Use virtual functions in ParsedAttrInfo instead of function pointers

This doesn't do anything on its own, but it's the first step towards
allowing plugins to define attributes. It does simplify the
ParsedAttrInfo generation in ClangAttrEmitter a little though.

Differential Revision: https://reviews.llvm.org/D31337

Author: john-brawn-arm

clang/lib/Sema/ParsedAttr.cpp

@@ -110,13 +110,26 @@ struct ParsedAttrInfo {
   unsigned IsKnownToGCC : 1;
   unsigned IsSupportedByPragmaAttribute : 1;
 
-  bool (*DiagAppertainsToDecl)(Sema &S, const ParsedAttr &Attr, const Decl *);
-  bool (*DiagLangOpts)(Sema &S, const ParsedAttr &Attr);
-  bool (*ExistsInTarget)(const TargetInfo &Target);
-  unsigned (*SpellingIndexToSemanticSpelling)(const ParsedAttr &Attr);
-  void (*GetPragmaAttributeMatchRules)(
-      llvm::SmallVectorImpl<std::pair<attr::SubjectMatchRule, bool>> &Rules,
-      const LangOptions &LangOpts);
+  virtual ~ParsedAttrInfo() = default;
+
+  virtual bool diagAppertainsToDecl(Sema &S, const ParsedAttr &Attr,
+                                    const Decl *) const {
+    return true;
+  }
+  virtual bool diagLangOpts(Sema &S, const ParsedAttr &Attr) const {
+    return true;
+  }
+  virtual bool existsInTarget(const TargetInfo &Target) const {
+    return true;
+  }
+  virtual unsigned
+  spellingIndexToSemanticSpelling(const ParsedAttr &Attr) const {
+    return UINT_MAX;
+  }
+  virtual void getPragmaAttributeMatchRules(
+    llvm::SmallVectorImpl<std::pair<attr::SubjectMatchRule, bool>> &Rules,
+    const LangOptions &LangOpts) const {
+  }
 };
 
 namespace {
@@ -126,7 +139,13 @@ namespace {
 } // namespace
 
 static const ParsedAttrInfo &getInfo(const ParsedAttr &A) {
-  return AttrInfoMap[A.getKind()];
+  // If we have a ParsedAttrInfo for this ParsedAttr then return that,
+  // otherwise return a default ParsedAttrInfo.
+  if (A.getKind() < llvm::array_lengthof(AttrInfoMap))
+    return *AttrInfoMap[A.getKind()];
+
+  static ParsedAttrInfo DefaultParsedAttrInfo;
+  return DefaultParsedAttrInfo;
 }
 
 unsigned ParsedAttr::getMinArgs() const { return getInfo(*this).NumArgs; }
@@ -140,7 +159,7 @@ bool ParsedAttr::hasCustomParsing() const {
 }
 
 bool ParsedAttr::diagnoseAppertainsTo(Sema &S, const Decl *D) const {
-  return getInfo(*this).DiagAppertainsToDecl(S, *this, D);
+  return getInfo(*this).diagAppertainsToDecl(S, *this, D);
 }
 
 bool ParsedAttr::appliesToDecl(const Decl *D,
@@ -152,11 +171,11 @@ void ParsedAttr::getMatchRules(
     const LangOptions &LangOpts,
     SmallVectorImpl<std::pair<attr::SubjectMatchRule, bool>> &MatchRules)
     const {
-  return getInfo(*this).GetPragmaAttributeMatchRules(MatchRules, LangOpts);
+  return getInfo(*this).getPragmaAttributeMatchRules(MatchRules, LangOpts);
 }
 
 bool ParsedAttr::diagnoseLangOpts(Sema &S) const {
-  return getInfo(*this).DiagLangOpts(S, *this);
+  return getInfo(*this).diagLangOpts(S, *this);
 }
 
 bool ParsedAttr::isTargetSpecificAttr() const {
@@ -168,7 +187,7 @@ bool ParsedAttr::isTypeAttr() const { return getInfo(*this).IsType; }
 bool ParsedAttr::isStmtAttr() const { return getInfo(*this).IsStmt; }
 
 bool ParsedAttr::existsInTarget(const TargetInfo &Target) const {
-  return getInfo(*this).ExistsInTarget(Target);
+  return getInfo(*this).existsInTarget(Target);
 }
 
 bool ParsedAttr::isKnownToGCC() const { return getInfo(*this).IsKnownToGCC; }
@@ -178,7 +197,7 @@ bool ParsedAttr::isSupportedByPragmaAttribute() const {
 }
 
 unsigned ParsedAttr::getSemanticSpelling() const {
-  return getInfo(*this).SpellingIndexToSemanticSpelling(*this);
+  return getInfo(*this).spellingIndexToSemanticSpelling(*this);
 }
 
 bool ParsedAttr::hasVariadicArg() const {