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Add NEVERMATCH warning when an SVA sequence can never match (#8176) (#8183)

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Signed-off-by: Artur Bieniek <[email protected]>
This commit is contained in:
Artur Bieniek
2026-08-22 08:31:23 +02:00
committed by GitHub
parent cda258cbed
commit 3dbfa7708f
6 changed files with 62 additions and 7 deletions
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src/V3AssertNfa.cpp
+11 -4
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@@ -1087,7 +1087,11 @@ class SvaNfaBuilder final {
nodep->v3warn(E_UNSUPPORTED, "Unsupported: within with ranged cycle-delay operand");
return BuildResult::failWithError();
}
if (innerLen > outerLen) return buildNeverMatchIntersect(nodep, entryVtxp, isTopLevelStep);
if (innerLen > outerLen) {
return buildNeverMatchIntersect(
nodep, entryVtxp, isTopLevelStep,
"the inner sequence is longer than the outer sequence");
}
FileLine* const flp = nodep->fileline();
const int slack = outerLen - innerLen;
AstNodeExpr* innerOrp = nullptr;
@@ -1238,7 +1242,8 @@ class SvaNfaBuilder final {
// simply never matches. This is legal (matching nothing), not an error, so
// lower to a constant false rather than rejecting legal code.
BuildResult buildNeverMatchIntersect(AstNodeExpr* nodep, SvaStateVertex* entryVtxp,
bool isTopLevelStep) {
bool isTopLevelStep, const char* reason) {
nodep->v3warn(NEVERMATCH, "Sequence can never match because " << reason << ".");
AstNodeExpr* const falsep = new AstConst{nodep->fileline(), AstConst::BitFalse{}};
return buildFromLoweringTree(falsep, entryVtxp, isTopLevelStep);
}
@@ -1269,7 +1274,8 @@ class SvaNfaBuilder final {
const int hi = std::min(lhsRange.second, rhsRange.second);
if (lo > hi) {
// Disjoint length ranges share no common length -> never matches.
return buildNeverMatchIntersect(nodep, entryVtxp, isTopLevelStep);
return buildNeverMatchIntersect(nodep, entryVtxp, isTopLevelStep,
"intersect operands have no common length");
}
FileLine* const flp = nodep->fileline();
if (lo == hi) {
@@ -1599,7 +1605,8 @@ public:
if (lhsLen >= 0 && rhsLen >= 0) {
if (lhsLen != rhsLen) {
// Unequal fixed lengths share no common length -> never matches.
return buildNeverMatchIntersect(intp, entryVtxp, isTopLevelStep);
return buildNeverMatchIntersect(intp, entryVtxp, isTopLevelStep,
"intersect operands have no common length");
}
if (AstNodeExpr* const conjp
= conjoinFixedSeqs(intp->lhsp(), intp->rhsp(), intp->fileline())) {