AstNodeExpr* op1) {
return new AstExtendS{vtxp->fileline(), op1, static_cast<int>(vtxp->width())};
}
template <>
AstShiftL* makeNode<AstShiftL, DfgShiftL, AstNodeExpr*, AstNodeExpr*>( //
const DfgShiftL* vtxp, AstNodeExpr* op1, AstNodeExpr* op2) {
return new AstShiftL{vtxp->fileline(), op1, op2, static_cast<int>(vtxp->width())};
}
template <>
AstShiftR* makeNode<AstShiftR, DfgShiftR, AstNodeExpr*, AstNodeExpr*>( //
const DfgShiftR* vtxp, AstNodeExpr* op1, AstNodeExpr* op2) {
return new AstShiftR{vtxp->fileline(), op1, op2, static_cast<int>(vtxp->width())};
}
template <>
AstShiftRS* makeNode<AstShiftRS, DfgShiftRS, AstNodeExpr*, AstNodeExpr*>( //
const DfgShiftRS* vtxp, AstNodeExpr* op1, AstNodeExpr* op2) {
return new AstShiftRS{vtxp->fileline(), op1, op2, static_cast<int>(vtxp->width())};
}
} // namespace
template <bool T_Scoped>
class DfgToAstVisitor final : DfgVisitor {
// NODE STATE
// AstScope::user2p // The combinational AstActive under this scope
const VNUser2InUse m_user2InUse;
// TYPES
using Variable = std::conditional_t<T_Scoped, AstVarScope, AstVar>;
using Container = std::conditional_t<T_Scoped, AstActive, AstNodeModule>;
// STATE
AstModule* const m_modp; // The parent/result module - This is nullptr when T_Scoped
V3DfgDfgToAstContext& m_ctx; // The context for stats
AstNodeExpr* m_resultp = nullptr; // The result node of the current traversal
AstAlways* m_alwaysp = nullptr; // Process to add assignments to, if have a default driver
Container* m_containerp = nullptr; // The AstNodeModule or AstActive to insert assigns into
// METHODS
static Variable* getNode(const DfgVertexVar* vtxp) {
if VL_CONSTEXPR_CXX17 (T_Scoped) {
return reinterpret_cast<Variable*>(vtxp->varScopep());
} else {
return reinterpret_cast<Variable*>(vtxp->varp());
}
}
static AstActive* getCombActive(AstScope* scopep) {
if (!scopep->user2p()) {
// Try to find the existing combinational AstActive
for (AstNode* nodep = scopep->blocksp(); nodep; nodep = nodep->nextp()) {
AstActive* const activep = VN_CAST(nodep, Active);
if (!activep) continue;
if (activep->hasCombo()) {
scopep->user2p(activep);
break;
}
}
// If there isn't one, create a new one
if (!scopep->user2p()) {
FileLine* const flp = scopep->fileline();
AstSenTree* const senTreep
= new AstSenTree{flp, new AstSenItem{flp, AstSenItem::Combo{}}};
AstActive* const activep = new AstActive{flp, "", senTreep};
activep->senTreeStorep(senTreep);
scopep->addBlocksp(activep);
scopep->user2p(activep);
}
}
return VN_AS(scopep->user2p(), Active);
}
AstNodeExpr* convertDfgVertexToAstNodeExpr(DfgVertex* vtxp) {
UASSERT_OBJ(!m_resultp, vtxp, "Result already computed");
UASSERT_OBJ(vtxp->is<DfgVertexVar>() || vtxp->is<DfgConst>() //
|| !vtxp->hasMultipleSinks() || vtxp->isCheaperThanLoad(), //
vtxp, "Intermediate DFG value with multiple uses");
iterate(vtxp);
UASSERT_OBJ(m_resultp, vtxp, "Missing result");
AstNodeExpr* const resultp = m_resultp;
m_resultp = nullptr;
return resultp;
}
void createAssignment(FileLine* flp, AstNodeExpr* lhsp, DfgVertex* driverp) {
// Keep track of statisticss
++m_ctx.m_resultEquations;
// Render the driver
AstNodeExpr* const rhsp = convertDfgVertexToAstNodeExpr(driverp);
// Update LHS locations to reflect the location of the original driver
lhsp->foreach([&](AstNode* nodep) { nodep->fileline(flp); });
// If using a process, add Assign there
if (m_alwaysp) {
m_alwaysp->addStmtsp(new AstAssign{flp, lhsp, rhsp});
return;
}
// Otherwise create an AssignW
AstAssignW* const ap = new AstAssignW{flp, lhsp, rhsp};
m_containerp->addStmtsp(new AstAlways{ap});
}
void convertDriver(FileLine* flp, AstNodeExpr* lhsp, DfgVertex* driverp) {
if (DfgSplicePacked* const sPackedp = driverp->cast<DfgSplicePacked>()) {
// Partial assignment of packed value
sPackedp->foreachDriver([&](DfgVertex& src, uint32_t lo, FileLine* dflp) {
// Create Sel
AstConst* const lsbp = new AstConst{dflp, lo};
const int width = static_cast<int>(src.width());
AstSel* const nLhsp = new AstSel{dflp, lhsp->cloneTreePure(false), lsbp, width};
// Convert source
convertDriver(dflp, nLhsp, &src);
// Delete Sel - was cloned
VL_DO_DANGLING(nLhsp->deleteTree(), nLhsp);
return false;
});
return;
}
if (DfgSpliceArray* const sArrayp = driverp->cast<DfgSpliceArray>()) {
// Partial assignment of array variable
sArrayp->foreachDriver([&](DfgVertex& src, uint32_t lo, FileLine* dflp) {
UASSERT_OBJ(src.size() == 1, &src, "We only handle single elements");
// Create ArraySel
AstConst* const idxp = new AstConst{dflp, lo};
AstArraySel* const nLhsp = new AstArraySel{dflp, lhsp->cloneTreePure(false), idxp};
// Convert source
if (const DfgUnitArray* const uap = src.cast<DfgUnitArray>()) {
convertDriver(dflp, nLhsp, uap->srcp());
} else {
convertDriver(dflp, nLhsp, &src);
}
// Delete ArraySel - was cloned
VL_DO_DANGLING(nLhsp->deleteTree(), nLhsp);
return false;
});
return;
}
if (const DfgUnitArray* const uap = driverp->cast<DfgUnitArray>()) {
// Single element array being assigned a unit array. Needs an ArraySel.
AstConst* const idxp = new AstConst{flp, 0};
AstArraySel* const nLhsp = new AstArraySel{flp, lhsp->cloneTreePure(false), idxp};
// Convert source
convertDriver(flp, nLhsp, uap->srcp());
// Delete ArraySel - was cloned
VL_DO_DANGLING(nLhsp->deleteTree(), nLhsp);
return;
}
// Base case: assign vertex to current lhs
createAssignment(flp, lhsp->cloneTreePure(false), driverp);
}
// VISITORS
void visit(DfgVertex* vtxp) override { // LCOV_EXCL_START
vtxp->v3fatalSrc("Unhandled DfgVertex: " << vtxp->typeName());
} // LCOV_EXCL_STOP
void visit(DfgVarPacked* vtxp) override {
m_resultp = new AstVarRef{vtxp->fileline(), getNode(vtxp), VAccess::READ};
}
void visit(DfgVarArray* vtxp) override {
m_resultp = new AstVarRef{vtxp->fileline(), getNode(vtxp), VAccess::READ};
}
void visit(DfgConst* vtxp) override { //
m_resultp = new AstConst{vtxp->fileline(), vtxp->num()};
}
void visit(DfgSel* vtxp) override {
FileLine* const flp = vtxp->fileline();
AstNodeExpr* const fromp = convertDfgVertexToAstNodeExpr(vtxp->fromp());
AstConst* const lsbp = new AstConst{flp, vtxp->lsb()};
m_resultp = new AstSel{flp, fromp, lsbp, static_cast<int>(vtxp->width())};
}
void visit(DfgMux* vtxp) override {
FileLine* const flp = vtxp->fileline();
AstNodeExpr* const fromp = convertDfgVertexToAstNodeExpr(vtxp->fromp());
AstNodeExpr* const lsbp = convertDfgVertexToAstNodeExpr(vtxp->lsbp());
m_resultp = new AstSel{flp, fromp, lsbp, static_cast<int>(vtxp->width())};
}
// The rest of the 'visit' methods are generated by 'astgen'
#include "V3Dfg__gen_dfg_to_ast.h"
// Constructor
DfgToAstVisitor(DfgGraph& dfg, V3DfgDfgToAstContext& ctx)
: m_modp{dfg.modulep()}
, m_ctx{ctx} {
if (v3Global.opt.debugCheck()) V3DfgPasses::typeCheck(dfg);
// Convert the graph back to combinational assignments
// The graph must have been regularized, so we only need to render assignments
for (DfgVertexVar& vtx : dfg.varVertices()) {
// If there is no driver (this vertex is an input to the graph), then nothing to do.
if (!vtx.srcp()) {
UASSERT_OBJ(!vtx.defaultp(), &vtx, "Only default driver on variable");
continue;
}
++m_ctx.m_outputVariables;
// Render variable assignments
FileLine* const flp = vtx.driverFileLine() ? vtx.driverFileLine() : vtx.fileline();
AstVarRef* const lhsp = new AstVarRef{flp, getNode(&vtx), VAccess::WRITE};
VL_RESTORER(m_containerp);
if VL_CONSTEXPR_CXX17 (T_Scoped) {
// Add it to the scope holding the target variable
AstActive* const activep = getCombActive(vtx.varScopep()->scopep());
m_containerp = reinterpret_cast<Container*>(activep);
} else {
// Add it to the parent module of the DfgGraph
m_containerp = reinterpret_cast<Container*>(m_modp);
}
// If there is a default value, render all drivers under an AstAlways
VL_RESTORER(m_alwaysp);
if (DfgVertex* const defaultp = vtx.defaultp()) {
++m_ctx.m_outputVariablesWithDefault;
m_alwaysp = new AstAlways{vtx.fileline(), VAlwaysKwd::ALWAYS_COMB, nullptr};
m_containerp->addStmtsp(m_alwaysp);
// The default assignment needs to go first
createAssignment(vtx.fileline(), lhsp->cloneTreePure(false), defaultp);
}
// Render the drivers
convertDriver(flp, lhsp, vtx.srcp());
// convetDriver always clones lhsp
VL_DO_DANGLING(lhsp->deleteTree(), lhsp);
}
}
public:
static void apply(DfgGraph& dfg, V3DfgDfgToAstContext& ctx) { DfgToAstVisitor{dfg, ctx}; }
};
void V3DfgPasses::dfgToAst(DfgGraph& dfg, V3DfgContext& ctx) {
if (dfg.modulep()) {
DfgToAstVisitor</* T_Scoped: */ false>::apply(dfg, ctx.m_dfg2AstContext);
} else {
DfgToAstVisitor</* T_Scoped: */ true>::apply(dfg, ctx.m_dfg2AstContext);
}
}
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