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Extend life of variables in DiagComparison in ExprConstant #79522

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Extend life of variables in DiagComparison in ExprConstant #79522

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Extend life of variables in `DiagComparison` in `ExprConstant`
Jan 25, 2024
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Jan 26, 2024
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20 changes: 17 additions & 3 deletions clang/lib/AST/ExprConstant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13288,9 +13288,23 @@ EvaluateComparisonBinaryOperator(EvalInfo &Info, const BinaryOperator *E,
// Reject differing bases from the normal codepath; we special-case
// comparisons to null.
if (!HasSameBase(LHSValue, RHSValue)) {
auto DiagComparison = [&] (unsigned DiagID, bool Reversed = false) {
std::string LHS = LHSValue.toString(Info.Ctx, E->getLHS()->getType());
std::string RHS = RHSValue.toString(Info.Ctx, E->getRHS()->getType());
auto DiagComparison = [&](unsigned DiagID, bool Reversed = false) {
static std::string LHS, RHS;
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They are not const, how can we make them static?

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They are not const, but we update their value every time visiting the function. Assigning value is moved to the next line, which is executed every time.

It is a workaround, but I'm unsure if a good one. (However, it solved the problem with buildbots.)
Code suggested by @cor3ntin works as well for a reason I don't understand.
It's more confusing than I initially thought.

// FIXME: To prevent the use of variables beyond their lifetime, we have
// made them static. However, this approach may not fully address the
// underlying issue. StringRef objects (made from those strings) can
// potentially change their contents unexpectedly.
// Or potentially use of freed memory may happen. Therefore, further
// investigation is required to ensure that making those variables
// static effectively resolves the problem.
// We should investigate why buildbots were failing with ASan short
// string annotations turned on. Related PR:
// https://github.com/llvm/llvm-project/pull/79049
// If making those variables static didn't fix the problem,
// please confirm that https://github.com/llvm/llvm-project/pull/79489
// fixed the real issue.
LHS = LHSValue.toString(Info.Ctx, E->getLHS()->getType());
RHS = RHSValue.toString(Info.Ctx, E->getRHS()->getType());
Info.FFDiag(E, DiagID)
<< (Reversed ? RHS : LHS) << (Reversed ? LHS : RHS);
return false;
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