Revert "Deferred Concept Instantiation Implementation"

This reverts commit 4b6c2cd647.

The patch caused numerous ARM 32 bit build failures, since we added a
5th item to the PointerUnion, and went over the 2-bits available in the
32 bit pointers.

clang/docs/ReleaseNotes.rst

@@ -275,10 +275,6 @@ C++20 Feature Support
   `Issue 54578 <https://github.com/llvm/llvm-project/issues/54578>`_.
 
 - Implemented `__builtin_source_location()` which enables library support for std::source_location.
-- Clang now correctly delays the instantiation of function constraints until
-  the time of checking, which should now allow the libstdc++ ranges implementation
-  to work for at least trivial examples.  This fixes
-  `Issue 44178 <https://github.com/llvm/llvm-project/issues/44178>`_.
 
 - The mangling scheme for C++20 modules has incompatibly changed. The
   initial mangling was discovered not to be reversible, and the weak

clang/include/clang/AST/Decl.h

@@ -1890,9 +1890,7 @@ public:
     TK_FunctionTemplateSpecialization,
     // A function template specialization that hasn't yet been resolved to a
     // particular specialized function template.
-    TK_DependentFunctionTemplateSpecialization,
+    TK_DependentFunctionTemplateSpecialization
-    // A non templated function which is in a dependent scope.
-    TK_DependentNonTemplate
   };
 
   /// Stashed information about a defaulted function definition whose body has
@@ -1941,17 +1939,16 @@ private:
   /// The template or declaration that this declaration
   /// describes or was instantiated from, respectively.
   ///
-  /// For non-templates this value will be NULL, unless this non-template
+  /// For non-templates, this value will be NULL. For function
-  /// function declaration was declared directly inside of a function template,
+  /// declarations that describe a function template, this will be a
-  /// in which case this will have a pointer to a FunctionDecl. For function
+  /// pointer to a FunctionTemplateDecl. For member functions
-  /// declarations that describe a function template, this will be a pointer to
+  /// of class template specializations, this will be a MemberSpecializationInfo
-  /// a FunctionTemplateDecl. For member functions of class template
+  /// pointer containing information about the specialization.
-  /// specializations, this will be a MemberSpecializationInfo pointer
+  /// For function template specializations, this will be a
-  /// containing information about the specialization. For function template
+  /// FunctionTemplateSpecializationInfo, which contains information about
-  /// specializations, this will be a FunctionTemplateSpecializationInfo, which
+  /// the template being specialized and the template arguments involved in
-  /// contains information about the template being specialized and the template
+  /// that specialization.
-  /// arguments involved in that specialization.
+  llvm::PointerUnion<FunctionTemplateDecl *,
-  llvm::PointerUnion<FunctionDecl *, FunctionTemplateDecl *,
                      MemberSpecializationInfo *,
                      FunctionTemplateSpecializationInfo *,
                      DependentFunctionTemplateSpecializationInfo *>
@@ -2691,11 +2688,6 @@ public:
     setInstantiationOfMemberFunction(getASTContext(), FD, TSK);
   }
 
-  /// Specify that this function declaration was instantiated from FunctionDecl
-  /// FD. This is only used if this is a function declaration declared locally
-  /// inside of a function template.
-  void setInstantiatedFromDecl(FunctionDecl *FD);
-
   /// Retrieves the function template that is described by this
   /// function declaration.
   ///
@@ -2710,8 +2702,6 @@ public:
   /// FunctionTemplateDecl from a FunctionDecl.
   FunctionTemplateDecl *getDescribedFunctionTemplate() const;
 
-  FunctionDecl *getInstantiatedFromDecl() const;
-
   void setDescribedFunctionTemplate(FunctionTemplateDecl *Template);
 
   /// Determine whether this function is a function template

clang/include/clang/AST/DeclBase.h

@@ -906,14 +906,6 @@ public:
                     const_cast<const Decl*>(this)->getParentFunctionOrMethod());
   }
 
-  /// Does the same thing as getParentFunctionOrMethod, except starts with the
-  /// lexical declaration context instead.
-  const DeclContext *getLexicalParentFunctionOrMethod() const;
-  DeclContext *getLexicalParentFunctionOrMethod() {
-    return const_cast<DeclContext *>(
-        const_cast<const Decl *>(this)->getLexicalParentFunctionOrMethod());
-  }
-
   /// Retrieves the "canonical" declaration of the given declaration.
   virtual Decl *getCanonicalDecl() { return this; }
   const Decl *getCanonicalDecl() const {

clang/include/clang/Sema/Sema.h

@@ -6989,34 +6989,7 @@ private:
       LocalInstantiationScope &Scope,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
-  /// used by SetupConstraintCheckingTemplateArgumentsAndScope to recursively(in
-  /// the case of lambdas) set up the LocalInstantiationScope of the current
-  /// function.
-  bool SetupConstraintScope(
-      FunctionDecl *FD, llvm::Optional<ArrayRef<TemplateArgument>> TemplateArgs,
-      MultiLevelTemplateArgumentList MLTAL, LocalInstantiationScope &Scope);
-
-  /// Used during constraint checking, sets up the constraint template arguemnt
-  /// lists, and calls SetupConstraintScope to set up the
-  /// LocalInstantiationScope to have the proper set of ParVarDecls configured.
-  llvm::Optional<MultiLevelTemplateArgumentList>
-  SetupConstraintCheckingTemplateArgumentsAndScope(
-      FunctionDecl *FD, llvm::Optional<ArrayRef<TemplateArgument>> TemplateArgs,
-      LocalInstantiationScope &Scope);
-
-  // Keep track of whether we are evaluating a constraint.
-  unsigned ConstraintEvaluationDepth = 0;
-
-  class ConstraintEvalRAII {
-    Sema &S;
-
 public:
-    ConstraintEvalRAII(Sema &S) : S(S) { ++S.ConstraintEvaluationDepth; }
-    ~ConstraintEvalRAII() { --S.ConstraintEvaluationDepth; }
-  };
-
-public:
-  bool IsEvaluatingAConstraint() { return ConstraintEvaluationDepth > 0; }
   const NormalizedConstraint *
   getNormalizedAssociatedConstraints(
       NamedDecl *ConstrainedDecl, ArrayRef<const Expr *> AssociatedConstraints);
@@ -7046,10 +7019,8 @@ public:
   /// check (either a concept or a constrained entity).
   /// \param ConstraintExprs a list of constraint expressions, treated as if
   /// they were 'AND'ed together.
-  /// \param TemplateArgList the multi-level list of template arguments to
+  /// \param TemplateArgs the list of template arguments to substitute into the
-  /// substitute into the constraint expression. This should be relative to the
+  /// constraint expression.
-  /// top-level (hence multi-level), since we need to instantiate fully at the
-  /// time of checking.
   /// \param TemplateIDRange The source range of the template id that
   /// caused the constraints check.
   /// \param Satisfaction if true is returned, will contain details of the
@@ -7059,40 +7030,7 @@ public:
   /// false otherwise.
   bool CheckConstraintSatisfaction(
       const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
-      const MultiLevelTemplateArgumentList &TemplateArgList,
+      ArrayRef<TemplateArgument> TemplateArgs,
-      SourceRange TemplateIDRange, ConstraintSatisfaction &Satisfaction) {
-    llvm::SmallVector<Expr *, 4> Converted;
-    return CheckConstraintSatisfaction(Template, ConstraintExprs, Converted,
-                                       TemplateArgList, TemplateIDRange,
-                                       Satisfaction);
-  }
-
-  /// \brief Check whether the given list of constraint expressions are
-  /// satisfied (as if in a 'conjunction') given template arguments.
-  /// Additionally, takes an empty list of Expressions which is populated with
-  /// the instantiated versions of the ConstraintExprs.
-  /// \param Template the template-like entity that triggered the constraints
-  /// check (either a concept or a constrained entity).
-  /// \param ConstraintExprs a list of constraint expressions, treated as if
-  /// they were 'AND'ed together.
-  /// \param ConvertedConstraints a out parameter that will get populated with
-  /// the instantiated version of the ConstraintExprs if we successfully checked
-  /// satisfaction.
-  /// \param TemplateArgList the multi-level list of template arguments to
-  /// substitute into the constraint expression. This should be relative to the
-  /// top-level (hence multi-level), since we need to instantiate fully at the
-  /// time of checking.
-  /// \param TemplateIDRange The source range of the template id that
-  /// caused the constraints check.
-  /// \param Satisfaction if true is returned, will contain details of the
-  /// satisfaction, with enough information to diagnose an unsatisfied
-  /// expression.
-  /// \returns true if an error occurred and satisfaction could not be checked,
-  /// false otherwise.
-  bool CheckConstraintSatisfaction(
-      const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
-      llvm::SmallVectorImpl<Expr *> &ConvertedConstraints,
-      const MultiLevelTemplateArgumentList &TemplateArgList,
       SourceRange TemplateIDRange, ConstraintSatisfaction &Satisfaction);
 
   /// \brief Check whether the given non-dependent constraint expression is
@@ -7128,8 +7066,8 @@ public:
   ///
   /// \returns true if the constrains are not satisfied or could not be checked
   /// for satisfaction, false if the constraints are satisfied.
-  bool EnsureTemplateArgumentListConstraints(
+  bool EnsureTemplateArgumentListConstraints(TemplateDecl *Template,
-      TemplateDecl *Template, MultiLevelTemplateArgumentList TemplateArgs,
+                                       ArrayRef<TemplateArgument> TemplateArgs,
                                              SourceRange TemplateIDRange);
 
   /// \brief Emit diagnostics explaining why a constraint expression was deemed
@@ -8864,8 +8802,7 @@ public:
 
   MultiLevelTemplateArgumentList getTemplateInstantiationArgs(
       const NamedDecl *D, const TemplateArgumentList *Innermost = nullptr,
-      bool RelativeToPrimary = false, const FunctionDecl *Pattern = nullptr,
+      bool RelativeToPrimary = false, const FunctionDecl *Pattern = nullptr);
-      bool LookBeyondLambda = false, bool IncludeContainingStruct = false);
 
   /// A context in which code is being synthesized (where a source location
   /// alone is not sufficient to identify the context). This covers template
@@ -9586,11 +9523,6 @@ public:
                       ExtParameterInfoBuilder &ParamInfos);
   ExprResult SubstExpr(Expr *E,
                        const MultiLevelTemplateArgumentList &TemplateArgs);
-  // Unlike the above, this evaluates constraints, which should only happen at
-  // 'constraint checking' time.
-  ExprResult
-  SubstConstraintExpr(Expr *E,
-                      const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Substitute the given template arguments into a list of
   /// expressions, expanding pack expansions if required.

clang/include/clang/Sema/Template.h

@@ -75,9 +75,6 @@ enum class TemplateSubstitutionKind : char {
   class MultiLevelTemplateArgumentList {
     /// The template argument list at a certain template depth
     using ArgList = ArrayRef<TemplateArgument>;
-    using ArgListsIterator = SmallVector<ArgList, 4>::reverse_iterator;
-    using ConstArgListsIterator =
-        SmallVector<ArgList, 4>::const_reverse_iterator;
 
     /// The template argument lists, stored from the innermost template
     /// argument list (first) to the outermost template argument list (last).
@@ -124,12 +121,6 @@ enum class TemplateSubstitutionKind : char {
       return TemplateArgumentLists.size();
     }
 
-    /// Determine the number of substituted args at 'Depth'.
-    unsigned getNumSubstitutedArgs(unsigned Depth) const {
-      assert(NumRetainedOuterLevels <= Depth && Depth < getNumLevels());
-      return TemplateArgumentLists[getNumLevels() - Depth - 1].size();
-    }
-
     unsigned getNumRetainedOuterLevels() const {
       return NumRetainedOuterLevels;
     }
@@ -167,14 +158,6 @@ enum class TemplateSubstitutionKind : char {
       return !(*this)(Depth, Index).isNull();
     }
 
-    bool isAnyArgInstantiationDependent() const {
-      for (ArgList List : TemplateArgumentLists)
-        for (const TemplateArgument &TA : List)
-          if (TA.isInstantiationDependent())
-            return true;
-      return false;
-    }
-
     /// Clear out a specific template argument.
     void setArgument(unsigned Depth, unsigned Index,
                      TemplateArgument Arg) {
@@ -214,16 +197,6 @@ enum class TemplateSubstitutionKind : char {
     const ArgList &getInnermost() const {
       return TemplateArgumentLists.front();
     }
-
-    /// Retrieve the outermost template argument list.
-    const ArgList &getOutermost() const { return TemplateArgumentLists.back(); }
-
-    ArgListsIterator begin() { return TemplateArgumentLists.rbegin(); }
-    ConstArgListsIterator begin() const {
-      return TemplateArgumentLists.rbegin();
-    }
-    ArgListsIterator end() { return TemplateArgumentLists.rend(); }
-    ConstArgListsIterator end() const { return TemplateArgumentLists.rend(); }
   };
 
   /// The context in which partial ordering of function templates occurs.

clang/lib/AST/ASTImporter.cpp

@@ -3109,11 +3109,6 @@ Error ASTNodeImporter::ImportTemplateInformation(
   case FunctionDecl::TK_FunctionTemplate:
     return Error::success();
 
-  case FunctionDecl::TK_DependentNonTemplate:
-    if (Expected<FunctionDecl *> InstFDOrErr =
-            import(FromFD->getInstantiatedFromDecl()))
-      ToFD->setInstantiatedFromDecl(*InstFDOrErr);
-    return Error::success();
   case FunctionDecl::TK_MemberSpecialization: {
     TemplateSpecializationKind TSK = FromFD->getTemplateSpecializationKind();
 

clang/lib/AST/Decl.cpp

@@ -3729,8 +3729,6 @@ const IdentifierInfo *FunctionDecl::getLiteralIdentifier() const {
 FunctionDecl::TemplatedKind FunctionDecl::getTemplatedKind() const {
   if (TemplateOrSpecialization.isNull())
     return TK_NonTemplate;
-  if (TemplateOrSpecialization.is<FunctionDecl *>())
-    return TK_DependentNonTemplate;
   if (TemplateOrSpecialization.is<FunctionTemplateDecl *>())
     return TK_FunctionTemplate;
   if (TemplateOrSpecialization.is<MemberSpecializationInfo *>())
@@ -3782,16 +3780,6 @@ void FunctionDecl::setDescribedFunctionTemplate(FunctionTemplateDecl *Template)
   TemplateOrSpecialization = Template;
 }
 
-void FunctionDecl::setInstantiatedFromDecl(FunctionDecl *FD) {
-  assert(TemplateOrSpecialization.isNull() &&
-         "function is already a specialization");
-  TemplateOrSpecialization = FD;
-}
-
-FunctionDecl *FunctionDecl::getInstantiatedFromDecl() const {
-  return TemplateOrSpecialization.dyn_cast<FunctionDecl *>();
-}
-
 bool FunctionDecl::isImplicitlyInstantiable() const {
   // If the function is invalid, it can't be implicitly instantiated.
   if (isInvalidDecl())

clang/lib/AST/DeclBase.cpp

@@ -293,16 +293,6 @@ const DeclContext *Decl::getParentFunctionOrMethod() const {
   return nullptr;
 }
 
-const DeclContext *Decl::getLexicalParentFunctionOrMethod() const {
-  for (const DeclContext *DC = getLexicalDeclContext();
-       DC && !DC->isTranslationUnit() && !DC->isNamespace();
-       DC = DC->getParent())
-    if (DC->isFunctionOrMethod())
-      return DC;
-
-  return nullptr;
-}
-
 //===----------------------------------------------------------------------===//
 // PrettyStackTraceDecl Implementation
 //===----------------------------------------------------------------------===//

clang/lib/ExtractAPI/ExtractAPIConsumer.cpp

@@ -161,7 +161,6 @@ public:
     // Skip templated functions.
     switch (Decl->getTemplatedKind()) {
     case FunctionDecl::TK_NonTemplate:
-    case FunctionDecl::TK_DependentNonTemplate:
       break;
     case FunctionDecl::TK_MemberSpecialization:
     case FunctionDecl::TK_FunctionTemplateSpecialization:

clang/lib/Sema/SemaConcept.cpp

@@ -30,7 +30,6 @@ using namespace sema;
 
 namespace {
 class LogicalBinOp {
-  SourceLocation Loc;
   OverloadedOperatorKind Op = OO_None;
   const Expr *LHS = nullptr;
   const Expr *RHS = nullptr;
@@ -41,14 +40,12 @@ public:
       Op = BinaryOperator::getOverloadedOperator(BO->getOpcode());
       LHS = BO->getLHS();
       RHS = BO->getRHS();
-      Loc = BO->getExprLoc();
     } else if (auto *OO = dyn_cast<CXXOperatorCallExpr>(E)) {
       // If OO is not || or && it might not have exactly 2 arguments.
       if (OO->getNumArgs() == 2) {
         Op = OO->getOperator();
         LHS = OO->getArg(0);
         RHS = OO->getArg(1);
-        Loc = OO->getOperatorLoc();
       }
     }
   }
@@ -59,25 +56,6 @@ public:
 
   const Expr *getLHS() const { return LHS; }
   const Expr *getRHS() const { return RHS; }
-
-  ExprResult recreateBinOp(Sema &SemaRef, ExprResult LHS) {
-    return recreateBinOp(SemaRef, LHS, const_cast<Expr *>(getRHS()));
-  }
-
-  ExprResult recreateBinOp(Sema &SemaRef, ExprResult LHS, ExprResult RHS) {
-    assert((isAnd() || isOr()) && "Not the right kind of op?");
-    assert((!LHS.isInvalid() && !RHS.isInvalid()) && "not good expressions?");
-
-    if (!LHS.isUsable() || !RHS.isUsable())
-      return ExprEmpty();
-
-    // We should just be able to 'normalize' these to the builtin Binary
-    // Operator, since that is how they are evaluated in constriant checks.
-    return BinaryOperator::Create(SemaRef.Context, LHS.get(), RHS.get(),
-                                  BinaryOperator::getOverloadedOpcode(Op),
-                                  SemaRef.Context.BoolTy, VK_PRValue,
-                                  OK_Ordinary, Loc, FPOptionsOverride{});
-  }
 };
 }
 
@@ -144,18 +122,16 @@ bool Sema::CheckConstraintExpression(const Expr *ConstraintExpression,
 }
 
 template <typename AtomicEvaluator>
-static ExprResult
+static bool
 calculateConstraintSatisfaction(Sema &S, const Expr *ConstraintExpr,
                                 ConstraintSatisfaction &Satisfaction,
                                 AtomicEvaluator &&Evaluator) {
   ConstraintExpr = ConstraintExpr->IgnoreParenImpCasts();
 
   if (LogicalBinOp BO = ConstraintExpr) {
-    ExprResult LHSRes = calculateConstraintSatisfaction(
+    if (calculateConstraintSatisfaction(S, BO.getLHS(), Satisfaction,
-        S, BO.getLHS(), Satisfaction, Evaluator);
+                                        Evaluator))
-
+      return true;
-    if (LHSRes.isInvalid())
-      return ExprError();
 
     bool IsLHSSatisfied = Satisfaction.IsSatisfied;
 
@@ -166,7 +142,7 @@ calculateConstraintSatisfaction(Sema &S, const Expr *ConstraintExpr,
       //    is checked. If that is satisfied, the disjunction is satisfied.
       //    Otherwise, the disjunction is satisfied if and only if the second
       //    operand is satisfied.
-      return LHSRes.isUsable() ? BO.recreateBinOp(S, LHSRes) : ExprEmpty();
+      return false;
 
     if (BO.isAnd() && !IsLHSSatisfied)
       // [temp.constr.op] p2
@@ -175,21 +151,12 @@ calculateConstraintSatisfaction(Sema &S, const Expr *ConstraintExpr,
       //    is checked. If that is not satisfied, the conjunction is not
       //    satisfied. Otherwise, the conjunction is satisfied if and only if
       //    the second operand is satisfied.
-      return LHSRes.isUsable() ? BO.recreateBinOp(S, LHSRes) : ExprEmpty();
+      return false;
 
-    ExprResult RHSRes = calculateConstraintSatisfaction(
-        S, BO.getRHS(), Satisfaction, std::forward<AtomicEvaluator>(Evaluator));
-    if (RHSRes.isInvalid())
-      return ExprError();
-
-    if (!LHSRes.isUsable() || !RHSRes.isUsable())
-      return ExprEmpty();
-    return BO.recreateBinOp(S, LHSRes, RHSRes);
-  } else if (auto *C = dyn_cast<ExprWithCleanups>(ConstraintExpr)) {
-    // These aren't evaluated, so we don't care about cleanups, so we can just
-    // evaluate these as if the cleanups didn't exist.
     return calculateConstraintSatisfaction(
-        S, C->getSubExpr(), Satisfaction,
+        S, BO.getRHS(), Satisfaction, std::forward<AtomicEvaluator>(Evaluator));
+  } else if (auto *C = dyn_cast<ExprWithCleanups>(ConstraintExpr)) {
+    return calculateConstraintSatisfaction(S, C->getSubExpr(), Satisfaction,
         std::forward<AtomicEvaluator>(Evaluator));
   }
 
@@ -197,11 +164,11 @@ calculateConstraintSatisfaction(Sema &S, const Expr *ConstraintExpr,
   ExprResult SubstitutedAtomicExpr = Evaluator(ConstraintExpr);
 
   if (SubstitutedAtomicExpr.isInvalid())
-    return ExprError();
+    return true;
 
   if (!SubstitutedAtomicExpr.isUsable())
     // Evaluator has decided satisfaction without yielding an expression.
-    return ExprEmpty();
+    return false;
 
   EnterExpressionEvaluationContext ConstantEvaluated(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
@@ -218,7 +185,7 @@ calculateConstraintSatisfaction(Sema &S, const Expr *ConstraintExpr,
         << SubstitutedAtomicExpr.get()->getSourceRange();
     for (const PartialDiagnosticAt &PDiag : EvaluationDiags)
       S.Diag(PDiag.first, PDiag.second);
-    return ExprError();
+    return true;
   }
 
   assert(EvalResult.Val.isInt() &&
@@ -228,13 +195,13 @@ calculateConstraintSatisfaction(Sema &S, const Expr *ConstraintExpr,
     Satisfaction.Details.emplace_back(ConstraintExpr,
                                       SubstitutedAtomicExpr.get());
 
-  return SubstitutedAtomicExpr;
+  return false;
 }
 
-static ExprResult calculateConstraintSatisfaction(
+static bool calculateConstraintSatisfaction(
-    Sema &S, const NamedDecl *Template, SourceLocation TemplateNameLoc,
+    Sema &S, const NamedDecl *Template, ArrayRef<TemplateArgument> TemplateArgs,
-    const MultiLevelTemplateArgumentList &MLTAL, const Expr *ConstraintExpr,
+    SourceLocation TemplateNameLoc, MultiLevelTemplateArgumentList &MLTAL,
-    ConstraintSatisfaction &Satisfaction) {
+    const Expr *ConstraintExpr, ConstraintSatisfaction &Satisfaction) {
   return calculateConstraintSatisfaction(
       S, ConstraintExpr, Satisfaction, [&](const Expr *AtomicExpr) {
         EnterExpressionEvaluationContext ConstantEvaluated(
@@ -252,8 +219,8 @@ static ExprResult calculateConstraintSatisfaction(
             return ExprError();
           // We do not want error diagnostics escaping here.
           Sema::SFINAETrap Trap(S);
-          SubstitutedExpression =
+          SubstitutedExpression = S.SubstExpr(const_cast<Expr *>(AtomicExpr),
-              S.SubstConstraintExpr(const_cast<Expr *>(AtomicExpr), MLTAL);
+                                              MLTAL);
           // Substitution might have stripped off a contextual conversion to
           // bool if this is the operand of an '&&' or '||'. For example, we
           // might lose an lvalue-to-rvalue conversion here. If so, put it back
@@ -301,92 +268,74 @@ static ExprResult calculateConstraintSatisfaction(
       });
 }
 
-static bool CheckConstraintSatisfaction(
+static bool CheckConstraintSatisfaction(Sema &S, const NamedDecl *Template,
-    Sema &S, const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
+                                        ArrayRef<const Expr *> ConstraintExprs,
-    llvm::SmallVectorImpl<Expr *> &Converted,
+                                        ArrayRef<TemplateArgument> TemplateArgs,
-    const MultiLevelTemplateArgumentList &TemplateArgsList,
+                                        SourceRange TemplateIDRange,
-    SourceRange TemplateIDRange, ConstraintSatisfaction &Satisfaction) {
+                                        ConstraintSatisfaction &Satisfaction) {
   if (ConstraintExprs.empty()) {
     Satisfaction.IsSatisfied = true;
     return false;
   }
 
-  if (TemplateArgsList.isAnyArgInstantiationDependent()) {
+  for (auto& Arg : TemplateArgs)
+    if (Arg.isInstantiationDependent()) {
       // No need to check satisfaction for dependent constraint expressions.
       Satisfaction.IsSatisfied = true;
       return false;
     }
 
-  ArrayRef<TemplateArgument> TemplateArgs =
+  Sema::InstantiatingTemplate Inst(S, TemplateIDRange.getBegin(),
-      TemplateArgsList.getNumSubstitutedLevels() > 0
-          ? TemplateArgsList.getOutermost()
-          : ArrayRef<TemplateArgument>{};
-
-  Sema::InstantiatingTemplate Inst(
-      S, TemplateIDRange.getBegin(),
       Sema::InstantiatingTemplate::ConstraintsCheck{},
       const_cast<NamedDecl *>(Template), TemplateArgs, TemplateIDRange);
   if (Inst.isInvalid())
     return true;
 
-  for (const Expr *ConstraintExpr : ConstraintExprs) {
+  MultiLevelTemplateArgumentList MLTAL;
-    ExprResult Res = calculateConstraintSatisfaction(
+  MLTAL.addOuterTemplateArguments(TemplateArgs);
-        S, Template, TemplateIDRange.getBegin(), TemplateArgsList,
-        ConstraintExpr, Satisfaction);
-    if (Res.isInvalid())
-      return true;
 
-    Converted.push_back(Res.get());
+  for (const Expr *ConstraintExpr : ConstraintExprs) {
-    if (!Satisfaction.IsSatisfied) {
+    if (calculateConstraintSatisfaction(S, Template, TemplateArgs,
-      // Backfill the 'converted' list with nulls so we can keep the Converted
+                                        TemplateIDRange.getBegin(), MLTAL,
-      // and unconverted lists in sync.
+                                        ConstraintExpr, Satisfaction))
-      Converted.append(ConstraintExprs.size() - Converted.size(), nullptr);
+      return true;
+    if (!Satisfaction.IsSatisfied)
       // [temp.constr.op] p2
       //   [...] To determine if a conjunction is satisfied, the satisfaction
       //   of the first operand is checked. If that is not satisfied, the
       //   conjunction is not satisfied. [...]
       return false;
   }
-  }
   return false;
 }
 
 bool Sema::CheckConstraintSatisfaction(
     const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
-    llvm::SmallVectorImpl<Expr *> &ConvertedConstraints,
+    ArrayRef<TemplateArgument> TemplateArgs, SourceRange TemplateIDRange,
-    const MultiLevelTemplateArgumentList &TemplateArgsList,
+    ConstraintSatisfaction &OutSatisfaction) {
-    SourceRange TemplateIDRange, ConstraintSatisfaction &OutSatisfaction) {
   if (ConstraintExprs.empty()) {
     OutSatisfaction.IsSatisfied = true;
     return false;
   }
 
-  // A list of the template argument list flattened in a predictible manner for
-  // the purposes of caching. The ConstraintSatisfaction type is in AST so it
-  // has no access to the MultiLevelTemplateArgumentList, so this has to happen
-  // here.
-  llvm::SmallVector<TemplateArgument, 4> FlattenedArgs;
-  for (ArrayRef<TemplateArgument> List : TemplateArgsList)
-    FlattenedArgs.insert(FlattenedArgs.end(), List.begin(), List.end());
-
   llvm::FoldingSetNodeID ID;
   void *InsertPos;
   ConstraintSatisfaction *Satisfaction = nullptr;
   bool ShouldCache = LangOpts.ConceptSatisfactionCaching && Template;
   if (ShouldCache) {
-    ConstraintSatisfaction::Profile(ID, Context, Template, FlattenedArgs);
+    ConstraintSatisfaction::Profile(ID, Context, Template, TemplateArgs);
     Satisfaction = SatisfactionCache.FindNodeOrInsertPos(ID, InsertPos);
     if (Satisfaction) {
       OutSatisfaction = *Satisfaction;
       return false;
     }
-    Satisfaction = new ConstraintSatisfaction(Template, FlattenedArgs);
+    Satisfaction = new ConstraintSatisfaction(Template, TemplateArgs);
   } else {
     Satisfaction = &OutSatisfaction;
   }
   if (::CheckConstraintSatisfaction(*this, Template, ConstraintExprs,
-                                    ConvertedConstraints, TemplateArgsList,
+                                    TemplateArgs, TemplateIDRange,
-                                    TemplateIDRange, *Satisfaction)) {
+                                    *Satisfaction)) {
     if (ShouldCache)
       delete Satisfaction;
     return true;
@@ -407,108 +356,17 @@ bool Sema::CheckConstraintSatisfaction(const Expr *ConstraintExpr,
       *this, ConstraintExpr, Satisfaction,
       [](const Expr *AtomicExpr) -> ExprResult {
         return ExprResult(const_cast<Expr *>(AtomicExpr));
-             })
+      });
-      .isInvalid();
-}
-
-bool Sema::SetupConstraintScope(
-    FunctionDecl *FD, llvm::Optional<ArrayRef<TemplateArgument>> TemplateArgs,
-    MultiLevelTemplateArgumentList MLTAL, LocalInstantiationScope &Scope) {
-  if (FD->isTemplateInstantiation() && FD->getPrimaryTemplate()) {
-    FunctionTemplateDecl *PrimaryTemplate = FD->getPrimaryTemplate();
-    InstantiatingTemplate Inst(
-        *this, FD->getPointOfInstantiation(),
-        Sema::InstantiatingTemplate::ConstraintsCheck{}, PrimaryTemplate,
-        TemplateArgs ? *TemplateArgs : ArrayRef<TemplateArgument>{},
-        SourceRange());
-    if (Inst.isInvalid())
-      return true;
-
-    // addInstantiatedParametersToScope creates a map of 'uninstantiated' to
-    // 'instantiated' parameters and adds it to the context. For the case where
-    // this function is a template being instantiated NOW, we also need to add
-    // the list of current template arguments to the list so that they also can
-    // be picked out of the map.
-    if (auto *SpecArgs = FD->getTemplateSpecializationArgs()) {
-      MultiLevelTemplateArgumentList JustTemplArgs(*SpecArgs);
-      if (addInstantiatedParametersToScope(
-              FD, PrimaryTemplate->getTemplatedDecl(), Scope, JustTemplArgs))
-        return true;
-    }
-
-    // If this is a member function, make sure we get the parameters that
-    // reference the original primary template.
-    if (const auto *FromMemTempl =
-            PrimaryTemplate->getInstantiatedFromMemberTemplate()) {
-      if (addInstantiatedParametersToScope(FD, FromMemTempl->getTemplatedDecl(),
-                                           Scope, MLTAL))
-        return true;
-    }
-  } else if (FD->getTemplatedKind() == FunctionDecl::TK_MemberSpecialization ||
-             FD->getTemplatedKind() == FunctionDecl::TK_DependentNonTemplate) {
-    FunctionDecl *InstantiatedFrom =
-        FD->getTemplatedKind() == FunctionDecl::TK_MemberSpecialization
-            ? FD->getInstantiatedFromMemberFunction()
-            : FD->getInstantiatedFromDecl();
-
-    InstantiatingTemplate Inst(
-        *this, FD->getPointOfInstantiation(),
-        Sema::InstantiatingTemplate::ConstraintsCheck{}, InstantiatedFrom,
-        TemplateArgs ? *TemplateArgs : ArrayRef<TemplateArgument>{},
-        SourceRange());
-    if (Inst.isInvalid())
-      return true;
-
-    // Case where this was not a template, but instantiated as a child-function.
-    if (addInstantiatedParametersToScope(FD, InstantiatedFrom, Scope, MLTAL))
-      return true;
-  }
-
-  return false;
-}
-
-// This function collects all of the template arguments for the purposes of
-// constraint-instantiation and checking.
-llvm::Optional<MultiLevelTemplateArgumentList>
-Sema::SetupConstraintCheckingTemplateArgumentsAndScope(
-    FunctionDecl *FD, llvm::Optional<ArrayRef<TemplateArgument>> TemplateArgs,
-    LocalInstantiationScope &Scope) {
-  MultiLevelTemplateArgumentList MLTAL;
-
-  // Collect the list of template arguments relative to the 'primary' template.
-  // We need the entire list, since the constraint is completely uninstantiated
-  // at this point.
-  MLTAL = getTemplateInstantiationArgs(FD, nullptr, /*RelativeToPrimary*/ true,
-                                       /*Pattern*/ nullptr,
-                                       /*LookBeyondLambda*/ true);
-  if (SetupConstraintScope(FD, TemplateArgs, MLTAL, Scope))
-    return {};
-
-  return MLTAL;
 }
 
 bool Sema::CheckFunctionConstraints(const FunctionDecl *FD,
                                     ConstraintSatisfaction &Satisfaction,
                                     SourceLocation UsageLoc) {
-  // Don't check constraints if the function is dependent. Also don't check if
+  const Expr *RC = FD->getTrailingRequiresClause();
-  // this is a function template specialization, as the call to
+  if (RC->isInstantiationDependent()) {
-  // CheckinstantiatedFunctionTemplateConstraints after this will check it
-  // better.
-  if (FD->isDependentContext() ||
-      FD->getTemplatedKind() ==
-          FunctionDecl::TK_FunctionTemplateSpecialization) {
     Satisfaction.IsSatisfied = true;
     return false;
   }
-
-  ContextRAII SavedContext{
-      *this, cast<DeclContext>(
-                 const_cast<FunctionDecl *>(FD)->getNonClosureContext())};
-  LocalInstantiationScope Scope(*this, true);
-  llvm::Optional<MultiLevelTemplateArgumentList> MLTAL =
-      SetupConstraintCheckingTemplateArgumentsAndScope(
-          const_cast<FunctionDecl *>(FD), {}, Scope);
-
   Qualifiers ThisQuals;
   CXXRecordDecl *Record = nullptr;
   if (auto *Method = dyn_cast<CXXMethodDecl>(FD)) {
@@ -519,27 +377,14 @@ bool Sema::CheckFunctionConstraints(const FunctionDecl *FD,
   // We substitute with empty arguments in order to rebuild the atomic
   // constraint in a constant-evaluated context.
   // FIXME: Should this be a dedicated TreeTransform?
-  const Expr *RC = FD->getTrailingRequiresClause();
+  return CheckConstraintSatisfaction(
-  llvm::SmallVector<Expr *, 1> Converted;
+      FD, {RC}, /*TemplateArgs=*/{},
-
-  if (CheckConstraintSatisfaction(
-          FD, {RC}, Converted, *MLTAL,
       SourceRange(UsageLoc.isValid() ? UsageLoc : FD->getLocation()),
-          Satisfaction))
+      Satisfaction);
-    return true;
-
-  // FIXME: we need to do this for the function constraints for
-  // comparison of constraints to work, but do we also need to do it for
-  // CheckInstantiatedFunctionConstraints?  That one is more difficult, but we
-  // seem to always just pick up the constraints from the primary template.
-  assert(Converted.size() <= 1 && "Got more expressions converted?");
-  if (!Converted.empty() && Converted[0] != nullptr)
-    const_cast<FunctionDecl *>(FD)->setTrailingRequiresClause(Converted[0]);
-  return false;
 }
 
 bool Sema::EnsureTemplateArgumentListConstraints(
-    TemplateDecl *TD, MultiLevelTemplateArgumentList TemplateArgs,
+    TemplateDecl *TD, ArrayRef<TemplateArgument> TemplateArgs,
     SourceRange TemplateIDRange) {
   ConstraintSatisfaction Satisfaction;
   llvm::SmallVector<const Expr *, 3> AssociatedConstraints;
@@ -552,8 +397,7 @@ bool Sema::EnsureTemplateArgumentListConstraints(
     SmallString<128> TemplateArgString;
     TemplateArgString = " ";
     TemplateArgString += getTemplateArgumentBindingsText(
-        TD->getTemplateParameters(), TemplateArgs.getInnermost().data(),
+        TD->getTemplateParameters(), TemplateArgs.data(), TemplateArgs.size());
-        TemplateArgs.getInnermost().size());
 
     Diag(TemplateIDRange.getBegin(),
          diag::err_template_arg_list_constraints_not_satisfied)
@@ -585,13 +429,21 @@ bool Sema::CheckInstantiatedFunctionTemplateConstraints(
   Sema::ContextRAII savedContext(*this, Decl);
   LocalInstantiationScope Scope(*this);
 
-  Optional<MultiLevelTemplateArgumentList> MLTAL =
+  // If this is not an explicit specialization - we need to get the instantiated
-      SetupConstraintCheckingTemplateArgumentsAndScope(Decl, TemplateArgs,
+  // version of the template arguments and add them to scope for the
-                                                       Scope);
+  // substitution.
-
+  if (Decl->isTemplateInstantiation()) {
-  if (!MLTAL)
+    InstantiatingTemplate Inst(*this, Decl->getPointOfInstantiation(),
+        InstantiatingTemplate::ConstraintsCheck{}, Decl->getPrimaryTemplate(),
+        TemplateArgs, SourceRange());
+    if (Inst.isInvalid())
       return true;
-
+    MultiLevelTemplateArgumentList MLTAL(
+        *Decl->getTemplateSpecializationArgs());
+    if (addInstantiatedParametersToScope(
+            Decl, Decl->getPrimaryTemplate()->getTemplatedDecl(), Scope, MLTAL))
+      return true;
+  }
   Qualifiers ThisQuals;
   CXXRecordDecl *Record = nullptr;
   if (auto *Method = dyn_cast<CXXMethodDecl>(Decl)) {
@@ -599,8 +451,7 @@ bool Sema::CheckInstantiatedFunctionTemplateConstraints(
     Record = Method->getParent();
   }
   CXXThisScopeRAII ThisScope(*this, Record, ThisQuals, Record != nullptr);
-  llvm::SmallVector<Expr *, 1> Converted;
+  return CheckConstraintSatisfaction(Template, TemplateAC, TemplateArgs,
-  return CheckConstraintSatisfaction(Template, TemplateAC, Converted, *MLTAL,
                                      PointOfInstantiation, Satisfaction);
 }
 

clang/lib/Sema/SemaTemplate.cpp

@@ -4702,11 +4702,9 @@ Sema::CheckConceptTemplateId(const CXXScopeSpec &SS,
   bool AreArgsDependent =
       TemplateSpecializationType::anyDependentTemplateArguments(*TemplateArgs,
                                                                 Converted);
-  MultiLevelTemplateArgumentList MLTAL;
-  MLTAL.addOuterTemplateArguments(Converted);
   if (!AreArgsDependent &&
       CheckConstraintSatisfaction(
-          NamedConcept, {NamedConcept->getConstraintExpr()}, MLTAL,
+          NamedConcept, {NamedConcept->getConstraintExpr()}, Converted,
           SourceRange(SS.isSet() ? SS.getBeginLoc() : ConceptNameInfo.getLoc(),
                       TemplateArgs->getRAngleLoc()),
           Satisfaction))
@@ -5566,7 +5564,6 @@ bool Sema::CheckTemplateArgument(NamedDecl *Param,
     if (Inst.isInvalid())
       return true;
 
-    ConstraintEvalRAII EvalRAII(*this);
     TemplateArgumentList TemplateArgs(TemplateArgumentList::OnStack, Converted);
     Params = SubstTemplateParams(Params, CurContext,
                                  MultiLevelTemplateArgumentList(TemplateArgs));
@@ -5924,21 +5921,14 @@ bool Sema::CheckTemplateArgumentList(
   if (UpdateArgsWithConversions)
     TemplateArgs = std::move(NewArgs);
 
-  if (!PartialTemplateArgs) {
+  if (!PartialTemplateArgs &&
-    TemplateArgumentList StackTemplateArgs(TemplateArgumentList::OnStack,
+      EnsureTemplateArgumentListConstraints(
-                                           Converted);
+        Template, Converted, SourceRange(TemplateLoc,
-    MultiLevelTemplateArgumentList MLTAL = getTemplateInstantiationArgs(
+                                         TemplateArgs.getRAngleLoc()))) {
-        Template, &StackTemplateArgs, /*RelativeToPrimary*/ true,
-        /*Pattern*/ nullptr,
-        /*LookBeyondLambda*/ true, /*IncludeContainingStruct*/ true);
-    if (EnsureTemplateArgumentListConstraints(
-            Template, MLTAL,
-            SourceRange(TemplateLoc, TemplateArgs.getRAngleLoc()))) {
     if (ConstraintsNotSatisfied)
       *ConstraintsNotSatisfied = true;
     return true;
   }
-  }
 
   return false;
 }
@@ -7467,9 +7457,7 @@ bool Sema::CheckTemplateTemplateArgument(TemplateTemplateParmDecl *Param,
       //   are not considered.
       if (ParamsAC.empty())
         return false;
-
       Template->getAssociatedConstraints(TemplateAC);
-
       bool IsParamAtLeastAsConstrained;
       if (IsAtLeastAsConstrained(Param, ParamsAC, Template, TemplateAC,
                                  IsParamAtLeastAsConstrained))

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -2791,10 +2791,8 @@ CheckDeducedArgumentConstraints(Sema& S, TemplateDeclT *Template,
                                 TemplateDeductionInfo& Info) {
   llvm::SmallVector<const Expr *, 3> AssociatedConstraints;
   Template->getAssociatedConstraints(AssociatedConstraints);
-  MultiLevelTemplateArgumentList MLTAL;
+  if (S.CheckConstraintSatisfaction(Template, AssociatedConstraints,
-  MLTAL.addOuterTemplateArguments(DeducedArgs);
+                                    DeducedArgs, Info.getLocation(),
-  if (S.CheckConstraintSatisfaction(Template, AssociatedConstraints, MLTAL,
-                                    Info.getLocation(),
                                     Info.AssociatedConstraintsSatisfaction) ||
       !Info.AssociatedConstraintsSatisfaction.IsSatisfied) {
     Info.reset(TemplateArgumentList::CreateCopy(S.Context, DeducedArgs));
@@ -4574,11 +4572,8 @@ CheckDeducedPlaceholderConstraints(Sema &S, const AutoType &Type,
   if (S.CheckTemplateArgumentList(Concept, SourceLocation(), TemplateArgs,
                                   /*PartialTemplateArgs=*/false, Converted))
     return Sema::DAR_FailedAlreadyDiagnosed;
-
-  MultiLevelTemplateArgumentList MLTAL;
-  MLTAL.addOuterTemplateArguments(Converted);
   if (S.CheckConstraintSatisfaction(Concept, {Concept->getConstraintExpr()},
-                                    MLTAL, TypeLoc.getLocalSourceRange(),
+                                    Converted, TypeLoc.getLocalSourceRange(),
                                     Satisfaction))
     return Sema::DAR_FailedAlreadyDiagnosed;
   if (!Satisfaction.IsSatisfied) {

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -55,18 +55,9 @@ using namespace sema;
 /// instantiating the definition of the given declaration, \p D. This is
 /// used to determine the proper set of template instantiation arguments for
 /// friend function template specializations.
-///
-/// \param LookBeyondLambda Indicates that this collection of arguments should
-/// continue looking when it encounters a lambda generic call operator.
-///
-/// \param IncludeContainingStructArgs Indicates that this collection of
-/// arguments should include arguments for any class template that this
-/// declaration is included inside of.
-
 MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
     const NamedDecl *D, const TemplateArgumentList *Innermost,
-    bool RelativeToPrimary, const FunctionDecl *Pattern, bool LookBeyondLambda,
+    bool RelativeToPrimary, const FunctionDecl *Pattern) {
-    bool IncludeContainingStructArgs) {
   // Accumulate the set of template argument lists in this structure.
   MultiLevelTemplateArgumentList Result;
 
@@ -162,13 +153,11 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
           break;
 
         // If this function is a generic lambda specialization, we are done.
-        if (!LookBeyondLambda &&
+        if (isGenericLambdaCallOperatorOrStaticInvokerSpecialization(Function))
-            isGenericLambdaCallOperatorOrStaticInvokerSpecialization(Function))
           break;
 
       } else if (Function->getDescribedFunctionTemplate()) {
-        assert((IncludeContainingStructArgs ||
+        assert(Result.getNumSubstitutedLevels() == 0 &&
-                Result.getNumSubstitutedLevels() == 0) &&
                "Outer template not instantiated?");
       }
 
@@ -185,18 +174,10 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
       }
     } else if (const auto *Rec = dyn_cast<CXXRecordDecl>(Ctx)) {
       if (ClassTemplateDecl *ClassTemplate = Rec->getDescribedClassTemplate()) {
-        assert((IncludeContainingStructArgs ||
+        assert(Result.getNumSubstitutedLevels() == 0 &&
-                Result.getNumSubstitutedLevels() == 0) &&
                "Outer template not instantiated?");
         if (ClassTemplate->isMemberSpecialization())
           break;
-        if (IncludeContainingStructArgs) {
-          QualType RecordType = Context.getTypeDeclType(Rec);
-          QualType Injected = cast<InjectedClassNameType>(RecordType)
-                                  ->getInjectedSpecializationType();
-          const auto *InjectedType = cast<TemplateSpecializationType>(Injected);
-          Result.addOuterTemplateArguments(InjectedType->template_arguments());
-        }
       }
     }
 
@@ -2323,18 +2304,6 @@ bool Sema::SubstTypeConstraint(
     const MultiLevelTemplateArgumentList &TemplateArgs) {
   const ASTTemplateArgumentListInfo *TemplArgInfo =
       TC->getTemplateArgsAsWritten();
-
-  // If we're not checking a constraint, we shouldn't be instantiating the type
-  // constraint, so we should just create a copy of the previous one.
-  // TODO: ERICH: Should this be RebuildExprInCurrentInstantiation here?
-  if (!IsEvaluatingAConstraint()) {
-    Inst->setTypeConstraint(TC->getNestedNameSpecifierLoc(),
-                            TC->getConceptNameInfo(), TC->getNamedConcept(),
-                            TC->getNamedConcept(), TemplArgInfo,
-                            TC->getImmediatelyDeclaredConstraint());
-    return false;
-  }
-
   TemplateArgumentListInfo InstArgs;
 
   if (TemplArgInfo) {
@@ -3519,14 +3488,6 @@ Sema::SubstExpr(Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs) {
   return Instantiator.TransformExpr(E);
 }
 
-ExprResult
-Sema::SubstConstraintExpr(Expr *E,
-                          const MultiLevelTemplateArgumentList &TemplateArgs) {
-
-  ConstraintEvalRAII EvalRAII(*this);
-  return SubstExpr(E, TemplateArgs);
-}
-
 ExprResult Sema::SubstInitializer(Expr *Init,
                           const MultiLevelTemplateArgumentList &TemplateArgs,
                           bool CXXDirectInit) {

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -2062,7 +2062,19 @@ Decl *TemplateDeclInstantiator::VisitFunctionDecl(
       return nullptr;
   }
 
+  // FIXME: Concepts: Do not substitute into constraint expressions
   Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
+  if (TrailingRequiresClause) {
+    EnterExpressionEvaluationContext ConstantEvaluated(
+        SemaRef, Sema::ExpressionEvaluationContext::Unevaluated);
+    ExprResult SubstRC = SemaRef.SubstExpr(TrailingRequiresClause,
+                                           TemplateArgs);
+    if (SubstRC.isInvalid())
+      return nullptr;
+    TrailingRequiresClause = SubstRC.get();
+    if (!SemaRef.CheckConstraintExpression(TrailingRequiresClause))
+      return nullptr;
+  }
 
   // If we're instantiating a local function declaration, put the result
   // in the enclosing namespace; otherwise we need to find the instantiated
@@ -2170,11 +2182,6 @@ Decl *TemplateDeclInstantiator::VisitFunctionDecl(
     // definition. We don't want non-template functions to be marked as being
     // template instantiations.
     Function->setInstantiationOfMemberFunction(D, TSK_ImplicitInstantiation);
-  } else if (!isFriend) {
-    // If this is not a function template, and this is not a friend (that is,
-    // this is a locally declared function), save the instantiation relationship
-    // for the purposes of constraint instantiation.
-    Function->setInstantiatedFromDecl(D);
   }
 
   if (isFriend) {
@@ -2413,6 +2420,23 @@ Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(
       return nullptr;
   }
 
+  // FIXME: Concepts: Do not substitute into constraint expressions
+  Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
+  if (TrailingRequiresClause) {
+    EnterExpressionEvaluationContext ConstantEvaluated(
+        SemaRef, Sema::ExpressionEvaluationContext::Unevaluated);
+    auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(Owner);
+    Sema::CXXThisScopeRAII ThisScope(SemaRef, ThisContext,
+                                     D->getMethodQualifiers(), ThisContext);
+    ExprResult SubstRC = SemaRef.SubstExpr(TrailingRequiresClause,
+                                           TemplateArgs);
+    if (SubstRC.isInvalid())
+      return nullptr;
+    TrailingRequiresClause = SubstRC.get();
+    if (!SemaRef.CheckConstraintExpression(TrailingRequiresClause))
+      return nullptr;
+  }
+
   DeclContext *DC = Owner;
   if (isFriend) {
     if (QualifierLoc) {
@@ -2430,9 +2454,6 @@ Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(
     if (!DC) return nullptr;
   }
 
-  CXXRecordDecl *Record = cast<CXXRecordDecl>(DC);
-  Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
-
   DeclarationNameInfo NameInfo
     = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);
 
@@ -2440,6 +2461,7 @@ Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(
     adjustForRewrite(FunctionRewriteKind, D, T, TInfo, NameInfo);
 
   // Build the instantiated method declaration.
+  CXXRecordDecl *Record = cast<CXXRecordDecl>(DC);
   CXXMethodDecl *Method = nullptr;
 
   SourceLocation StartLoc = D->getInnerLocStart();
@@ -2746,6 +2768,9 @@ Decl *TemplateDeclInstantiator::VisitTemplateTypeParmDecl(
       // Invented template parameter type constraints will be instantiated with
       // the corresponding auto-typed parameter as it might reference other
       // parameters.
+
+      // TODO: Concepts: do not instantiate the constraint (delayed constraint
+      // substitution)
       if (SemaRef.SubstTypeConstraint(Inst, TC, TemplateArgs))
         return nullptr;
     }
@@ -3988,7 +4013,18 @@ TemplateDeclInstantiator::SubstTemplateParams(TemplateParameterList *L) {
   if (Invalid)
     return nullptr;
 
-  Expr *InstRequiresClause = L->getRequiresClause();
+  // FIXME: Concepts: Substitution into requires clause should only happen when
+  // checking satisfaction.
+  Expr *InstRequiresClause = nullptr;
+  if (Expr *E = L->getRequiresClause()) {
+    EnterExpressionEvaluationContext ConstantEvaluated(
+        SemaRef, Sema::ExpressionEvaluationContext::Unevaluated);
+    ExprResult Res = SemaRef.SubstExpr(E, TemplateArgs);
+    if (Res.isInvalid() || !Res.isUsable()) {
+      return nullptr;
+    }
+    InstRequiresClause = Res.get();
+  }
 
   TemplateParameterList *InstL
     = TemplateParameterList::Create(SemaRef.Context, L->getTemplateLoc(),

clang/lib/Sema/TreeTransform.h

@@ -12997,6 +12997,13 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
                                                         NewCallOpType);
   }
 
+  // Transform the trailing requires clause
+  ExprResult NewTrailingRequiresClause;
+  if (Expr *TRC = E->getCallOperator()->getTrailingRequiresClause())
+    // FIXME: Concepts: Substitution into requires clause should only happen
+    //                  when checking satisfaction.
+    NewTrailingRequiresClause = getDerived().TransformExpr(TRC);
+
   // Create the local class that will describe the lambda.
 
   // FIXME: DependencyKind below is wrong when substituting inside a templated
@@ -13031,7 +13038,7 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
       E->getCallOperator()->getEndLoc(),
       NewCallOpTSI->getTypeLoc().castAs<FunctionProtoTypeLoc>().getParams(),
       E->getCallOperator()->getConstexprKind(),
-      E->getCallOperator()->getTrailingRequiresClause());
+      NewTrailingRequiresClause.get());
 
   LSI->CallOperator = NewCallOperator;
 

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -941,10 +941,6 @@ void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
   case FunctionDecl::TK_NonTemplate:
     mergeRedeclarable(FD, Redecl);
     break;
-  case FunctionDecl::TK_DependentNonTemplate:
-    mergeRedeclarable(FD, Redecl);
-    FD->setInstantiatedFromDecl(readDeclAs<FunctionDecl>());
-    break;
   case FunctionDecl::TK_FunctionTemplate:
     // Merged when we merge the template.
     FD->setDescribedFunctionTemplate(readDeclAs<FunctionTemplateDecl>());

clang/lib/Serialization/ASTWriterDecl.cpp

@@ -585,9 +585,6 @@ void ASTDeclWriter::VisitFunctionDecl(FunctionDecl *D) {
   switch (D->getTemplatedKind()) {
   case FunctionDecl::TK_NonTemplate:
     break;
-  case FunctionDecl::TK_DependentNonTemplate:
-    Record.AddDeclRef(D->getInstantiatedFromDecl());
-    break;
   case FunctionDecl::TK_FunctionTemplate:
     Record.AddDeclRef(D->getDescribedFunctionTemplate());
     break;

clang/test/CXX/temp/temp.constr/temp.constr.constr/non-function-templates.cpp

@@ -90,24 +90,3 @@ struct D { };
 
 static_assert(C<int>{}); // expected-note{{while checking constraint satisfaction for template 'C<int>' required here}}
 static_assert(D<int>{}); // expected-note{{while checking constraint satisfaction for template 'D<int>' required here}}
-
-// Test the delayed instantiation, the 'foo' implementation shouldn't cause the
-// constraint failure(or crash!) until the use to create 'y'.
-namespace DelayedInst {
-template <unsigned I>
-struct AAA {
-  template <typename T>
-    requires(sizeof(T) == I) // expected-note {{because 'sizeof(int) == 5U' (4 == 5) evaluated to false}}
-  struct B {
-    static constexpr int a = 0;
-  };
-
-  static constexpr auto foo() {
-    return B<int>::a; // expected-error{{constraints not satisfied for class template 'B' [with T = int]}}
-  }
-};
-
-constexpr auto x = AAA<4>::foo();
-constexpr auto y = AAA<5>::foo(); // expected-note {{in instantiation of member function 'DelayedInst::AAA<5>::foo' requested here}}
-
-} // namespace DelayedInst

clang/test/SemaTemplate/concepts.cpp

@@ -256,249 +256,3 @@ C auto **j1 = g();   // expected-error {{deduced type 'int' does not satisfy 'C'
 C auto **&j2 = g();  // expected-error {{deduced type 'int' does not satisfy 'C'}}
 C auto **&&j3 = g(); // expected-error {{deduced type 'int' does not satisfy 'C'}}
 }
-
-namespace DeferredInstantiationInstScope {
-template <typename T>
-struct remove_ref {
-  using type = T;
-};
-template <typename T>
-struct remove_ref<T &> {
-  using type = T;
-};
-template <typename T>
-struct remove_ref<T &&> {
-  using type = T;
-};
-
-template <typename T>
-constexpr bool IsInt = PR54443::is_same<typename remove_ref<T>::type,
-                                        int>::value;
-
-template <typename U>
-void SingleDepthReferencesTop(U &&u) {
-  struct lc {
-    void operator()()             // #SDRT_OP
-      requires IsInt<decltype(u)> // #SDRT_REQ
-    {}
-  };
-  lc lv;
-  lv(); // #SDRT_CALL
-}
-
-template <typename U>
-void SingleDepthReferencesTopNotCalled(U &&u) {
-  struct lc {
-    void operator()()
-      requires IsInt<typename decltype(u)::FOO>
-    {}
-  };
-  lc lv;
-}
-
-template <typename U>
-void SingleDepthReferencesTopCalled(U &&u) {
-  struct lc {
-    void operator()()                           // #CALLOP
-      requires IsInt<typename decltype(u)::FOO> // #CONSTR
-    {}
-  };
-  lc lv;
-  lv();
-  // expected-error@-1{{no matching function for call to object of type 'lc'}}
-  // expected-note@#SDRTC{{in instantiation of function template}}
-  // expected-note@#CALLOP{{constraints not satisfied}}
-  // expected-note@#CONSTR{{substituted constraint expression is ill-formed}}
-}
-
-template <typename U>
-void SingleDepthReferencesTopLambda(U &&u) {
-  []()
-    requires IsInt<decltype(u)>
-  {}();
-}
-
-template <typename U>
-void DoubleDepthReferencesTop(U &&u) {
-  struct lc { // #DDRT_STRCT
-    void operator()() {
-      struct lc2 {
-        void operator()()             // #DDRT_OP
-          requires IsInt<decltype(u)> // #DDRT_REQ
-        {}
-      };
-      lc2 lv2;
-      lv2(); // #DDRT_CALL
-    }
-  };
-  lc lv;
-  lv();
-}
-
-template <typename U>
-void DoubleDepthReferencesTopLambda(U &&u) {
-  []() { []()
-           requires IsInt<decltype(u)>
-         {}(); }();
-}
-
-template <typename U>
-void DoubleDepthReferencesAll(U &&u) {
-  struct lc { // #DDRA_STRCT
-    void operator()(U &&u2) {
-      struct lc2 {
-        void operator()(U &&u3)          // #DDRA_OP
-          requires IsInt<decltype(u)> && // #DDRA_REQ
-                   IsInt<decltype(u2)> && IsInt<decltype(u3)>
-        {}
-      };
-      lc2 lv2;
-      lv2(u2); // #DDRA_CALL
-    }
-  };
-  lc lv;
-  lv(u);
-}
-
-template <typename U>
-void DoubleDepthReferencesAllLambda(U &&u) {
-  [](U &&u2) {
-    [](U && u3)
-      requires IsInt<decltype(u)> &&
-               IsInt<decltype(u2)> && IsInt<decltype(u3)>
-    {}(u2);
-  }(u);
-}
-
-template <typename U>
-void HasInnerFunc(U &&u) {
-  void InnerFunc(U && u2)
-    requires IsInt<decltype(u)> && // #INNERFUNC_REQ
-             IsInt<decltype(u2)>;
-  InnerFunc(u); // #INNERFUNC_CALL
-}
-
-template <typename U>
-struct CausesFriendConstraint {
-  template <typename V>
-  friend void FriendFunc(CausesFriendConstraint, V) // #FF_DECL
-    requires IsInt<U> &&
-             IsInt<V> // #FF_REQ
-  {}
-};
-// FIXME: Re-enable this test when constraints are allowed to refer to captures.
-// template<typename T>
-// void ChecksCapture(T x) {
-//   [y = x]() requires(IsInt<decltype(y)>){}();
-// }
-
-template <typename T>
-void ChecksLocalVar(T x) {
-  T Local;
-  []()
-    requires(IsInt<decltype(Local)>)
-  {}();
-}
-
-template <typename T>
-void LocalStructMemberVar(T x) {
-  struct S {
-    T local;
-    void foo()
-      requires(IsInt<decltype(local)>) // #LSMV_REQ
-    {}
-  } s;
-  s.foo(); // #LSMV_CALL
-};
-
-template <typename T>
-struct ChecksMemberVar {
-  T t;
-  void foo()
-    requires(IsInt<decltype(t)>) // #CMV_FOO
-  {}
-  template <typename U>
-  void foo2()                    // #CMV_FOO2
-    requires(IsInt<decltype(t)>) // #CMV_FOO2_REQ
-  {}
-};
-
-void test_dependent() {
-  int v = 0;
-  float will_fail;
-  SingleDepthReferencesTop(v);
-  SingleDepthReferencesTop(will_fail);
-  // expected-error@#SDRT_CALL{{no matching function for call to object of type 'lc'}}
-  // expected-note@-2{{in instantiation of function template specialization}}
-  // expected-note@#SDRT_OP{{candidate function not viable}}
-  // expected-note@#SDRT_REQ{{'IsInt<decltype(u)>' evaluated to false}}
-
-  SingleDepthReferencesTopNotCalled(v);
-  // Won't error unless we try to call it.
-  SingleDepthReferencesTopNotCalled(will_fail);
-  SingleDepthReferencesTopCalled(v); // #SDRTC
-  SingleDepthReferencesTopLambda(v);
-  // FIXME: This should error on constraint failure! (Lambda!)
-  SingleDepthReferencesTopLambda(will_fail);
-  DoubleDepthReferencesTop(v);
-  DoubleDepthReferencesTop(will_fail);
-  // expected-error@#DDRT_CALL{{no matching function for call to object of type 'lc2'}}
-  // expected-note@-2{{in instantiation of function template specialization}}
-  // expected-note@#DDRT_STRCT{{in instantiation of member function}}
-  // expected-note@#DDRT_OP{{candidate function not viable}}
-  // expected-note@#DDRT_REQ{{'IsInt<decltype(u)>' evaluated to false}}
-
-  DoubleDepthReferencesTopLambda(v);
-  // FIXME: This should error on constraint failure! (Lambda!)
-  DoubleDepthReferencesTopLambda(will_fail);
-  DoubleDepthReferencesAll(v);
-  DoubleDepthReferencesAll(will_fail);
-  // expected-error@#DDRA_CALL{{no matching function for call to object of type 'lc2'}}
-  // expected-note@-2{{in instantiation of function template specialization}}
-  // expected-note@#DDRA_STRCT{{in instantiation of member function}}
-  // expected-note@#DDRA_OP{{candidate function not viable}}
-  // expected-note@#DDRA_REQ{{'IsInt<decltype(u)>' evaluated to false}}
-
-  DoubleDepthReferencesAllLambda(v);
-  // FIXME: This should error on constraint failure! (Lambda!)
-  DoubleDepthReferencesAllLambda(will_fail);
-  HasInnerFunc(v);
-  HasInnerFunc(will_fail);
-  // expected-error@#INNERFUNC_CALL{{invalid reference to function 'InnerFunc': constraints not satisfied}}
-  // expected-note@-2{{in instantiation of function template specialization}}
-  // expected-note@#INNERFUNC_REQ{{'IsInt<decltype(u)>' evaluated to false}}
-
-  CausesFriendConstraint<int> CFC;
-  FriendFunc(CFC, 1);
-  FriendFunc(CFC, 1.0);
-  // expected-error@-1{{no matching function for call to 'FriendFunc'}}
-  // expected-note@#FF_DECL{{constraints not satisfied}}
-  // expected-note@#FF_REQ{{because 'IsInt<double>' evaluated to false}}
-
-  // FIXME: Re-enable this test when constraints are allowed to refer to captures.
-  // ChecksCapture(v);
-
-  ChecksLocalVar(v);
-  // FIXME: This should error on constraint failure! (Lambda!)
-  ChecksLocalVar(will_fail);
-
-  LocalStructMemberVar(v);
-  LocalStructMemberVar(will_fail);
-  // expected-error@#LSMV_CALL{{invalid reference to function 'foo'}}
-  // expected-note@-2{{in instantiation of function template specialization}}
-  // expected-note@#LSMV_REQ{{because 'IsInt<decltype(this->local)>' evaluated to false}}
-
-  ChecksMemberVar<int> CMV;
-  CMV.foo();
-  CMV.foo2<int>();
-
-  ChecksMemberVar<float> CMV2;
-  CMV2.foo();
-  // expected-error@-1{{invalid reference to function 'foo'}}
-  // expected-note@#CMV_FOO{{because 'IsInt<decltype(this->t)>' evaluated to false}}
-  CMV2.foo2<float>();
-  // expected-error@-1{{no matching member function for call to 'foo2'}}
-  // expected-note@#CMV_FOO2{{constraints not satisfied}}
-  // expected-note@#CMV_FOO2_REQ{{because 'IsInt<decltype(this->t)>' evaluated to false}}
-}
-} // namespace DeferredInstantiationInstScope

clang/test/SemaTemplate/deferred-concept-inst.cpp

@@ -1,23 +0,0 @@
-// RUN: %clang_cc1 -std=c++2a -x c++ %s -verify -Wno-unused-value
-// expected-no-diagnostics
-
-namespace GithubBug44178 {
-template <typename D>
-struct CRTP {
-  void call_foo()
-    requires requires(D &v) { v.foo(); }
-  {
-    static_cast<D *>(this)->foo();
-  }
-};
-
-struct Test : public CRTP<Test> {
-  void foo() {}
-};
-
-int main() {
-  Test t;
-  t.call_foo();
-  return 0;
-}
-} // namespace GithubBug44178

clang/test/SemaTemplate/instantiate-requires-clause.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++2a -x c++ %s -Wno-unused-value -verify
+// RUN: %clang_cc1 -std=c++2a -x c++ %s -verify
 
 template <typename... Args> requires ((sizeof(Args) == 1), ...)
 // expected-note@-1 {{because '(sizeof(int) == 1) , (sizeof(char) == 1) , (sizeof(int) == 1)' evaluated to false}}
@@ -40,20 +40,6 @@ struct S {
 
 static_assert(S<void>::f(1));
 
-// Similar to the 'S' test, but tries to use 'U' in the requires clause.
-template <typename T2>
-struct S1 {
-  // expected-note@+3 {{candidate template ignored: constraints not satisfied [with U = int]}}
-  // expected-note@+3 {{because substituted constraint expression is ill-formed: type 'int' cannot be used prior to '::' because it has no members}}
-  template <typename U>
-  static constexpr auto f(U const index)
-    requires(U::foo)
-  { return true; }
-};
-
-// expected-error@+1 {{no matching function for call to 'f'}}
-static_assert(S1<void>::f(1));
-
 constexpr auto value = 0;
 
 template<typename T>

clang/test/SemaTemplate/trailing-return-short-circuit.cpp

@@ -1,62 +0,0 @@
-// RUN: %clang_cc1 -std=c++20 -verify %s
-
-template <class T>
-  requires(sizeof(T) > 2) || T::value // #FOO_REQ
-void Foo(T){};                        // #FOO
-
-template <class T>
-void TrailingReturn(T)       // #TRAILING
-  requires(sizeof(T) > 2) || // #TRAILING_REQ
-          T::value           // #TRAILING_REQ_VAL
-{};
-template <bool B>
-struct HasValue {
-  static constexpr bool value = B;
-};
-static_assert(sizeof(HasValue<true>) <= 2);
-
-template <bool B>
-struct HasValueLarge {
-  static constexpr bool value = B;
-  int I;
-};
-static_assert(sizeof(HasValueLarge<true>) > 2);
-
-void usage() {
-  // Passes the 1st check, short-circuit so the 2nd ::value is not evaluated.
-  Foo(1.0);
-  TrailingReturn(1.0);
-
-  // Fails the 1st check, but has a ::value, so the check happens correctly.
-  Foo(HasValue<true>{});
-  TrailingReturn(HasValue<true>{});
-
-  // Passes the 1st check, but would have passed the 2nd one.
-  Foo(HasValueLarge<true>{});
-  TrailingReturn(HasValueLarge<true>{});
-
-  // Fails the 1st check, fails 2nd because there is no ::value.
-  Foo(true);
-  // expected-error@-1{{no matching function for call to 'Foo'}}
-  // expected-note@#FOO{{candidate template ignored: constraints not satisfied [with T = bool]}}
-  // expected-note@#FOO_REQ{{because 'sizeof(_Bool) > 2' (1 > 2) evaluated to false}}
-  // expected-note@#FOO_REQ{{because substituted constraint expression is ill-formed: type 'bool' cannot be used prior to '::' because it has no members}}
-
-  TrailingReturn(true);
-  // expected-error@-1{{no matching function for call to 'TrailingReturn'}}
-  // expected-note@#TRAILING{{candidate template ignored: constraints not satisfied [with T = bool]}}
-  // expected-note@#TRAILING_REQ{{because 'sizeof(_Bool) > 2' (1 > 2) evaluated to false}}
-  // expected-note@#TRAILING_REQ_VAL{{because substituted constraint expression is ill-formed: type 'bool' cannot be used prior to '::' because it has no members}}
-
-  // Fails the 1st check, fails 2nd because ::value is false.
-  Foo(HasValue<false>{});
-  // expected-error@-1 {{no matching function for call to 'Foo'}}
-  // expected-note@#FOO{{candidate template ignored: constraints not satisfied [with T = HasValue<false>]}}
-  // expected-note@#FOO_REQ{{because 'sizeof(HasValue<false>) > 2' (1 > 2) evaluated to false}}
-  // expected-note@#FOO_REQ{{and 'HasValue<false>::value' evaluated to false}}
-  TrailingReturn(HasValue<false>{});
-  // expected-error@-1 {{no matching function for call to 'TrailingReturn'}}
-  // expected-note@#TRAILING{{candidate template ignored: constraints not satisfied [with T = HasValue<false>]}}
-  // expected-note@#TRAILING_REQ{{because 'sizeof(HasValue<false>) > 2' (1 > 2) evaluated to false}}
-  // expected-note@#TRAILING_REQ_VAL{{and 'HasValue<false>::value' evaluated to false}}
-}