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[clang] simplify constant template parameter type deduction for partial ordering #160433

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Sep 25, 2025
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[clang] simplify constant template parameter type deduction for partial ordering #160433

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27 changes: 5 additions & 22 deletions clang/lib/Sema/SemaTemplateDeduction.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -483,7 +483,7 @@ DeduceNonTypeTemplateArgument(Sema &S, TemplateParameterList *TemplateParams,
return TemplateDeductionResult::Inconsistent;
}
Deduced[NTTP.getIndex()] = Result;
if (!S.getLangOpts().CPlusPlus17)
if (!S.getLangOpts().CPlusPlus17 && !PartialOrdering)
return TemplateDeductionResult::Success;

if (NTTP.isExpandedParameterPack())
Expand Down Expand Up @@ -2652,28 +2652,11 @@ DeduceTemplateArguments(Sema &S, TemplateParameterList *TemplateParams,
getDeducedNTTParameterFromExpr(Info, P.getAsExpr())) {
switch (A.getKind()) {
case TemplateArgument::Expression: {
const Expr *E = A.getAsExpr();
// When checking NTTP, if either the parameter or the argument is
// dependent, as there would be otherwise nothing to deduce, we force
// the argument to the parameter type using this dependent implicit
// cast, in order to maintain invariants. Now we can deduce the
// resulting type from the original type, and deduce the original type
// against the parameter we are checking.
if (const auto *ICE = dyn_cast<ImplicitCastExpr>(E);
ICE && ICE->getCastKind() == clang::CK_Dependent) {
E = ICE->getSubExpr();
if (auto Result = DeduceTemplateArgumentsByTypeMatch(
S, TemplateParams, ICE->getType(), E->getType(), Info,
Deduced, TDF_SkipNonDependent,
PartialOrdering ? PartialOrderingKind::NonCall
: PartialOrderingKind::None,
/*DeducedFromArrayBound=*/false, HasDeducedAnyParam);
Result != TemplateDeductionResult::Success)
return Result;
}
// The type of the value is the type of the expression as written.
return DeduceNonTypeTemplateArgument(
S, TemplateParams, NTTP, DeducedTemplateArgument(A), E->getType(),
Info, PartialOrdering, Deduced, HasDeducedAnyParam);
S, TemplateParams, NTTP, DeducedTemplateArgument(A),
A.getAsExpr()->IgnoreImplicitAsWritten()->getType(), Info,
PartialOrdering, Deduced, HasDeducedAnyParam);
}
case TemplateArgument::Integral:
case TemplateArgument::StructuralValue:
Expand Down