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Internals: Move Dfg CSE into separate source file (#6363)

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Parts of this algorithm were distributed over many files some
masquerading as re-usable APIs, they were not. Move everything into one
file and avoid unnecessary virtual functions.
This commit is contained in:
Geza Lore
2025-09-03 17:34:55 +01:00
committed by GitHub
parent 5161cea8cd
commit a49334f3e4
8 changed files with 338 additions and 202 deletions
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src/V3DfgPasses.cpp
-55
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@@ -25,61 +25,6 @@
VL_DEFINE_DEBUG_FUNCTIONS;
// Common sub-expression elimination
void V3DfgPasses::cse(DfgGraph& dfg, V3DfgCseContext& ctx) {
// Remove common sub-expressions
{
// Used by DfgVertex::hash
DfgUserMap<V3Hash> hashCache = dfg.makeUserMap<V3Hash>();
DfgVertex::EqualsCache equalsCache;
std::unordered_map<V3Hash, std::vector<DfgVertex*>> verticesWithEqualHashes;
verticesWithEqualHashes.reserve(dfg.size());
// Pre-hash variables, these are all unique, so just set their hash to a unique value
uint32_t varHash = 0;
for (const DfgVertexVar& vtx : dfg.varVertices()) hashCache[vtx] = V3Hash{++varHash};
// Similarly pre-hash constants for speed. While we don't combine constants, we do want
// expressions using the same constants to be combined, so we do need to hash equal
// constants to equal values.
for (DfgConst* const vtxp : dfg.constVertices().unlinkable()) {
// Delete unused constants while we are at it.
if (!vtxp->hasSinks()) {
VL_DO_DANGLING(vtxp->unlinkDelete(dfg), vtxp);
continue;
}
hashCache[vtxp] = vtxp->num().toHash() + varHash;
}
// Combine operation vertices
for (DfgVertex* const vtxp : dfg.opVertices().unlinkable()) {
// Delete unused nodes while we are at it.
if (!vtxp->hasSinks()) {
vtxp->unlinkDelete(dfg);
continue;
}
const V3Hash hash = vtxp->hash(hashCache);
std::vector<DfgVertex*>& vec = verticesWithEqualHashes[hash];
bool replaced = false;
for (DfgVertex* const candidatep : vec) {
if (candidatep->equals(*vtxp, equalsCache)) {
++ctx.m_eliminated;
vtxp->replaceWith(candidatep);
VL_DO_DANGLING(vtxp->unlinkDelete(dfg), vtxp);
replaced = true;
break;
}
}
if (replaced) continue;
vec.push_back(vtxp);
}
}
// Prune unused nodes
removeUnused(dfg);
}
void V3DfgPasses::inlineVars(DfgGraph& dfg) {
for (DfgVertexVar& vtx : dfg.varVertices()) {
if (DfgVarPacked* const varp = vtx.cast<DfgVarPacked>()) {