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Optimize Dfg with relaxed live variable analysis (#7739)

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Relax the live variable analysis performed by Dfg to bail on fewer
cases. This analysis was already conservative (meaning it might think
variables are live when they are not), which is good enough for Dfg use.
This change in particular enables synthesizing more complex logic
involving arrays, e.g. those introduce by V3Table creating lookup
tables.
This commit is contained in:
Geza Lore
2026-06-10 15:59:44 +01:00
committed by GitHub
parent 75993ca9ea
commit d84af81a11
6 changed files with 30 additions and 26 deletions
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src/V3Dfg.cpp
+6 -3
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@@ -906,17 +906,20 @@ AstScope* DfgVertex::scopep(ScopeCache& cache, bool tryResultVar) VL_MT_DISABLED
}
}
AstScope* const rootp = v3Global.rootp()->topScopep()->scopep();
AstScope* const constPoolp = v3Global.rootp()->constPoolp()->scopep();
// Note: the recursive invocation can cause a re-hash but that will not invalidate references
AstScope*& resultr = cache[this];
if (!resultr) {
// Mark to prevent infinite recursion on circular graphs - should never be called on such
resultr = reinterpret_cast<AstScope*>(1);
// Find scope based on sources, falling back on the root scope
AstScope* const rootp = v3Global.rootp()->topScopep()->scopep();
// Find scope based on sources, falling back on the root scope,
// also make sure it's not the constant pool scope, which is special.
AstScope* foundp = nullptr;
foreachSource([&](DfgVertex& src) {
AstScope* const scp = src.scopep(cache, true);
if (scp != rootp) {
if (scp != rootp && scp != constPoolp) {
foundp = scp;
return true;
}