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Optimize $onehot in Dfg

This commit is contained in:
Geza Lore 2026-06-05 12:56:46 +01:00
parent e53d6d9006
commit ca376d681a
5 changed files with 25 additions and 1 deletions
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2
src/V3AstNodeExpr.h
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@ -5784,6 +5784,7 @@ public:
};
class AstOneHot final : public AstNodeUniop {
// True if only single bit set in vector
// @astgen makeDfgVertex
public:
AstOneHot(FileLine* fl, AstNodeExpr* lhsp)
: ASTGEN_SUPER_OneHot(fl, lhsp) {
@ -5801,6 +5802,7 @@ public:
};
class AstOneHot0 final : public AstNodeUniop {
// True if only single bit, or no bits set in vector
// @astgen makeDfgVertex
public:
AstOneHot0(FileLine* fl, AstNodeExpr* lhsp)
: ASTGEN_SUPER_OneHot0(fl, lhsp) {

4
src/V3Dfg.cpp
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@ -774,7 +774,9 @@ void DfgVertex::typeCheck(const DfgGraph& dfg) const {
case VDfgType::LogNot:
case VDfgType::RedAnd:
case VDfgType::RedOr:
case VDfgType::RedXor: {
case VDfgType::RedXor:
case VDfgType::OneHot:
case VDfgType::OneHot0: {
CHECK(dtype() == DfgDataType::packed(1), "Should be 1-bit");
CHECK(inputp(0)->isPacked(), "Operand should be Packed type");
return;

4
src/V3DfgCse.cpp
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@ -110,6 +110,8 @@ class V3DfgCse final {
case VDfgType::NeqCase:
case VDfgType::NeqWild:
case VDfgType::Not:
case VDfgType::OneHot:
case VDfgType::OneHot0:
case VDfgType::Or:
case VDfgType::Pow:
case VDfgType::PowSS:
@ -232,6 +234,8 @@ class V3DfgCse final {
case VDfgType::NeqCase:
case VDfgType::NeqWild:
case VDfgType::Not:
case VDfgType::OneHot:
case VDfgType::OneHot0:
case VDfgType::Or:
case VDfgType::Pow:
case VDfgType::PowSS:

10
src/V3DfgPeephole.cpp
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@ -143,6 +143,8 @@ template <> void foldOp<DfgExtendS> (V3Number& out, const V3Number& src) { ou
template <> void foldOp<DfgLogNot> (V3Number& out, const V3Number& src) { out.opLogNot(src); }
template <> void foldOp<DfgNegate> (V3Number& out, const V3Number& src) { out.opNegate(src); }
template <> void foldOp<DfgNot> (V3Number& out, const V3Number& src) { out.opNot(src); }
template <> void foldOp<DfgOneHot> (V3Number& out, const V3Number& src) { out.opOneHot(src); }
template <> void foldOp<DfgOneHot0> (V3Number& out, const V3Number& src) { out.opOneHot0(src); }
template <> void foldOp<DfgRedAnd> (V3Number& out, const V3Number& src) { out.opRedAnd(src); }
template <> void foldOp<DfgRedOr> (V3Number& out, const V3Number& src) { out.opRedOr(src); }
template <> void foldOp<DfgRedXor> (V3Number& out, const V3Number& src) { out.opRedXor(src); }
@ -1325,6 +1327,14 @@ class V3DfgPeephole final : public DfgVisitor {
}
}
void visit(DfgOneHot* const vtxp) override {
if (foldUnary(vtxp)) return;
}
void visit(DfgOneHot0* const vtxp) override {
if (foldUnary(vtxp)) return;
}
void visit(DfgRedOr* const vtxp) override {
if (optimizeReduction(vtxp)) return;
}

6
test_regress/t/t_dfg_peephole.v
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@ -62,6 +62,12 @@ 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_OneHot, $onehot(const_a));
`signal(FOLD_UNARY_OneHot0, $onehot0(const_a));
`signal(FOLD_UNARY_OneHot_A, $onehot(const_a[0]));
`signal(FOLD_UNARY_OneHot_B, $onehot(~const_a[0]));
`signal(FOLD_UNARY_OneHot0_A, $onehot0(const_a[0]));
`signal(FOLD_UNARY_OneHot0_B, $onehot0(~const_a[0]));
`signal(FOLD_BINARY_Add, const_a + const_b);
`signal(FOLD_BINARY_And, const_a & const_b);