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[Clang] Give empty template parameter mapping an empty MLTAL #164051

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zyn0217 merged 5 commits into from
Oct 20, 2025
Merged

[Clang] Give empty template parameter mapping an empty MLTAL #164051

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1c34050
[Clang] Give empty template parameter mapping an empty MLTAL
zyn0217 Oct 18, 2025
9beea6e
NFC: Fix spelling: OuterMost -> Outermost
zyn0217 Oct 18, 2025
6768cec
Add test
zyn0217 Oct 18, 2025
ca33e1a
Revert "NFC: Fix spelling: OuterMost -> Outermost"
zyn0217 Oct 19, 2025
23ec536
Address feedback
zyn0217 Oct 19, 2025
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52 changes: 33 additions & 19 deletions clang/lib/Sema/SemaConcept.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -432,7 +432,7 @@ class ConstraintSatisfactionChecker {
// XXX: It is SLOW! Use it very carefully.
std::optional<MultiLevelTemplateArgumentList> SubstitutionInTemplateArguments(
const NormalizedConstraintWithParamMapping &Constraint,
MultiLevelTemplateArgumentList MLTAL,
const MultiLevelTemplateArgumentList &MLTAL,
llvm::SmallVector<TemplateArgument> &SubstitutedOuterMost);

ExprResult EvaluateSlow(const AtomicConstraint &Constraint,
Expand Down Expand Up @@ -564,12 +564,17 @@ ExprResult ConstraintSatisfactionChecker::EvaluateAtomicConstraint(
std::optional<MultiLevelTemplateArgumentList>
ConstraintSatisfactionChecker::SubstitutionInTemplateArguments(
const NormalizedConstraintWithParamMapping &Constraint,
MultiLevelTemplateArgumentList MLTAL,
llvm::SmallVector<TemplateArgument> &SubstitutedOuterMost) {
const MultiLevelTemplateArgumentList &MLTAL,
llvm::SmallVector<TemplateArgument> &SubstitutedOutermost) {

if (!Constraint.hasParameterMapping())
return std::move(MLTAL);

// The mapping is empty, meaning no template arguments are needed for
// evaluation.
if (Constraint.getParameterMapping().empty())
return MultiLevelTemplateArgumentList();

TemplateDeductionInfo Info(Constraint.getBeginLoc());
Sema::InstantiatingTemplate Inst(
S, Constraint.getBeginLoc(),
Expand Down Expand Up @@ -607,27 +612,27 @@ ConstraintSatisfactionChecker::SubstitutionInTemplateArguments(
// The empty MLTAL situation should only occur when evaluating non-dependent
// constraints.
if (MLTAL.getNumSubstitutedLevels())
SubstitutedOuterMost =
SubstitutedOutermost =
llvm::to_vector_of<TemplateArgument>(MLTAL.getOutermost());
unsigned Offset = 0;
for (unsigned I = 0, MappedIndex = 0; I < Used.size(); I++) {
TemplateArgument Arg;
if (Used[I])
Arg = S.Context.getCanonicalTemplateArgument(
CTAI.SugaredConverted[MappedIndex++]);
if (I < SubstitutedOuterMost.size()) {
SubstitutedOuterMost[I] = Arg;
if (I < SubstitutedOutermost.size()) {
SubstitutedOutermost[I] = Arg;
Offset = I + 1;
} else {
SubstitutedOuterMost.push_back(Arg);
Offset = SubstitutedOuterMost.size();
SubstitutedOutermost.push_back(Arg);
Offset = SubstitutedOutermost.size();
}
}
if (Offset < SubstitutedOuterMost.size())
SubstitutedOuterMost.erase(SubstitutedOuterMost.begin() + Offset);
if (Offset < SubstitutedOutermost.size())
SubstitutedOutermost.erase(SubstitutedOutermost.begin() + Offset);

MultiLevelTemplateArgumentList SubstitutedTemplateArgs;
SubstitutedTemplateArgs.addOuterTemplateArguments(TD, SubstitutedOuterMost,
SubstitutedTemplateArgs.addOuterTemplateArguments(TD, SubstitutedOutermost,
/*Final=*/false);
return std::move(SubstitutedTemplateArgs);
}
Expand All @@ -636,9 +641,9 @@ ExprResult ConstraintSatisfactionChecker::EvaluateSlow(
const AtomicConstraint &Constraint,
const MultiLevelTemplateArgumentList &MLTAL) {

llvm::SmallVector<TemplateArgument> SubstitutedOuterMost;
llvm::SmallVector<TemplateArgument> SubstitutedOutermost;
std::optional<MultiLevelTemplateArgumentList> SubstitutedArgs =
SubstitutionInTemplateArguments(Constraint, MLTAL, SubstitutedOuterMost);
SubstitutionInTemplateArguments(Constraint, MLTAL, SubstitutedOutermost);
if (!SubstitutedArgs) {
Satisfaction.IsSatisfied = false;
return ExprEmpty();
Expand Down Expand Up @@ -786,13 +791,13 @@ ExprResult ConstraintSatisfactionChecker::EvaluateSlow(
FoldExpandedConstraint::FoldOperatorKind::And;
unsigned EffectiveDetailEndIndex = Satisfaction.Details.size();

llvm::SmallVector<TemplateArgument> SubstitutedOuterMost;
llvm::SmallVector<TemplateArgument> SubstitutedOutermost;
// FIXME: Is PackSubstitutionIndex correct?
llvm::SaveAndRestore _(PackSubstitutionIndex, S.ArgPackSubstIndex);
std::optional<MultiLevelTemplateArgumentList> SubstitutedArgs =
SubstitutionInTemplateArguments(
static_cast<const NormalizedConstraintWithParamMapping &>(Constraint),
MLTAL, SubstitutedOuterMost);
MLTAL, SubstitutedOutermost);
if (!SubstitutedArgs) {
Satisfaction.IsSatisfied = false;
return ExprError();
Expand Down Expand Up @@ -880,9 +885,9 @@ ExprResult ConstraintSatisfactionChecker::EvaluateSlow(
const MultiLevelTemplateArgumentList &MLTAL, unsigned Size) {
const ConceptReference *ConceptId = Constraint.getConceptId();

llvm::SmallVector<TemplateArgument> SubstitutedOuterMost;
llvm::SmallVector<TemplateArgument> SubstitutedOutermost;
std::optional<MultiLevelTemplateArgumentList> SubstitutedArgs =
SubstitutionInTemplateArguments(Constraint, MLTAL, SubstitutedOuterMost);
SubstitutionInTemplateArguments(Constraint, MLTAL, SubstitutedOutermost);

if (!SubstitutedArgs) {
Satisfaction.IsSatisfied = false;
Expand Down Expand Up @@ -2017,8 +2022,13 @@ void SubstituteParameterMappings::buildParameterMapping(
SemaRef.MarkUsedTemplateParameters(Args->arguments(),
/*Depth=*/0, OccurringIndices);
}
unsigned Size = OccurringIndices.count();
// It's OK when Size is 0. We build an empty parameter mapping when the atomic
// constraint is independent of any template parameters, so we can distinguish
// it from cases where no mapping exists at all, e.g. when there are only
// atomic constraints.
TemplateArgumentLoc *TempArgs =
new (SemaRef.Context) TemplateArgumentLoc[OccurringIndices.count()];
new (SemaRef.Context) TemplateArgumentLoc[Size];
llvm::SmallVector<NamedDecl *> UsedParams;
for (unsigned I = 0, J = 0, C = TemplateParams->size(); I != C; ++I) {
SourceLocation Loc = ArgsAsWritten->NumTemplateArgs > I
Expand All @@ -2039,7 +2049,6 @@ void SubstituteParameterMappings::buildParameterMapping(
TemplateParams->getLAngleLoc(), UsedParams,
/*RAngleLoc=*/SourceLocation(),
/*RequiresClause=*/nullptr);
unsigned Size = OccurringIndices.count();
N.updateParameterMapping(
std::move(OccurringIndices), std::move(OccurringIndicesForSubsumption),
MutableArrayRef<TemplateArgumentLoc>{TempArgs, Size}, UsedList);
Expand All @@ -2050,6 +2059,11 @@ bool SubstituteParameterMappings::substitute(
if (!N.hasParameterMapping())
buildParameterMapping(N);

// Don't bother into substituting if we have determined the mapping maps to
// nothing.
if (N.getParameterMapping().empty())
return false;

SourceLocation InstLocBegin, InstLocEnd;
llvm::ArrayRef Arguments = ArgsAsWritten->arguments();
if (Arguments.empty()) {
Expand Down
18 changes: 18 additions & 0 deletions clang/test/SemaTemplate/concepts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1441,6 +1441,24 @@ void main() { Feeder<int>{}.feed<Cat<int>>(); }

}

namespace case9 {

template <typename>
concept a = requires { requires true; };
template <typename T>
concept b = a<typename T::EntitySpec>;
template <typename T>
concept c = requires { b<T>; };
template <typename T>
requires c<T>
struct s;
template <typename> constexpr bool f() { return true; }
template <typename T> constexpr bool d = f<T>();
struct s2;
static_assert(d<s<s2>>);

}

}

namespace GH162125 {
Expand Down