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Optimize $countones constant in Dfg

This commit is contained in:
Geza Lore 2026-06-05 13:00:31 +01:00
parent ca376d681a
commit e35b2429ff
2 changed files with 6 additions and 0 deletions
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5
src/V3DfgPeephole.cpp
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@ -138,6 +138,7 @@ template <> const DfgDataType& resultDType<DfgXor> (const DfgVertex* lhsp
// Unary constant folding
template<typename Vertex> void foldOp(V3Number& out, const V3Number& src);
template <> void foldOp<DfgCountOnes> (V3Number& out, const V3Number& src) { out.opCountOnes(src); }
template <> void foldOp<DfgExtend> (V3Number& out, const V3Number& src) { out.opAssign(src); }
template <> void foldOp<DfgExtendS> (V3Number& out, const V3Number& src) { out.opExtendS(src, src.width()); }
template <> void foldOp<DfgLogNot> (V3Number& out, const V3Number& src) { out.opLogNot(src); }
@ -1195,6 +1196,10 @@ class V3DfgPeephole final : public DfgVisitor {
// DfgVertexUnary
//=========================================================================
void visit(DfgCountOnes* const vtxp) override {
if (foldUnary(vtxp)) return;
}
void visit(DfgExtend* const vtxp) override {
if (foldUnary(vtxp)) return;

1
test_regress/t/t_dfg_peephole.v
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@ -62,6 +62,7 @@ module t (
//verilator lint_on WIDTH
`signal(FOLD_UNARY_Extend, tmp_FOLD_UNARY_Extend);
`signal(FOLD_UNARY_ExtendS, tmp_FOLD_UNARY_ExtendS);
`signal(FOLD_UNARY_CountOnes, $countones(const_a));
`signal(FOLD_UNARY_OneHot, $onehot(const_a));
`signal(FOLD_UNARY_OneHot0, $onehot0(const_a));
`signal(FOLD_UNARY_OneHot_A, $onehot(const_a[0]));