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Internals: Cleanup case condition lifting (#7768)

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V3Begin used to lift impure case expressions. With V3LiftExpr, this is
now redundant.
This commit is contained in:
Geza Lore
2026-06-12 06:38:21 +01:00
committed by GitHub
parent 0ee25038ac
commit 4555c8b23c
4 changed files with 8 additions and 66 deletions
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src/V3Case.cpp
+4 -34
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@@ -147,7 +147,6 @@ class CaseVisitor final : public VNVisitor {
bool m_caseNoOverlapsAllCovered = false; // Proven to be synopsys parallel_case compliant
// For each possible value, the case branch we need
std::array<AstNode*, 1 << CASE_OVERLAP_WIDTH> m_valueItem;
bool m_needToClearCache = false; // Whether cache needs to be cleared
// METHODS
//! Determine whether we should check case items are complete
@@ -398,14 +397,6 @@ class CaseVisitor final : public VNVisitor {
// CASEx(cexpr,....
// -> tree of IF(msb, IF(msb-1, 11, 10)
// IF(msb-1, 01, 00))
AstNodeExpr* cexprp;
AstExprStmt* cexprStmtp = nullptr;
if (nodep->exprp()->isPure()) {
cexprp = nodep->exprp()->unlinkFrBack();
} else {
cexprStmtp = VN_AS(nodep->exprp()->unlinkFrBack(), ExprStmt);
cexprp = cexprStmtp->resultp()->cloneTreePure(false);
}
if (debug() >= 9) { // LCOV_EXCL_START
for (uint32_t i = 0; i < (1UL << m_caseWidth); ++i) {
@@ -419,14 +410,7 @@ class CaseVisitor final : public VNVisitor {
replaceCaseParallel(nodep, m_caseNoOverlapsAllCovered);
AstNode::user3ClearTree();
AstNode* ifrootp = replaceCaseFastRecurse(cexprp, m_caseWidth - 1, 0UL);
if (cexprStmtp) {
cexprStmtp->resultp()->unlinkFrBack()->deleteTree();
AstIf* const ifp = VN_AS(ifrootp, If);
cexprStmtp->resultp(ifp->condp()->unlinkFrBack());
ifp->condp(cexprStmtp);
m_needToClearCache = true;
}
AstNode* ifrootp = replaceCaseFastRecurse(nodep->exprp(), m_caseWidth - 1, 0UL);
// Case expressions can't be linked twice, so clone them
if (ifrootp && !ifrootp->user3()) ifrootp = ifrootp->cloneTree(true);
@@ -437,7 +421,6 @@ class CaseVisitor final : public VNVisitor {
nodep->unlinkFrBack();
}
VL_DO_DANGLING(nodep->deleteTree(), nodep);
VL_DO_DANGLING(cexprp->deleteTree(), cexprp);
UINFOTREE(9, ifrootp, "", "_simp");
}
@@ -446,14 +429,7 @@ class CaseVisitor final : public VNVisitor {
// -> IF((cexpr==icond1),istmts1,
// IF((EQ (AND MASK cexpr) (AND MASK icond1)
// ,istmts2, istmts3
AstNodeExpr* cexprp;
AstExprStmt* cexprStmtp = nullptr;
if (nodep->exprp()->isPure()) {
cexprp = nodep->exprp()->unlinkFrBack();
} else {
cexprStmtp = VN_AS(nodep->exprp(), ExprStmt)->unlinkFrBack();
cexprp = cexprStmtp->resultp()->cloneTreePure(false);
}
AstNodeExpr* const cexprp = nodep->exprp();
// We'll do this in two stages. First stage, convert the conditions to
// the appropriate IF AND terms.
UINFOTREE(9, nodep, "", "_comp_IN::");
@@ -518,7 +494,6 @@ class CaseVisitor final : public VNVisitor {
itemp->addCondsp(ifexprp);
}
}
VL_DO_DANGLING(cexprp->deleteTree(), cexprp);
if (!hadDefault) {
// If there was no default, add a empty one, this greatly simplifies below code
// and constant propagation will just eliminate it for us later.
@@ -582,12 +557,6 @@ class CaseVisitor final : public VNVisitor {
if (grouprootp) {
UINFOTREE(9, grouprootp, "", "_new");
nodep->replaceWith(grouprootp);
if (cexprStmtp) {
pushDeletep(cexprStmtp->resultp()->unlinkFrBack());
cexprStmtp->resultp(grouprootp->condp()->unlinkFrBack());
grouprootp->condp(cexprStmtp);
m_needToClearCache = true;
}
} else {
nodep->unlinkFrBack();
}
@@ -622,6 +591,8 @@ class CaseVisitor final : public VNVisitor {
{ CaseLintVisitor{nodep}; }
iterateChildren(nodep);
UINFOTREE(9, nodep, "", "case_old");
UASSERT_OBJ(nodep->exprp()->isPure(), nodep,
"Impure case expression should have been removed by V3LiftExpr");
if (isCaseTreeFast(nodep) && v3Global.opt.fCase()) {
// It's a simple priority encoder or complete statement
// we can make a tree of statements to avoid extra comparisons
@@ -648,7 +619,6 @@ public:
explicit CaseVisitor(AstNetlist* nodep) {
for (auto& itr : m_valueItem) itr = nullptr;
iterate(nodep);
if (m_needToClearCache) VIsCached::clearCacheTree();
}
~CaseVisitor() override {
V3Stats::addStat("Optimizations, Cases parallelized", m_statCaseFast);