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Optimize redundant memoization in DFG CSE (#8285)

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This commit is contained in:
Geza Lore
2026-09-05 12:13:11 -04:00
committed by GitHub
parent b907a1a75d
commit bcf613c4fe
1 changed files with 19 additions and 13 deletions
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src/V3DfgCse.cpp
+19 -13
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@@ -262,6 +262,18 @@ class V3DfgCse final {
VL_UNREACHABLE;
}
// Compares the sources of 'a' and 'b' for equivalence
bool sourcesEquivalent(const DfgVertex& a, const DfgVertex& b) {
for (size_t i = 0; i < a.nInputs(); ++i) {
const DfgVertex* const ap = a.inputp(i);
const DfgVertex* const bp = b.inputp(i);
if (!ap && !bp) continue;
if (!ap || !bp) return false;
if (!vertexEquivalent(*ap, *bp)) return false;
}
return true;
}
// Compares 'a' and 'b' for equivalence
bool vertexEquivalent(const DfgVertex& a, const DfgVertex& b) {
// If same vertex, then equal
@@ -279,23 +291,17 @@ class V3DfgCse final {
// Check vertex specifics
if (!vertexSelfEquivalent(a, b)) return false;
// A given pair can only be reached more than once if one of the
// vertices has multiple sinks, or if there was a hash collision.
// Collisions are rare, so only memoize the result if it can actually
// be looked up again through multiple paths.
if (!a.hasMultipleSinks() && !b.hasMultipleSinks()) return sourcesEquivalent(a, b);
// Check sources
const VertexPair key = (&a < &b) ? std::make_pair(&a, &b) : std::make_pair(&b, &a);
// The recursive invocation can cause a re-hash but that will not invalidate references
uint8_t& result = m_equivalentCache[key];
if (!result) {
const bool equal = [&]() {
for (size_t i = 0; i < a.nInputs(); ++i) {
const DfgVertex* const ap = a.inputp(i);
const DfgVertex* const bp = b.inputp(i);
if (!ap && !bp) continue;
if (!ap || !bp) return false;
if (!vertexEquivalent(*ap, *bp)) return false;
}
return true;
}();
result = (static_cast<uint8_t>(equal) << 1) | 1;
}
if (!result) result = (static_cast<uint8_t>(sourcesEquivalent(a, b)) << 1) | 1;
return result >> 1;
}