Do not normalize empty FoldExprs?

clang/include/clang/Sema/Sema.h

@@ -13339,7 +13339,7 @@ class Sema final : public SemaBase {
   bool SubstTemplateArgumentsInParameterMapping(
       ArrayRef<TemplateArgumentLoc> Args, SourceLocation BaseLoc,
       const MultiLevelTemplateArgumentList &TemplateArgs,
-      TemplateArgumentListInfo &Out);
+      TemplateArgumentListInfo &Out, bool BuildPackExpansionTypes);
 
   /// Retrieve the template argument list(s) that should be used to
   /// instantiate the definition of the given declaration.
@@ -13799,15 +13799,15 @@ class Sema final : public SemaBase {
   }
 
   /// Determine whether we are currently performing constraint substitution.
-  // FIXME: Rename it
   bool inConstraintSubstitution() const {
     return !CodeSynthesisContexts.empty() &&
            CodeSynthesisContexts.back().InConstraintSubstitution;
   }
 
   bool inParameterMappingSubstitution() const {
     return !CodeSynthesisContexts.empty() &&
-           CodeSynthesisContexts.back().InParameterMappingSubstitution;
+           CodeSynthesisContexts.back().InParameterMappingSubstitution &&
+           !inConstraintSubstitution();
   }
 
   using EntityPrinter = llvm::function_ref<void(llvm::raw_ostream &)>;
@@ -14819,6 +14819,9 @@ class Sema final : public SemaBase {
       const NamedDecl *D1, ArrayRef<AssociatedConstraint> AC1,
       const NamedDecl *D2, ArrayRef<AssociatedConstraint> AC2);
 
+  llvm::DenseMap<unsigned, CachedConceptIdConstraint>
+      ConceptIdSatisfactionCache;
+
 private:
   /// Caches pairs of template-like decls whose associated constraints were
   /// checked for subsumption and whether or not the first's constraints did in

clang/include/clang/Sema/SemaConcept.h

@@ -19,6 +19,7 @@
 #include "clang/AST/ExprConcepts.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/UnsignedOrNone.h"
+#include "clang/Sema/Ownership.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/STLForwardCompat.h"
@@ -67,7 +68,7 @@ struct NormalizedConstraint {
     unsigned Kind : 5;
     unsigned Placeholder : 1;
     unsigned PackSubstitutionIndex : 26;
-    llvm::SmallBitVector Indexes;
+    OccurenceList Indexes;
     TemplateArgumentLoc *Args;
     TemplateParameterList *ParamList;
     ExprOrConcept ConstraintExpr;
@@ -84,6 +85,7 @@ struct NormalizedConstraint {
     TemplateArgumentLoc *Args;
     TemplateParameterList *ParamList;
     const Expr *Pattern;
+    const NamedDecl *ConstraintDecl;
     NormalizedConstraint *Constraint;
   };
 
@@ -128,14 +130,16 @@ struct NormalizedConstraint {
                ConstraintDecl} {}
 
   NormalizedConstraint(const Expr *Pattern, FoldOperatorKind OpKind,
-                       NormalizedConstraint *Constraint)
+                       NormalizedConstraint *Constraint,
+                       const NamedDecl *ConstraintDecl)
       : FoldExpanded{llvm::to_underlying(ConstraintKind::FoldExpanded),
                      llvm::to_underlying(OpKind),
                      /*Placeholder=*/0,
                      /*Indexes=*/{},
                      /*Args=*/nullptr,
                      /*ParamList=*/nullptr,
                      Pattern,
+                     ConstraintDecl,
                      Constraint} {}
 
   NormalizedConstraint(const ConceptReference *ConceptId,
@@ -323,14 +327,17 @@ class AtomicConstraint : public NormalizedConstraintWithParamMapping {
   }
 };
 
-class FoldExpandedConstraint : public NormalizedConstraint {
-  using NormalizedConstraint::NormalizedConstraint;
+class FoldExpandedConstraint : public NormalizedConstraintWithParamMapping {
+  using NormalizedConstraintWithParamMapping::
+      NormalizedConstraintWithParamMapping;
 
 public:
   static FoldExpandedConstraint *Create(ASTContext &Ctx, const Expr *Pattern,
+                                        const NamedDecl *ConstraintDecl,
                                         FoldOperatorKind OpKind,
                                         NormalizedConstraint *Constraint) {
-    return new (Ctx) FoldExpandedConstraint(Pattern, OpKind, Constraint);
+    return new (Ctx)
+        FoldExpandedConstraint(Pattern, OpKind, Constraint, ConstraintDecl);
   }
 
   using NormalizedConstraint::hasMatchingParameterMapping;
@@ -383,6 +390,11 @@ class ConceptIdConstraint : public NormalizedConstraintWithParamMapping {
   NormalizedConstraint &getNormalizedConstraint() { return *ConceptId.Sub; }
 };
 
+struct CachedConceptIdConstraint {
+  ExprResult SubstExpr;
+  ConstraintSatisfaction Satisfaction;
+};
+
 /// \brief SubsumptionChecker establishes subsumption
 /// between two set of constraints.
 class SubsumptionChecker {
@@ -482,6 +494,6 @@ class SubsumptionChecker {
   uint16_t getNewLiteralId();
 };
 
-} // clang
+} // namespace clang
 
 #endif // LLVM_CLANG_SEMA_SEMACONCEPT_H