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Optimize Ast read references in Dfg directly (#7354)

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Introduce a new DfgAstRd vertex, which holds an AstNodeExpr that is a
reference to a variable. This enables tracking all read references in
Dfg, which both enables more optimization, and allows inlining of
expressions in place of the reference more intelligently (e.g, when the
expression is only used once, and is not in a loop). This can get rid of
20-30% of temporary variables introduced in Dfg in some designs. Note
V3Gate later got rid of a lot of those, this is a step towards making
V3Gate redundant. The more intelligent expression inlining is worth ~10%
runtime speed on some designs.
This commit is contained in:
Geza Lore
2026-04-01 10:52:56 +01:00
committed by GitHub
parent dbd4823323
commit b4a0ca8ba6
23 changed files with 610 additions and 224 deletions
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src/V3Dfg.cpp
+89 -23
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@@ -80,6 +80,22 @@ std::unique_ptr<DfgGraph> DfgGraph::clone() const {
if (AstNode* const tmpForp = vp->tmpForp()) cp->tmpForp(tmpForp);
}
// Clone ast reference vertices
for (const DfgVertexAst& vtx : m_astVertices) { // LCOV_EXCL_START
switch (vtx.type()) {
case VDfgType::AstRd: {
const DfgAstRd* const vp = vtx.as<DfgAstRd>();
DfgAstRd* const cp = new DfgAstRd{*clonep, vp->exprp(), vp->inSenItem(), vp->inLoop()};
vtxp2clonep.emplace(&vtx, cp);
break;
}
default: {
vtx.v3fatalSrc("Unhandled ast reference vertex type: " + vtx.typeName());
VL_UNREACHABLE;
break;
}
}
} // LCOV_EXCL_STOP
// Clone operation vertices
for (const DfgVertex& vtx : m_opVertices) {
switch (vtx.type()) {
@@ -136,6 +152,22 @@ std::unique_ptr<DfgGraph> DfgGraph::clone() const {
if (const DfgVertex* const srcp = vtx.srcp()) cp->srcp(vtxp2clonep.at(srcp));
if (const DfgVertex* const defp = vtx.defaultp()) cp->defaultp(vtxp2clonep.at(defp));
}
// Hook up inputs of cloned ast references
for (const DfgVertexAst& vtx : m_astVertices) { // LCOV_EXCL_START
switch (vtx.type()) {
case VDfgType::AstRd: {
const DfgAstRd* const vp = vtx.as<DfgAstRd>();
DfgAstRd* const cp = vtxp2clonep.at(&vtx)->as<DfgAstRd>();
if (const DfgVertex* const srcp = vp->srcp()) cp->srcp(vtxp2clonep.at(srcp));
break;
}
default: {
vtx.v3fatalSrc("Unhandled DfgVertexAst sub type: " + vtx.typeName());
VL_UNREACHABLE;
break;
}
}
} // LCOV_EXCL_STOP
// Hook up inputs of cloned operation vertices
for (const DfgVertex& vtx : m_opVertices) {
if (vtx.is<DfgVertexVariadic>()) {
@@ -201,6 +233,14 @@ void DfgGraph::mergeGraphs(std::vector<std::unique_ptr<DfgGraph>>&& otherps) {
#endif
}
m_varVertices.splice(m_varVertices.end(), otherp->m_varVertices);
// Process Ast references
for (DfgVertexAst* const vtxp : otherp->m_astVertices.unlinkable()) {
vtxp->m_userGeneration = 0;
#ifdef VL_DEBUG
vtxp->m_dfgp = this;
#endif
}
m_astVertices.splice(m_astVertices.end(), otherp->m_astVertices);
// Process constants
for (DfgConst& vtx : otherp->m_constVertices) {
vtx.m_userGeneration = 0;
@@ -270,7 +310,6 @@ static const std::string toDotId(const DfgVertex& vtx) { return '"' + cvtToHex(&
static void dumpDotVertex(std::ostream& os, const DfgVertex& vtx) {
if (const DfgVertexVar* const varVtxp = vtx.cast<DfgVertexVar>()) {
const AstNode* const nodep = varVtxp->nodep();
const AstVar* const varp = varVtxp->varp();
os << toDotId(vtx);
// Begin attributes
os << " [";
@@ -292,7 +331,7 @@ static void dumpDotVertex(std::ostream& os, const DfgVertex& vtx) {
os << " / ";
static const char* const rwmn[2][2] = {{"_", "W"}, {"R", "M"}};
os << rwmn[varVtxp->hasExtRdRefs()][varVtxp->hasExtWrRefs()];
os << rwmn[varVtxp->hasModRdRefs()][varVtxp->hasModWrRefs()];
os << rwmn[false][varVtxp->hasModWrRefs()];
os << (varVtxp->hasDfgRefs() ? "D" : "_");
// End 'label'
os << '"';
@@ -305,21 +344,13 @@ static void dumpDotVertex(std::ostream& os, const DfgVertex& vtx) {
varVtxp->v3fatalSrc("Unhandled DfgVertexVar sub-type");
}
// Color
if (varp->direction() == VDirection::INPUT) {
os << ", style=filled, fillcolor=chartreuse2"; // Green
} else if (varp->direction() == VDirection::OUTPUT) {
os << ", style=filled, fillcolor=cyan2"; // Cyan
} else if (varp->direction() == VDirection::INOUT) {
os << ", style=filled, fillcolor=darkorchid2"; // Purple
} else if (varVtxp->hasExtRefs()) {
os << ", style=filled, fillcolor=firebrick2"; // Red
} else if (varVtxp->hasModRefs()) {
os << ", style=filled, fillcolor=darkorange1"; // Orange
} else if (varVtxp->hasDfgRefs()) {
os << ", style=filled, fillcolor=gold2"; // Yellow
} else if (varVtxp->tmpForp()) {
os << ", style=filled, fillcolor=gray95";
}
const char* const colorp = varVtxp->hasExtRefs() ? "firebrick2" // Red
: varVtxp->hasModWrRefs() ? "darkorange1" // Orange
: varVtxp->hasDfgRefs() ? "gold2" // Yellow
: varVtxp->tmpForp() ? "gray95" // Gray
: "white";
os << ", style=filled";
os << ", fillcolor=\"" << colorp << "\"";
// End attributes
os << "]\n";
return;
@@ -379,7 +410,7 @@ static void dumpDotVertex(std::ostream& os, const DfgVertex& vtx) {
os << toDotId(vtx);
std::stringstream ss;
V3EmitV::debugVerilogForTree(logicp->nodep(), ss);
std::string str = ss.str();
std::string str = "AstNode: " + cvtToHex(logicp->nodep()) + "\n" + ss.str();
str = VString::quoteBackslash(str);
str = VString::quoteAny(str, '"', '\\');
str = VString::replaceSubstr(str, "\n", "\\l");
@@ -390,7 +421,32 @@ static void dumpDotVertex(std::ostream& os, const DfgVertex& vtx) {
os << " [label=\"";
os << str;
os << "\\n" << cvtToHex(&vtx);
os << '\n' << vtx.typeName() << '\n' << cvtToHex(&vtx);
os << "\"\n";
os << ", shape=box, style=\"rounded,filled\", nojustify=true";
os << ", fillcolor=\"" << colorp << "\"";
os << "]\n";
return;
}
if (const DfgVertexAst* const astVtxp = vtx.cast<DfgVertexAst>()) {
os << toDotId(vtx);
std::stringstream ss;
V3EmitV::debugVerilogForTree(astVtxp->exprp(), ss);
std::string str = "AstNode: " + cvtToHex(astVtxp->exprp()) + "\n" + ss.str() + "\n";
str = VString::quoteBackslash(str);
str = VString::quoteAny(str, '"', '\\');
str = VString::replaceSubstr(str, "\n", "\\l");
const DfgAstRd* const astRdVtxp = astVtxp->cast<DfgAstRd>();
const char* const colorp = astRdVtxp ? "#80ff80" // Green
: "#ffff80"; // Yellow
os << " [label=\"";
os << str;
os << '\n' << vtx.typeName() << '\n' << cvtToHex(&vtx) << '\n';
vtx.dtype().astDtypep()->dumpSmall(os);
os << " / ";
os << "_S"[astRdVtxp->inSenItem()];
os << "_L"[astRdVtxp->inLoop()];
os << "\"\n";
os << ", shape=box, style=\"rounded,filled\", nojustify=true";
os << ", fillcolor=\"" << colorp << "\"";
@@ -550,6 +606,11 @@ void DfgVertex::typeCheck(const DfgGraph& dfg) const {
CHECK(isPacked(), "Should be Packed type");
return;
}
case VDfgType::AstRd: {
const DfgAstRd& v = *as<DfgAstRd>();
CHECK(v.isPacked() || v.isArray(), "Should be Packed or Array type");
return;
}
case VDfgType::VarArray:
case VDfgType::VarPacked: {
const DfgVertexVar& v = *as<DfgVertexVar>();
@@ -781,16 +842,21 @@ DfgVertexVar* DfgVertex::getResultVar() {
if (!resp->hasDfgRefs()) resp = varp;
return false;
}
// Prefer those that already have module references
if (resp->hasModRdRefs() != varp->hasModRdRefs()) {
if (!resp->hasModRdRefs()) resp = varp;
// Prefer real variables over temporaries
const bool resIsTemp
= resp->varp() ? resp->varp()->isTemp() : resp->varScopep()->varp()->isTemp();
const bool varIsTemp
= varp->varp() ? varp->varp()->isTemp() : varp->varScopep()->varp()->isTemp();
if (resIsTemp != varIsTemp) {
if (resIsTemp) resp = varp;
return false;
}
// Prefer real variabels over temporaries
if (!resp->tmpForp() != !varp->tmpForp()) {
if (resp->tmpForp()) resp = varp;
return false;
}
// Prefer the earlier one in source order
const FileLine& oldFlp = *(resp->fileline());
const FileLine& newFlp = *(varp->fileline());