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V3Timing: pre-clear destructive event state before dynamic waits (#7340)

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When lowering dynamic event controls, destructive pre-clear updates were inserted with addHereThisAsNext() on the original node and then that node was replaced. This could leave leaked/orphaned nodes under leak-checking runs.

Build an explicit replacement stmt chain instead:
  [pre-clear stmts] -> trigger loop -> awaitResumption,
and replace the original control with the chain head. Keep the loop-only path unchanged when no destructive pre-clear is needed.
This commit is contained in:
Nick Brereton
2026-05-12 19:01:37 +01:00
committed by GitHub
parent 67b21e4c62
commit 9588e67ca9
4 changed files with 89 additions and 19 deletions
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src/V3Timing.cpp
+19 -17
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@@ -639,15 +639,6 @@ class TimingControlVisitor final : public VNVisitor {
return !nodep->isPure();
});
}
// Returns true if the given trigger expression needs a destructive post update after trigger
// evaluation. Currently this only applies to named events.
bool destructivePostUpdate(AstNode* const exprp) const {
return exprp->exists([](const AstNode* const nodep) {
const AstNodeDType* const dtypep = nodep->dtypep();
const AstBasicDType* const basicp = dtypep ? dtypep->skipRefp()->basicp() : nullptr;
return basicp && basicp->isEvent();
});
}
// Creates a trigger scheduler variable
AstVarScope* getCreateTriggerSchedulerp(AstSenTree* const sentreep) {
if (!sentreep->user1p()) {
@@ -1085,7 +1076,6 @@ class TimingControlVisitor final : public VNVisitor {
= createTemp(flp, m_dynTrigNames.get(nodep), nodep->findBitDType(), nodep);
auto* const initp = new AstAssign{flp, new AstVarRef{flp, trigvscp, VAccess::WRITE},
new AstConst{flp, AstConst::BitFalse{}}};
nodep->addHereThisAsNext(initp);
// Await the eval step with the dynamic trigger scheduler. First, create the method
// call
auto* const evalMethodp = new AstCMethodHard{
@@ -1105,10 +1095,10 @@ class TimingControlVisitor final : public VNVisitor {
// Get the SenExprBuilder results
const SenExprBuilder::Results senResults = m_senExprBuilderp->getAndClearResults();
localizeVars(m_procp, senResults.m_vars);
// Put all and inits before the trigger eval loop
for (AstNodeStmt* const stmtp : senResults.m_inits) {
nodep->addHereThisAsNext(stmtp);
}
// If post updates are destructive (e.g. clearFired on events), perform a
// conservative pre-clear once before entering the wait loop so stale state from a
// previous wait does not cause an immediate false-positive trigger.
const bool hasDestructivePostUpdates = !senResults.m_destructivePostUpdates.empty();
// Create the trigger eval loop, which will await the evaluation step and check the
// trigger
AstNodeExpr* const condp
@@ -1129,7 +1119,7 @@ class TimingControlVisitor final : public VNVisitor {
loopp->addStmtsp(anyTriggeredMethodp->makeStmt());
// If the post update is destructive (e.g. event vars are cleared), create an await for
// the post update step
if (destructivePostUpdate(sentreep)) {
if (hasDestructivePostUpdates) {
AstCAwait* const awaitPostUpdatep = awaitEvalp->cloneTree(false);
VN_AS(awaitPostUpdatep->exprp(), CMethodHard)->method(VCMethod::SCHED_POST_UPDATE);
loopp->addStmtsp(awaitPostUpdatep);
@@ -1140,8 +1130,20 @@ class TimingControlVisitor final : public VNVisitor {
AstCAwait* const awaitResumep = awaitEvalp->cloneTree(false);
VN_AS(awaitResumep->exprp(), CMethodHard)->method(VCMethod::SCHED_RESUMPTION);
AstNode::addNext<AstNodeStmt, AstNodeStmt>(loopp, awaitResumep);
// Replace the event control with the loop
nodep->replaceWith(loopp);
// Replace the event control with one explicit stmt chain:
// init -> [inits] -> [optional destructive pre-clears] -> loop -> awaitResumption
AstNodeStmt* chainp = nullptr;
chainp = AstNode::addNextNull(chainp, initp);
for (AstNodeStmt* const stmtp : senResults.m_inits) {
chainp = AstNode::addNextNull(chainp, stmtp);
}
if (hasDestructivePostUpdates) {
for (AstNodeStmt* const stmtp : senResults.m_destructivePostUpdates) {
chainp = AstNode::addNextNull(chainp, stmtp->cloneTree(false));
}
}
chainp = AstNode::addNextNull(chainp, loopp);
nodep->replaceWith(chainp);
} else {
auto* const sentreep = m_finder.getSenTree(nodep->sentreep());
nodep->sentreep()->unlinkFrBack()->deleteTree();