[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



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@356925 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 21 deletions

diff --git a/lib/Sema/SemaLookup.cpp b/lib/Sema/SemaLookup.cpp
index 86960e0a1d..f27a9591dd 100644
--- a/lib/Sema/SemaLookup.cpp
+++ b/lib/Sema/SemaLookup.cpp
@@ -4572,8 +4572,7 @@ static void AddKeywordsToConsumer(Sema &SemaRef,
 
 std::unique_ptr<TypoCorrectionConsumer> Sema::makeTypoCorrectionConsumer(
     const DeclarationNameInfo &TypoName, Sema::LookupNameKind LookupKind,
-    Scope *S, CXXScopeSpec *SS,
-    std::unique_ptr<CorrectionCandidateCallback> CCC,
+    Scope *S, CXXScopeSpec *SS, CorrectionCandidateCallback &CCC,
     DeclContext *MemberContext, bool EnteringContext,
     const ObjCObjectPointerType *OPT, bool ErrorRecovery) {
 
@@ -4635,9 +4634,13 @@ std::unique_ptr<TypoCorrectionConsumer> Sema::makeTypoCorrectionConsumer(
                                            TypoName.getBeginLoc());
   }
 
-  CorrectionCandidateCallback &CCCRef = *CCC;
+  // Extend the lifetime of the callback. We delayed this until here
+  // to avoid allocations in the hot path (which is where no typo correction
+  // occurs). Note that CorrectionCandidateCallback is polymorphic and
+  // initially stack-allocated.
+  std::unique_ptr<CorrectionCandidateCallback> ClonedCCC = CCC.clone();
   auto Consumer = llvm::make_unique<TypoCorrectionConsumer>(
-      *this, TypoName, LookupKind, S, SS, std::move(CCC), MemberContext,
+      *this, TypoName, LookupKind, S, SS, std::move(ClonedCCC), MemberContext,
       EnteringContext);
 
   // Perform name lookup to find visible, similarly-named entities.
@@ -4689,7 +4692,9 @@ std::unique_ptr<TypoCorrectionConsumer> Sema::makeTypoCorrectionConsumer(
     }
   }
 
-  AddKeywordsToConsumer(*this, *Consumer, S, CCCRef, SS && SS->isNotEmpty());
+  AddKeywordsToConsumer(*this, *Consumer, S,
+                        *Consumer->getCorrectionValidator(),
+                        SS && SS->isNotEmpty());
 
   // Build the NestedNameSpecifiers for the KnownNamespaces, if we're going
   // to search those namespaces.
@@ -4743,19 +4748,18 @@ std::unique_ptr<TypoCorrectionConsumer> Sema::makeTypoCorrectionConsumer(
 TypoCorrection Sema::CorrectTypo(const DeclarationNameInfo &TypoName,
                                  Sema::LookupNameKind LookupKind,
                                  Scope *S, CXXScopeSpec *SS,
-                                 std::unique_ptr<CorrectionCandidateCallback> CCC,
+                                 CorrectionCandidateCallback &CCC,
                                  CorrectTypoKind Mode,
                                  DeclContext *MemberContext,
                                  bool EnteringContext,
                                  const ObjCObjectPointerType *OPT,
                                  bool RecordFailure) {
-  assert(CCC && "CorrectTypo requires a CorrectionCandidateCallback");
-
   // Always let the ExternalSource have the first chance at correction, even
   // if we would otherwise have given up.
   if (ExternalSource) {
-    if (TypoCorrection Correction = ExternalSource->CorrectTypo(
-        TypoName, LookupKind, S, SS, *CCC, MemberContext, EnteringContext, OPT))
+    if (TypoCorrection Correction =
+            ExternalSource->CorrectTypo(TypoName, LookupKind, S, SS, CCC,
+                                        MemberContext, EnteringContext, OPT))
       return Correction;
   }
 
@@ -4763,12 +4767,12 @@ TypoCorrection Sema::CorrectTypo(const DeclarationNameInfo &TypoName,
   // WantObjCSuper is only true for CTC_ObjCMessageReceiver and for
   // some instances of CTC_Unknown, while WantRemainingKeywords is true
   // for CTC_Unknown but not for CTC_ObjCMessageReceiver.
-  bool ObjCMessageReceiver = CCC->WantObjCSuper && !CCC->WantRemainingKeywords;
+  bool ObjCMessageReceiver = CCC.WantObjCSuper && !CCC.WantRemainingKeywords;
 
   IdentifierInfo *Typo = TypoName.getName().getAsIdentifierInfo();
-  auto Consumer = makeTypoCorrectionConsumer(
-      TypoName, LookupKind, S, SS, std::move(CCC), MemberContext,
-      EnteringContext, OPT, Mode == CTK_ErrorRecovery);
+  auto Consumer = makeTypoCorrectionConsumer(TypoName, LookupKind, S, SS, CCC,
+                                             MemberContext, EnteringContext,
+                                             OPT, Mode == CTK_ErrorRecovery);
 
   if (!Consumer)
     return TypoCorrection();
@@ -4878,16 +4882,13 @@ TypoCorrection Sema::CorrectTypo(const DeclarationNameInfo &TypoName,
 /// needed.
 TypoExpr *Sema::CorrectTypoDelayed(
     const DeclarationNameInfo &TypoName, Sema::LookupNameKind LookupKind,
-    Scope *S, CXXScopeSpec *SS,
-    std::unique_ptr<CorrectionCandidateCallback> CCC,
+    Scope *S, CXXScopeSpec *SS, CorrectionCandidateCallback &CCC,
     TypoDiagnosticGenerator TDG, TypoRecoveryCallback TRC, CorrectTypoKind Mode,
     DeclContext *MemberContext, bool EnteringContext,
     const ObjCObjectPointerType *OPT) {
-  assert(CCC && "CorrectTypoDelayed requires a CorrectionCandidateCallback");
-
-  auto Consumer = makeTypoCorrectionConsumer(
-      TypoName, LookupKind, S, SS, std::move(CCC), MemberContext,
-      EnteringContext, OPT, Mode == CTK_ErrorRecovery);
+  auto Consumer = makeTypoCorrectionConsumer(TypoName, LookupKind, S, SS, CCC,
+                                             MemberContext, EnteringContext,
+                                             OPT, Mode == CTK_ErrorRecovery);
 
   // Give the external sema source a chance to correct the typo.
   TypoCorrection ExternalTypo;