Revert "[Concepts] Placeholder constraints and abbreviated templates"

This reverts commit e57a9ab.

Parser/cxx2a-placeholder-type-constraint.cpp has MSan failures.

Present at 7b81c3f:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap-msan/builds/17133/steps/check-clang%20msan/logs/stdio
not present at eaa594f:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap-msan/builds/17132/steps/check-clang%20msan/logs/stdio

Stack trace:
```
==57032==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0xccfe016 in clang::AutoTypeLoc::getLocalSourceRange() const /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/include/clang/AST/TypeLoc.h:2036:19
    #1 0xcc56758 in CheckDeducedPlaceholderConstraints(clang::Sema&, clang::AutoType const&, clang::AutoTypeLoc, clang::QualType) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Sema/SemaTemplateDeduction.cpp:4505:56
    #2 0xcc550ce in clang::Sema::DeduceAutoType(clang::TypeLoc, clang::Expr*&, clang::QualType&, llvm::Optional<unsigned int>, bool) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Sema/SemaTemplateDeduction.cpp:4707:11
    #3 0xcc52407 in clang::Sema::DeduceAutoType(clang::TypeSourceInfo*, clang::Expr*&, clang::QualType&, llvm::Optional<unsigned int>, bool) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Sema/SemaTemplateDeduction.cpp:4457:10
    #4 0xba38332 in clang::Sema::deduceVarTypeFromInitializer(clang::VarDecl*, clang::DeclarationName, clang::QualType, clang::TypeSourceInfo*, clang::SourceRange, bool, clang::Expr*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Sema/SemaDecl.cpp:11351:7
    #5 0xba3a8a9 in clang::Sema::DeduceVariableDeclarationType(clang::VarDecl*, bool, clang::Expr*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Sema/SemaDecl.cpp:11385:26
    #6 0xba3c520 in clang::Sema::AddInitializerToDecl(clang::Decl*, clang::Expr*, bool) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Sema/SemaDecl.cpp:11725:9
    #7 0xb39c498 in clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/ParseDecl.cpp:2399:17
    #8 0xb394d80 in clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::SourceLocation*, clang::Parser::ForRangeInit*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/ParseDecl.cpp:2128:21
    #9 0xb383bbf in clang::Parser::ParseSimpleDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::Parser::ParsedAttributesWithRange&, bool, clang::Parser::ForRangeInit*, clang::SourceLocation*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/ParseDecl.cpp:1848:10
    #10 0xb383129 in clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::Parser::ParsedAttributesWithRange&, clang::SourceLocation*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/llvm/include/llvm/ADT/PointerUnion.h
    #11 0xb53a388 in clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::Parser::ParsedAttributesWithRange&) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/ParseStmt.cpp:221:13
    #12 0xb539309 in clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/ParseStmt.cpp:106:20
    #13 0xb55610e in clang::Parser::ParseCompoundStatementBody(bool) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/ParseStmt.cpp:1079:11
    #14 0xb559529 in clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/ParseStmt.cpp:2204:21
    #15 0xb33c13e in clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/Parser.cpp:1339:10
    #16 0xb394703 in clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::SourceLocation*, clang::Parser::ForRangeInit*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/ParseDecl.cpp:2068:11
    #17 0xb338e52 in clang::Parser::ParseDeclOrFunctionDefInternal(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec&, clang::AccessSpecifier) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/Parser.cpp:1099:10
    #18 0xb337674 in clang::Parser::ParseDeclarationOrFunctionDefinition(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*, clang::AccessSpecifier) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/Parser.cpp:1115:12
    #19 0xb334a96 in clang::Parser::ParseExternalDeclaration(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/Parser.cpp:935:12
    #20 0xb32f12a in clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, bool) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/Parser.cpp:686:12
    #21 0xb31e193 in clang::ParseAST(clang::Sema&, bool, bool) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Parse/ParseAST.cpp:158:20
    #22 0x80263f0 in clang::FrontendAction::Execute() /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Frontend/FrontendAction.cpp:936:8
    #23 0x7f2a257 in clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/Frontend/CompilerInstance.cpp:965:33
    #24 0x8288bef in clang::ExecuteCompilerInvocation(clang::CompilerInstance*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp:290:25
    #25 0xad44c2 in cc1_main(llvm::ArrayRef<char const*>, char const*, void*) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/tools/driver/cc1_main.cpp:239:15
    #26 0xacd76a in ExecuteCC1Tool(llvm::ArrayRef<char const*>) /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/tools/driver/driver.cpp:325:12
    #27 0xacc9fd in main /b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm-project/clang/tools/driver/driver.cpp:398:12
    #28 0x7f7d82cdb2e0 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x202e0)
    #29 0xa4dde9 in _start (/b/sanitizer-x86_64-linux-bootstrap-msan/build/llvm_build_msan/bin/clang-11+0xa4dde9)
```

clang/include/clang/AST/ASTContext.h

@@ -88,7 +88,6 @@ class AtomicExpr;
 class BlockExpr;
 class BuiltinTemplateDecl;
 class CharUnits;
-class ConceptDecl;
 class CXXABI;
 class CXXConstructorDecl;
 class CXXMethodDecl;
@@ -212,7 +211,7 @@ class ASTContext : public RefCountedBase<ASTContext> {
   mutable llvm::FoldingSet<ObjCObjectPointerType> ObjCObjectPointerTypes;
   mutable llvm::FoldingSet<DependentUnaryTransformType>
     DependentUnaryTransformTypes;
-  mutable llvm::ContextualFoldingSet<AutoType, ASTContext&> AutoTypes;
+  mutable llvm::FoldingSet<AutoType> AutoTypes;
   mutable llvm::FoldingSet<DeducedTemplateSpecializationType>
     DeducedTemplateSpecializationTypes;
   mutable llvm::FoldingSet<AtomicType> AtomicTypes;
@@ -1543,9 +1542,7 @@ class ASTContext : public RefCountedBase<ASTContext> {
 
   /// C++11 deduced auto type.
   QualType getAutoType(QualType DeducedType, AutoTypeKeyword Keyword,
-                       bool IsDependent, bool IsPack = false,
-                       ConceptDecl *TypeConstraintConcept = nullptr,
-                       ArrayRef<TemplateArgument> TypeConstraintArgs ={}) const;
+                       bool IsDependent, bool IsPack = false) const;
 
   /// C++11 deduction pattern for 'auto' type.
   QualType getAutoDeductType() const;

clang/include/clang/AST/ASTNodeTraverser.h

@@ -548,8 +548,8 @@ class ASTNodeTraverser
   }
 
   void VisitNonTypeTemplateParmDecl(const NonTypeTemplateParmDecl *D) {
-    if (const auto *E = D->getPlaceholderTypeConstraint())
-      Visit(E);
+    if (const auto *TC = D->getPlaceholderTypeConstraint())
+      Visit(TC->getImmediatelyDeclaredConstraint());
     if (D->hasDefaultArgument())
       Visit(D->getDefaultArgument(), SourceRange(),
             D->getDefaultArgStorage().getInheritedFrom(),

clang/include/clang/AST/DeclTemplate.h

@@ -1102,17 +1102,6 @@ class FunctionTemplateDecl : public RedeclarableTemplateDecl {
   /// template.
   ArrayRef<TemplateArgument> getInjectedTemplateArgs();
 
-  /// Return whether this function template is an abbreviated function template,
-  /// e.g. `void foo(auto x)` or `template<typename T> void foo(auto x)`
-  bool isAbbreviated() const {
-    // Since the invented template parameters generated from 'auto' parameters
-    // are either appended to the end of the explicit template parameter list or
-    // form a new template paramter list, we can simply observe the last
-    // parameter to determine if such a thing happened.
-    const TemplateParameterList *TPL = getTemplateParameters();
-    return TPL->getParam(TPL->size() - 1)->isImplicit();
-  }
-
   /// Merge \p Prev with our RedeclarableTemplateDecl::Common.
   void mergePrevDecl(FunctionTemplateDecl *Prev);
 
@@ -1226,6 +1215,7 @@ class TemplateTypeParmDecl final : public TypeDecl,
                                       bool ParameterPack,
                                       bool HasTypeConstraint = false,
                                       Optional<unsigned> NumExpanded = None);
+
   static TemplateTypeParmDecl *CreateDeserialized(const ASTContext &C,
                                                   unsigned ID);
   static TemplateTypeParmDecl *CreateDeserialized(const ASTContext &C,
@@ -1384,8 +1374,7 @@ class NonTypeTemplateParmDecl final
     : public DeclaratorDecl,
       protected TemplateParmPosition,
       private llvm::TrailingObjects<NonTypeTemplateParmDecl,
-                                    std::pair<QualType, TypeSourceInfo *>,
-                                    Expr *> {
+                                    std::pair<QualType, TypeSourceInfo *>> {
   friend class ASTDeclReader;
   friend TrailingObjects;
 
@@ -1440,12 +1429,10 @@ class NonTypeTemplateParmDecl final
          ArrayRef<TypeSourceInfo *> ExpandedTInfos);
 
   static NonTypeTemplateParmDecl *CreateDeserialized(ASTContext &C,
-                                                     unsigned ID,
-                                                     bool HasTypeConstraint);
+                                                     unsigned ID);
   static NonTypeTemplateParmDecl *CreateDeserialized(ASTContext &C,
                                                      unsigned ID,
-                                                     unsigned NumExpandedTypes,
-                                                     bool HasTypeConstraint);
+                                                     unsigned NumExpandedTypes);
 
   using TemplateParmPosition::getDepth;
   using TemplateParmPosition::setDepth;
@@ -1556,22 +1543,20 @@ class NonTypeTemplateParmDecl final
     return TypesAndInfos[I].second;
   }
 
-  /// Return the constraint introduced by the placeholder type of this non-type
+  /// Return the type-constraint in the placeholder type of this non-type
   /// template parameter (if any).
-  Expr *getPlaceholderTypeConstraint() const {
-    return hasPlaceholderTypeConstraint() ? *getTrailingObjects<Expr *>() :
-        nullptr;
-  }
-
-  void setPlaceholderTypeConstraint(Expr *E) {
-    *getTrailingObjects<Expr *>() = E;
+  TypeConstraint *getPlaceholderTypeConstraint() const {
+    // TODO: Concepts: Implement once we have actual placeholders with type
+    //                 constraints.
+    return nullptr;
   }
 
   /// Determine whether this non-type template parameter's type has a
   /// placeholder with a type-constraint.
   bool hasPlaceholderTypeConstraint() const {
-    auto *AT = getType()->getContainedAutoType();
-    return AT && AT->isConstrained();
+    // TODO: Concepts: Implement once we have actual placeholders with type
+    //                 constraints.
+    return false;
   }
 
   /// \brief Get the associated-constraints of this template parameter.
@@ -1581,8 +1566,8 @@ class NonTypeTemplateParmDecl final
   /// Use this instead of getPlaceholderImmediatelyDeclaredConstraint for
   /// concepts APIs that accept an ArrayRef of constraint expressions.
   void getAssociatedConstraints(llvm::SmallVectorImpl<const Expr *> &AC) const {
-    if (Expr *E = getPlaceholderTypeConstraint())
-      AC.push_back(E);
+    if (TypeConstraint *TC = getPlaceholderTypeConstraint())
+      AC.push_back(TC->getImmediatelyDeclaredConstraint());
   }
 
   // Implement isa/cast/dyncast/etc.

clang/include/clang/AST/PropertiesBase.td

@@ -99,8 +99,6 @@ def DeclRef : RefPropertyType<"Decl"> { let ConstWhenWriting = 1; }
     SubclassPropertyType<"TagDecl", DeclRef>;
   def TemplateDeclRef :
     SubclassPropertyType<"TemplateDecl", DeclRef>;
-  def ConceptDeclRef :
-    SubclassPropertyType<"ConceptDecl", DeclRef>;
   def TemplateTypeParmDeclRef :
     SubclassPropertyType<"TemplateTypeParmDecl", DeclRef>;
   def TemplateTemplateParmDeclRef :

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -1040,13 +1040,7 @@ DEF_TRAVERSE_TYPE(UnaryTransformType, {
   TRY_TO(TraverseType(T->getUnderlyingType()));
 })
 
-DEF_TRAVERSE_TYPE(AutoType, {
-  TRY_TO(TraverseType(T->getDeducedType()));
-  if (T->isConstrained()) {
-    TRY_TO(TraverseDecl(T->getTypeConstraintConcept()));
-    TRY_TO(TraverseTemplateArguments(T->getArgs(), T->getNumArgs()));
-  }
-})
+DEF_TRAVERSE_TYPE(AutoType, { TRY_TO(TraverseType(T->getDeducedType())); })
 DEF_TRAVERSE_TYPE(DeducedTemplateSpecializationType, {
   TRY_TO(TraverseTemplateName(T->getTemplateName()));
   TRY_TO(TraverseType(T->getDeducedType()));
@@ -1293,12 +1287,6 @@ DEF_TRAVERSE_TYPELOC(UnaryTransformType, {
 
 DEF_TRAVERSE_TYPELOC(AutoType, {
   TRY_TO(TraverseType(TL.getTypePtr()->getDeducedType()));
-  if (TL.isConstrained()) {
-    TRY_TO(TraverseNestedNameSpecifierLoc(TL.getNestedNameSpecifierLoc()));
-    TRY_TO(TraverseDeclarationNameInfo(TL.getConceptNameInfo()));
-    for (unsigned I = 0, E = TL.getNumArgs(); I != E; ++I)
-      TRY_TO(TraverseTemplateArgumentLoc(TL.getArgLoc(I)));
-  }
 })
 
 DEF_TRAVERSE_TYPELOC(DeducedTemplateSpecializationType, {

clang/include/clang/AST/TemplateBase.h

@@ -637,7 +637,7 @@ struct ASTTemplateArgumentListInfo final
   }
 
   static const ASTTemplateArgumentListInfo *
-  Create(const ASTContext &C, const TemplateArgumentListInfo &List);
+  Create(ASTContext &C, const TemplateArgumentListInfo &List);
 };
 
 /// Represents an explicit template argument list in C++, e.g.,
@@ -702,11 +702,6 @@ inline const TemplateArgument &
   return getArgs()[Idx];
 }
 
-inline const TemplateArgument &AutoType::getArg(unsigned Idx) const {
-  assert(Idx < getNumArgs() && "Template argument out of range");
-  return getArgs()[Idx];
-}
-
 } // namespace clang
 
 #endif // LLVM_CLANG_AST_TEMPLATEBASE_H

clang/include/clang/AST/Type.h

@@ -58,7 +58,6 @@ namespace clang {
 
 class ExtQuals;
 class QualType;
-class ConceptDecl;
 class TagDecl;
 class Type;
 
@@ -1684,15 +1683,6 @@ class alignas(8) Type : public ExtQualsTypeCommonBase {
     /// Was this placeholder type spelled as 'auto', 'decltype(auto)',
     /// or '__auto_type'?  AutoTypeKeyword value.
     unsigned Keyword : 2;
-
-    /// The number of template arguments in the type-constraints, which is
-    /// expected to be able to hold at least 1024 according to [implimits].
-    /// However as this limit is somewhat easy to hit with template
-    /// metaprogramming we'd prefer to keep it as large as possible.
-    /// At the moment it has been left as a non-bitfield since this type
-    /// safely fits in 64 bits as an unsigned, so there is no reason to
-    /// introduce the performance impact of a bitfield.
-    unsigned NumArgs;
   };
 
   class SubstTemplateTypeParmPackTypeBitfields {
@@ -4824,7 +4814,8 @@ class SubstTemplateTypeParmPackType : public Type, public llvm::FoldingSetNode {
 
 /// Common base class for placeholders for types that get replaced by
 /// placeholder type deduction: C++11 auto, C++14 decltype(auto), C++17 deduced
-/// class template types, and constrained type names.
+/// class template types, and (eventually) constrained type names from the C++
+/// Concepts TS.
 ///
 /// These types are usually a placeholder for a deduced type. However, before
 /// the initializer is attached, or (usually) if the initializer is
@@ -4869,50 +4860,18 @@ class DeducedType : public Type {
   }
 };
 
-/// Represents a C++11 auto or C++14 decltype(auto) type, possibly constrained
-/// by a type-constraint.
-class alignas(8) AutoType : public DeducedType, public llvm::FoldingSetNode {
+/// Represents a C++11 auto or C++14 decltype(auto) type.
+class AutoType : public DeducedType, public llvm::FoldingSetNode {
   friend class ASTContext; // ASTContext creates these
 
-  ConceptDecl *TypeConstraintConcept;
-
   AutoType(QualType DeducedAsType, AutoTypeKeyword Keyword,
-           bool IsDeducedAsDependent, bool IsDeducedAsPack, ConceptDecl *CD,
-           ArrayRef<TemplateArgument> TypeConstraintArgs);
-
-  const TemplateArgument *getArgBuffer() const {
-    return reinterpret_cast<const TemplateArgument*>(this+1);
-  }
-
-  TemplateArgument *getArgBuffer() {
-    return reinterpret_cast<TemplateArgument*>(this+1);
+           bool IsDeducedAsDependent, bool IsDeducedAsPack)
+      : DeducedType(Auto, DeducedAsType, IsDeducedAsDependent,
+                    IsDeducedAsDependent, IsDeducedAsPack) {
+    AutoTypeBits.Keyword = (unsigned)Keyword;
   }
 
 public:
-  /// Retrieve the template arguments.
-  const TemplateArgument *getArgs() const {
-    return getArgBuffer();
-  }
-
-  /// Retrieve the number of template arguments.
-  unsigned getNumArgs() const {
-    return AutoTypeBits.NumArgs;
-  }
-
-  const TemplateArgument &getArg(unsigned Idx) const; // in TemplateBase.h
-
-  ArrayRef<TemplateArgument> getTypeConstraintArguments() const {
-    return {getArgs(), getNumArgs()};
-  }
-
-  ConceptDecl *getTypeConstraintConcept() const {
-    return TypeConstraintConcept;
-  }
-
-  bool isConstrained() const {
-    return TypeConstraintConcept != nullptr;
-  }
-
   bool isDecltypeAuto() const {
     return getKeyword() == AutoTypeKeyword::DecltypeAuto;
   }
@@ -4921,15 +4880,18 @@ class alignas(8) AutoType : public DeducedType, public llvm::FoldingSetNode {
     return (AutoTypeKeyword)AutoTypeBits.Keyword;
   }
 
-  void Profile(llvm::FoldingSetNodeID &ID, const ASTContext &Context) {
-    Profile(ID, Context, getDeducedType(), getKeyword(), isDependentType(),
-            getTypeConstraintConcept(), getTypeConstraintArguments());
+  void Profile(llvm::FoldingSetNodeID &ID) {
+    Profile(ID, getDeducedType(), getKeyword(), isDependentType(),
+            containsUnexpandedParameterPack());
   }
 
-  static void Profile(llvm::FoldingSetNodeID &ID, const ASTContext &Context,
-                      QualType Deduced, AutoTypeKeyword Keyword,
-                      bool IsDependent, ConceptDecl *CD,
-                      ArrayRef<TemplateArgument> Arguments);
+  static void Profile(llvm::FoldingSetNodeID &ID, QualType Deduced,
+                      AutoTypeKeyword Keyword, bool IsDependent, bool IsPack) {
+    ID.AddPointer(Deduced.getAsOpaquePtr());
+    ID.AddInteger((unsigned)Keyword);
+    ID.AddBoolean(IsDependent);
+    ID.AddBoolean(IsPack);
+  }
 
   static bool classof(const Type *T) {
     return T->getTypeClass() == Auto;