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[Clang] Correctly handle allocations in the condition of a if constexpr #146890

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Merged
merged 4 commits into from
Jul 4, 2025
Merged

[Clang] Correctly handle allocations in the condition of a if constexpr #146890

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c138801
[Clang] Correctly handle allocations in the condition of a `if conste…
cor3ntin Jul 3, 2025
7d6b68a
add tests and remove bogus assert
cor3ntin Jul 3, 2025
b26b29d
more tests
cor3ntin Jul 3, 2025
c7a10ef
correctly handle dependent conditions
cor3ntin Jul 4, 2025
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10 changes: 5 additions & 5 deletions clang/lib/Sema/SemaExpr.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20628,10 +20628,8 @@ Sema::ConditionResult Sema::ActOnCondition(Scope *S, SourceLocation Loc,
break;

case ConditionKind::ConstexprIf:
// Note: this might produce a FullExpr
Cond = CheckBooleanCondition(Loc, SubExpr, true);
assert(isa<FullExpr>(Cond.get()) &&
"we should have converted this expression to a FullExpr before "
"evaluating it");
break;

case ConditionKind::Switch:
Expand All @@ -20643,10 +20641,12 @@ Sema::ConditionResult Sema::ActOnCondition(Scope *S, SourceLocation Loc,
{SubExpr}, PreferredConditionType(CK));
if (!Cond.get())
return ConditionError();
}
if (!isa<FullExpr>(Cond.get()))
} else if (Cond.isUsable() && !isa<FullExpr>(Cond.get()))
Cond = ActOnFinishFullExpr(Cond.get(), Loc, /*DiscardedValue*/ false);

if (Cond.isInvalid())
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@erichkeane erichkeane Jul 3, 2025

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Suggested change
if (Cond.isInvalid())
if (!Cond.isUsable())

Unless there is a reason that ConditionResult would be ok with a 'null' expr?

return ConditionError();

return ConditionResult(*this, nullptr, Cond,
CK == ConditionKind::ConstexprIf);
}
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8 changes: 7 additions & 1 deletion clang/test/SemaCXX/cxx2a-constexpr-dynalloc.cpp
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Expand Up @@ -252,7 +252,13 @@ struct S {
};

int f() {
if constexpr((S{}, true)) {
if constexpr((S{}, true)) { // expected-warning{{left operand of comma operator has no effect}}
return 1;
}
if constexpr(S s; (s, true)) { // expected-warning{{left operand of comma operator has no effect}}
return 1;
}
if constexpr(S s; (s, true)) { // expected-warning{{left operand of comma operator has no effect}}
return 1;
}
return 0;
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