Switch to checking EvaluationContext

Author: zyn0217

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -4829,8 +4829,8 @@ TemplateDeductionResult Sema::DeduceTemplateArguments(
                                           /*AdjustExceptionSpec*/false);
 
   // Unevaluated SFINAE context.
-  EnterExpressionEvaluationContext Unevaluated(
-      *this, Sema::ExpressionEvaluationContext::Unevaluated);
+  std::optional<EnterExpressionEvaluationContext> Unevaluated(
+      std::in_place, *this, Sema::ExpressionEvaluationContext::Unevaluated);
   SFINAETrap Trap(*this);
 
   Deduced.resize(TemplateParams->size());
@@ -4873,13 +4873,14 @@ TemplateDeductionResult Sema::DeduceTemplateArguments(
       DeduceReturnType(Specialization, Info.getLocation(), false))
     return TemplateDeductionResult::MiscellaneousDeductionFailure;
 
+  Unevaluated = std::nullopt;
   // [C++26][expr.const]/p17
   // An expression or conversion is immediate-escalating if it is not initially
   // in an immediate function context and it is [...]
   // a potentially-evaluated id-expression that denotes an immediate function.
   if (IsAddressOfFunction && getLangOpts().CPlusPlus20 &&
       Specialization->isImmediateEscalating() &&
-      parentEvaluationContext().isPotentiallyEvaluated() &&
+      currentEvaluationContext().isPotentiallyEvaluated() &&
       CheckIfFunctionSpecializationIsImmediate(Specialization,
                                                Info.getLocation()))
     return TemplateDeductionResult::MiscellaneousDeductionFailure;

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -5836,8 +5836,11 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
   // With CWG2369, we substitute constraints before instantiating the associated
   // function template. This helps prevent potential code generation for
   // dependent types, particularly under the MS ABI.
-  if (!inConstraintSubstitution() ||
-      !getLambdaAwareParentOfDeclContext(Function)->isDependentContext()) {
+  bool InUnevaluatedOrImmediateContext =
+      llvm::any_of(ExprEvalContexts, [](auto &Context) {
+        return Context.isUnevaluated() || Context.isImmediateFunctionContext();
+      });
+  if (!InUnevaluatedOrImmediateContext) {
     DeclGroupRef DG(Function);
     Consumer.HandleTopLevelDecl(DG);
   }

clang/test/CodeGenCXX/ms-mangle-requires.cpp

@@ -14,7 +14,7 @@ concept is_derived_from_optional =
     requires(Tp param) { []<class Up>(Up) {}(param); };
 
 template <class Tp, class Up>
-  requires(is_derived_from_optional<Up>)
+  requires(is_derived_from_optional<Up> && []<class W>(W) { return true; }(Up()))
 compare_three_way_result_t<Tp, Up> operator<=>(Tp, Up);
 
 struct RuntimeModeArgs {