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[Clang] treat fixed-underlying enum constants as the enumerated type in C23 to follow the spec #172211

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[Clang] treat fixed-underlying enum constants as the enumerated type in C23 to follow the spec #172211

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9d82454
[Clang] treat fixed-underlying enum constants as the enumerated type …
a-tarasyuk Dec 14, 2025
cef3ccf
add tests to cover c23 underlying enum member types
a-tarasyuk Dec 16, 2025
bf444ff
Merge branch 'main' of https://github.com/llvm/llvm-project into fix/…
a-tarasyuk Dec 16, 2025
594ccfe
Merge branch 'main' into fix/172118
a-tarasyuk Dec 16, 2025
89159d8
Merge branch 'main' into fix/172118
a-tarasyuk Dec 16, 2025
709e669
update tests
a-tarasyuk Dec 16, 2025
42e297b
Merge branch 'fix/172118' of https://github.com/a-tarasyuk/llvm-proje…
a-tarasyuk Dec 16, 2025
b3dad82
Merge branch 'main' of https://github.com/llvm/llvm-project into fix/…
a-tarasyuk Dec 16, 2025
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1 change: 1 addition & 0 deletions clang/docs/ReleaseNotes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -534,6 +534,7 @@ Bug Fixes in This Version
- Fixed false-positive shadow diagnostics for lambdas in explicit object member functions. (#GH163731)
- Fix an assertion failure when a ``target_clones`` attribute is only on the
forward declaration of a multiversioned function. (#GH165517) (#GH129483)
- Clang now treats enumeration constants of fixed-underlying enums as the enumerated type. (#GH172118)

Bug Fixes to Compiler Builtins
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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8 changes: 6 additions & 2 deletions clang/lib/Sema/SemaDecl.cpp
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Expand Up @@ -20814,10 +20814,12 @@ void Sema::ActOnEnumBody(SourceLocation EnumLoc, SourceRange BraceRange,
NewSign = true;
} else if (ECD->getType() == BestType) {
// Already the right type!
if (getLangOpts().CPlusPlus)
if (getLangOpts().CPlusPlus || (getLangOpts().C23 && Enum->isFixed()))
// C++ [dcl.enum]p4: Following the closing brace of an
// enum-specifier, each enumerator has the type of its
// enumeration.
// C23 6.7.2.2p15: For an enumerated type with fixed underlying type,
// the enumeration member type is the enumerated type.
ECD->setType(EnumType);
continue;
} else {
Expand All @@ -20837,10 +20839,12 @@ void Sema::ActOnEnumBody(SourceLocation EnumLoc, SourceRange BraceRange,
ECD->setInitExpr(ImplicitCastExpr::Create(
Context, NewTy, CK_IntegralCast, ECD->getInitExpr(),
/*base paths*/ nullptr, VK_PRValue, FPOptionsOverride()));
if (getLangOpts().CPlusPlus)
if (getLangOpts().CPlusPlus || (getLangOpts().C23 && Enum->isFixed()))
// C++ [dcl.enum]p4: Following the closing brace of an
// enum-specifier, each enumerator has the type of its
// enumeration.
// C23 6.7.2.2p15: For an enumerated type with fixed underlying type, the
// enumeration member type is the enumerated type.
ECD->setType(EnumType);
else
ECD->setType(NewTy);
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20 changes: 20 additions & 0 deletions clang/test/Sema/c23-switch.c
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@@ -0,0 +1,20 @@
// RUN: %clang_cc1 -std=c23 -fsyntax-only -verify -Wswitch %s

typedef enum : long { E0 } E;
void test1(E e) {
auto v = E0;
switch (v) { } // expected-warning {{enumeration value 'E0' not handled in switch}}
}

void test2(E e) {
__auto_type v = E0;
switch (v) { } // expected-warning {{enumeration value 'E0' not handled in switch}}
}

void test3(_Bool b, E e) {
__auto_type v = E0;
if (b) {
v = e;
}
switch (v) { } // expected-warning {{enumeration value 'E0' not handled in switch}}
}
6 changes: 3 additions & 3 deletions clang/test/SemaCXX/bitfield-preferred-type-sizing.cpp
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Expand Up @@ -377,9 +377,9 @@ void write_high_constantA(S_A *s) {
void write_high_constantB(S_B *s) {
s->field1 = ENUM_CLASS_REF(B, B_d);
// cpp-warning@-1 {{implicit truncation from 'B' to bit-field changes value from 3 to 1}}
// c-warning@-2 {{implicit truncation from 'int' to bit-field changes value from 3 to -1}}
// c-warning@-2 {{implicit truncation from 'enum B' to bit-field changes value from 3 to -1}}
s->field2 = ENUM_CLASS_REF(B, B_d);
// c-warning@-1 {{implicit truncation from 'int' to bit-field changes value from 3 to -1}}
// c-warning@-1 {{implicit truncation from 'enum B' to bit-field changes value from 3 to -1}}
s->field3 = ENUM_CLASS_REF(B, B_d);
s->field4 = (unsigned)ENUM_CLASS_REF(B, B_d);
// expected-warning@-1 {{implicit truncation from 'unsigned int' to bit-field changes value from 3 to 1}}
Expand All @@ -396,7 +396,7 @@ void write_high_constantB(S_B *s) {
void write_high_constantC(S_C *s) {
s->field1 = ENUM_CLASS_REF(C, C_d);
// cpp-warning@-1 {{implicit truncation from 'C' to bit-field changes value from 3 to 1}}
// c-warning@-2 {{implicit truncation from 'unsigned int' to bit-field changes value from 3 to 1}}
// c-warning@-2 {{implicit truncation from 'enum C' to bit-field changes value from 3 to 1}}
s->field2 = ENUM_CLASS_REF(C, C_d);
s->field3 = ENUM_CLASS_REF(C, C_d);
s->field4 = (unsigned)ENUM_CLASS_REF(C, C_d);
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