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[clang] Check constexpr int->enum conversions consistently. #143034

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Merged
merged 2 commits into from
Jun 6, 2025
Merged

[clang] Check constexpr int->enum conversions consistently. #143034

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818f2cf
[clang] Check constexpr int->enum conversions consistently.
efriedma-quic Jun 5, 2025
189674e
Fix test failure
efriedma-quic Jun 6, 2025
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20 changes: 3 additions & 17 deletions clang/lib/AST/ExprConstant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15245,21 +15245,7 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
return Info.Ctx.getTypeSize(DestType) == Info.Ctx.getTypeSize(SrcType);
}

if (Info.Ctx.getLangOpts().CPlusPlus && Info.InConstantContext &&
Info.EvalMode == EvalInfo::EM_ConstantExpression &&
DestType->isEnumeralType()) {

bool ConstexprVar = true;

// We know if we are here that we are in a context that we might require
// a constant expression or a context that requires a constant
// value. But if we are initializing a value we don't know if it is a
// constexpr variable or not. We can check the EvaluatingDecl to determine
// if it constexpr or not. If not then we don't want to emit a diagnostic.
if (const auto *VD = dyn_cast_or_null<VarDecl>(
Info.EvaluatingDecl.dyn_cast<const ValueDecl *>()))
ConstexprVar = VD->isConstexpr();

if (Info.Ctx.getLangOpts().CPlusPlus && DestType->isEnumeralType()) {
const EnumType *ET = dyn_cast<EnumType>(DestType.getCanonicalType());
const EnumDecl *ED = ET->getDecl();
// Check that the value is within the range of the enumeration values.
Expand All @@ -15279,13 +15265,13 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
ED->getValueRange(Max, Min);
--Max;

if (ED->getNumNegativeBits() && ConstexprVar &&
if (ED->getNumNegativeBits() &&
(Max.slt(Result.getInt().getSExtValue()) ||
Min.sgt(Result.getInt().getSExtValue())))
Info.CCEDiag(E, diag::note_constexpr_unscoped_enum_out_of_range)
<< llvm::toString(Result.getInt(), 10) << Min.getSExtValue()
<< Max.getSExtValue() << ED;
else if (!ED->getNumNegativeBits() && ConstexprVar &&
else if (!ED->getNumNegativeBits() &&
Max.ult(Result.getInt().getZExtValue()))
Info.CCEDiag(E, diag::note_constexpr_unscoped_enum_out_of_range)
<< llvm::toString(Result.getInt(), 10) << Min.getZExtValue()
Expand Down
7 changes: 7 additions & 0 deletions clang/test/SemaCXX/constant-expression-cxx11.cpp
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Expand Up @@ -2513,6 +2513,9 @@ void testValueInRangeOfEnumerationValues() {
// expected-error@-1 {{constexpr variable 'x2' must be initialized by a constant expression}}
// expected-note@-2 {{integer value 8 is outside the valid range of values [-8, 7] for the enumeration type 'E1'}}
E1 x2b = static_cast<E1>(8); // ok, not a constant expression context
static_assert(static_cast<E1>(8), "");
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I guess these are the cases my previous checks missed?

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Yes. The static_assert case wasn't emitting an error because of the Info.EvalMode == EvalInfo::EM_ConstantExpression check. The "neg_one_constexpr" case wasn't emitting an error because of the ConstexprVar check.

(Looking again, I guess I could have also come up with a separate testcase for the InConstantContext check, but I didn't really think too deeply about it.)

// expected-error@-1 {{static assertion expression is not an integral constant expression}}
// expected-note@-2 {{integer value 8 is outside the valid range of values [-8, 7] for the enumeration type 'E1'}}

constexpr E2 x3 = static_cast<E2>(-8);
// expected-error@-1 {{constexpr variable 'x3' must be initialized by a constant expression}}
Expand Down Expand Up @@ -2551,6 +2554,10 @@ void testValueInRangeOfEnumerationValues() {
// expected-note@-2 {{integer value 2147483648 is outside the valid range of values [-2147483648, 2147483647] for the enumeration type 'EMaxInt'}}

const NumberType neg_one = (NumberType) ((NumberType) 0 - (NumberType) 1); // ok, not a constant expression context
constexpr NumberType neg_one_constexpr = neg_one;
// expected-error@-1 {{constexpr variable 'neg_one_constexpr' must be initialized by a constant expression}}
// expected-note@-2 {{initializer of 'neg_one' is not a constant expression}}
// expected-note@-4 {{declared here}}

CONSTEXPR_CAST_TO_SYSTEM_ENUM_OUTSIDE_OF_RANGE;
// expected-error@-1 {{constexpr variable 'system_enum' must be initialized by a constant expression}}
Expand Down