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[clang] Fix potential constant expression checking with constexpr-unknown. #149227

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Merged
merged 2 commits into from
Jul 17, 2025
Merged

[clang] Fix potential constant expression checking with constexpr-unknown. #149227

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9ce04c8
[clang] Fix potential constant expression checking with constexpr-unk…
efriedma-quic Jul 16, 2025
05e1a7d
Note bug numbers in tests.
efriedma-quic Jul 17, 2025
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11 changes: 7 additions & 4 deletions clang/lib/AST/ExprConstant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4450,7 +4450,8 @@ static CompleteObject findCompleteObject(EvalInfo &Info, const Expr *E,
}
} else if (!IsAccess) {
return CompleteObject(LVal.getLValueBase(), nullptr, BaseType);
} else if (IsConstant && Info.checkingPotentialConstantExpression() &&
} else if ((IsConstant || BaseType->isReferenceType()) &&
Info.checkingPotentialConstantExpression() &&
BaseType->isLiteralType(Info.Ctx) && !VD->hasDefinition()) {
// This variable might end up being constexpr. Don't diagnose it yet.
} else if (IsConstant) {
Expand Down Expand Up @@ -4491,9 +4492,11 @@ static CompleteObject findCompleteObject(EvalInfo &Info, const Expr *E,
// a null BaseVal. Any constexpr-unknown variable seen here is an error:
// we can't access a constexpr-unknown object.
if (AK != clang::AK_Dereference && !BaseVal) {
Info.FFDiag(E, diag::note_constexpr_access_unknown_variable, 1)
<< AK << VD;
Info.Note(VD->getLocation(), diag::note_declared_at);
if (!Info.checkingPotentialConstantExpression()) {
Info.FFDiag(E, diag::note_constexpr_access_unknown_variable, 1)
<< AK << VD;
Info.Note(VD->getLocation(), diag::note_declared_at);
}
return CompleteObject();
}
} else if (DynamicAllocLValue DA = LVal.Base.dyn_cast<DynamicAllocLValue>()) {
Expand Down
26 changes: 26 additions & 0 deletions clang/test/SemaCXX/constant-expression-p2280r4.cpp
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Expand Up @@ -357,3 +357,29 @@ namespace pointer_comparisons {
static_assert(!f4()); // expected-error {{static assertion expression is not an integral constant expression}} \
// expected-note {{in call to 'f4()'}}
}

namespace GH149188 {
namespace enable_if_1 {
template <__SIZE_TYPE__ N>
constexpr void foo(const char (&Str)[N])
__attribute((enable_if(__builtin_strlen(Str), ""))) {}

void x() {
foo("1234");
}
}

namespace enable_if_2 {
constexpr const char (&f())[];
extern const char (&Str)[];
constexpr int foo()
__attribute((enable_if(__builtin_strlen(Str), "")))
{return __builtin_strlen(Str);}

constexpr const char (&f())[] {return "a";}
constexpr const char (&Str)[] = f();
void x() {
constexpr int x = foo();
}
}
Comment on lines +362 to +384
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Can you reference the issue (either a comment or in the namespace name)?

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We normally use the namespace name, I think we should stick w/ that.

}
7 changes: 7 additions & 0 deletions clang/test/SemaCXX/constexpr-never-constant.cpp
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Expand Up @@ -24,3 +24,10 @@ constexpr void other_func() {

throw 12;
}

namespace GH149041 {
// Make sure these don't trigger the diagnostic.
extern const bool& b;
constexpr bool fun1() { return b; }
constexpr bool fun2(const bool& b) { return b; }
}
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