[Sema][NFCI] Don't allocate storage for the various CorrectionCandidateCallback unless we are going to do some typo correction

The various CorrectionCandidateCallbacks are currently heap-allocated
unconditionally. This was needed because of delayed typo correction.
However these allocations represent currently 15.4% of all allocations
(number of allocations) when parsing all of Boost (!), mostly because
of ParseCastExpression, ParseStatementOrDeclarationAfterAttrtibutes
and isCXXDeclarationSpecifier. Note that all of these callback objects
are small. Let's not do this.

Instead initially allocate the callback on the stack, and only do a
heap allocation if we are going to do some typo correction. Do this by:

1. Adding a clone function to each callback, which will do a polymorphic
   clone of the callback. This clone function is required to be implemented
   by every callback (of which there is a fair amount). Make sure this is
   the case by making it pure virtual.

2. Use this clone function when we are going to try to correct a typo.

This additionally cut the time of -fsyntax-only on all of Boost by 0.5%
(not that much, but still something). No functional changes intended.

Differential Revision: https://reviews.llvm.org/D58827

Reviewed By: rnk

llvm-svn: 356925

1 files changed, 11 insertions, 8 deletions

diff --git a/clang/lib/Sema/SemaExprObjC.cpp b/clang/lib/Sema/SemaExprObjC.cpp
index d6c656e06ba..818a981b495 100644
--- a/clang/lib/Sema/SemaExprObjC.cpp
+++ b/clang/lib/Sema/SemaExprObjC.cpp
@@ -1946,11 +1946,10 @@ HandleExprPropertyRefExpr(const ObjCObjectPointerType *OPT,
   }
 
   // Attempt to correct for typos in property names.
-  if (TypoCorrection Corrected =
-          CorrectTypo(DeclarationNameInfo(MemberName, MemberLoc),
-                      LookupOrdinaryName, nullptr, nullptr,
-                      llvm::make_unique<DeclFilterCCC<ObjCPropertyDecl>>(),
-                      CTK_ErrorRecovery, IFace, false, OPT)) {
+  DeclFilterCCC<ObjCPropertyDecl> CCC{};
+  if (TypoCorrection Corrected = CorrectTypo(
+          DeclarationNameInfo(MemberName, MemberLoc), LookupOrdinaryName,
+          nullptr, nullptr, CCC, CTK_ErrorRecovery, IFace, false, OPT)) {
     DeclarationName TypoResult = Corrected.getCorrection();
     if (TypoResult.isIdentifier() &&
         TypoResult.getAsIdentifierInfo() == Member) {
@@ -2107,7 +2106,7 @@ ActOnClassPropertyRefExpr(IdentifierInfo &receiverName,
 
 namespace {
 
-class ObjCInterfaceOrSuperCCC : public CorrectionCandidateCallback {
+class ObjCInterfaceOrSuperCCC final : public CorrectionCandidateCallback {
  public:
   ObjCInterfaceOrSuperCCC(ObjCMethodDecl *Method) {
     // Determine whether "super" is acceptable in the current context.
@@ -2119,6 +2118,10 @@ class ObjCInterfaceOrSuperCCC : public CorrectionCandidateCallback {
     return candidate.getCorrectionDeclAs<ObjCInterfaceDecl>() ||
         candidate.isKeyword("super");
   }
+
+  std::unique_ptr<CorrectionCandidateCallback> clone() override {
+    return llvm::make_unique<ObjCInterfaceOrSuperCCC>(*this);
+  }
 };
 
 } // end anonymous namespace
@@ -2194,9 +2197,9 @@ Sema::ObjCMessageKind Sema::getObjCMessageKind(Scope *S,
   }
   }
 
+  ObjCInterfaceOrSuperCCC CCC(getCurMethodDecl());
   if (TypoCorrection Corrected = CorrectTypo(
-          Result.getLookupNameInfo(), Result.getLookupKind(), S, nullptr,
-          llvm::make_unique<ObjCInterfaceOrSuperCCC>(getCurMethodDecl()),
+          Result.getLookupNameInfo(), Result.getLookupKind(), S, nullptr, CCC,
           CTK_ErrorRecovery, nullptr, false, nullptr, false)) {
     if (Corrected.isKeyword()) {
       // If we've found the keyword "super" (the only keyword that would be