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Fix bad assertion in DFG variable elimination

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Fixes #4943
This commit is contained in:
Geza Lore
2024-03-05 18:51:46 +00:00
parent 97db128d66
commit 3a1355fb54
4 changed files with 54 additions and 25 deletions
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src/V3DfgPasses.cpp
+17 -24
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@@ -274,8 +274,10 @@ void V3DfgPasses::eliminateVars(DfgGraph& dfg, V3DfgEliminateVarsContext& ctx) {
workListp = &vtx;
};
// Variable replacements to apply in the module
std::unordered_map<AstVar*, AstVar*> replacements;
// List of variables we are replacing
std::vector<AstVar*> replacedVariables;
// AstVar::user1p() : AstVar* -> The replacement variables
const VNUser1InUse user1InUse;
// Process the work list
while (workListp != sentinelp) {
@@ -315,24 +317,16 @@ void V3DfgPasses::eliminateVars(DfgGraph& dfg, V3DfgEliminateVarsContext& ctx) {
++ctx.m_varsRemoved;
varp->replaceWith(varp->source(0));
varp->varp()->unlinkFrBack()->deleteTree();
} else if (DfgVarPacked* const canonp = varp->source(0)->cast<DfgVarPacked>()) {
// If it's driven from another canonical variable, it can be replaced by that.
// However, we don't want to propagate SystemC variables into the design
if (canonp->varp()->isSc()) continue;
// Note that if this is a duplicate variable, then the canonical variable must
// be either kept or have module references. We ensured this earlier when picking
// the canonical variable in the regularize pass. Additionally, it's possible
// neither of those holds, if an otherwise unreferenced variable drives another one.
// In that case it's true that it must not have a source, so it cannot itself be
// substituted. This condition can be relaxed if needed by supporting recursive
// substitution below.
UASSERT_OBJ(canonp->keep() || canonp->hasDfgRefs() || canonp->hasModRefs()
|| !canonp->isDrivenByDfg(),
varp, "Canonical variable should be kept or have module refs");
} else if (DfgVarPacked* const driverp = varp->source(0)->cast<DfgVarPacked>()) {
// If it's driven from another variable, it can be replaced by that. However, we do not
// want to propagate SystemC variables into the design.
if (driverp->varp()->isSc()) continue;
// Mark it for replacement
++ctx.m_varsReplaced;
UASSERT_OBJ(!varp->hasSinks(), varp, "Variable inlining should make this impossible");
const bool newEntry = replacements.emplace(varp->varp(), canonp->varp()).second;
UASSERT_OBJ(newEntry, varp->varp(), "Replacement already exists");
UASSERT(!varp->varp()->user1p(), "Replacement already exists");
replacedVariables.emplace_back(varp->varp());
varp->varp()->user1p(driverp->varp());
} else {
// Otherwise this *is* the canonical var
continue;
@@ -345,19 +339,18 @@ void V3DfgPasses::eliminateVars(DfgGraph& dfg, V3DfgEliminateVarsContext& ctx) {
}
// Job done if no replacements possible
if (replacements.empty()) return;
if (replacedVariables.empty()) return;
// Apply variable replacements in the module
VNDeleter deleter;
dfg.modulep()->foreach([&](AstVarRef* refp) {
const auto it = replacements.find(refp->varp());
if (it == replacements.end()) return;
refp->replaceWith(new AstVarRef{refp->fileline(), it->second, refp->access()});
deleter.pushDeletep(refp);
AstVar* varp = refp->varp();
while (AstVar* const replacementp = VN_AS(varp->user1p(), Var)) varp = replacementp;
refp->varp(varp);
});
// Remove the replaced variables
for (const auto& pair : replacements) pair.first->unlinkFrBack()->deleteTree();
for (AstVar* const varp : replacedVariables) varp->unlinkFrBack()->deleteTree();
}
void V3DfgPasses::optimize(DfgGraph& dfg, V3DfgOptimizationContext& ctx) {