[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, 25 insertions, 15 deletions

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 55e176f4c7d..9f9e117ab9f 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -3781,7 +3781,7 @@ namespace {
 
 // Callback to only accept typo corrections that can be a valid C++ member
 // intializer: either a non-static field member or a base class.
-class MemInitializerValidatorCCC : public CorrectionCandidateCallback {
+class MemInitializerValidatorCCC final : public CorrectionCandidateCallback {
 public:
   explicit MemInitializerValidatorCCC(CXXRecordDecl *ClassDecl)
       : ClassDecl(ClassDecl) {}
@@ -3795,6 +3795,10 @@ public:
     return false;
   }
 
+  std::unique_ptr<CorrectionCandidateCallback> clone() override {
+    return llvm::make_unique<MemInitializerValidatorCCC>(*this);
+  }
+
 private:
   CXXRecordDecl *ClassDecl;
 };
@@ -3924,11 +3928,10 @@ Sema::BuildMemInitializer(Decl *ConstructorD,
 
       // If no results were found, try to correct typos.
       TypoCorrection Corr;
+      MemInitializerValidatorCCC CCC(ClassDecl);
       if (R.empty() && BaseType.isNull() &&
-          (Corr = CorrectTypo(
-               R.getLookupNameInfo(), R.getLookupKind(), S, &SS,
-               llvm::make_unique<MemInitializerValidatorCCC>(ClassDecl),
-               CTK_ErrorRecovery, ClassDecl))) {
+          (Corr = CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), S, &SS,
+                              CCC, CTK_ErrorRecovery, ClassDecl))) {
         if (FieldDecl *Member = Corr.getCorrectionDeclAs<FieldDecl>()) {
           // We have found a non-static data member with a similar
           // name to what was typed; complain and initialize that
@@ -9353,13 +9356,17 @@ static bool IsUsingDirectiveInToplevelContext(DeclContext *CurContext) {
 namespace {
 
 // Callback to only accept typo corrections that are namespaces.
-class NamespaceValidatorCCC : public CorrectionCandidateCallback {
+class NamespaceValidatorCCC final : public CorrectionCandidateCallback {
 public:
   bool ValidateCandidate(const TypoCorrection &candidate) override {
     if (NamedDecl *ND = candidate.getCorrectionDecl())
       return isa<NamespaceDecl>(ND) || isa<NamespaceAliasDecl>(ND);
     return false;
   }
+
+  std::unique_ptr<CorrectionCandidateCallback> clone() override {
+    return llvm::make_unique<NamespaceValidatorCCC>(*this);
+  }
 };
 
 }
@@ -9369,9 +9376,9 @@ static bool TryNamespaceTypoCorrection(Sema &S, LookupResult &R, Scope *Sc,
                                        SourceLocation IdentLoc,
                                        IdentifierInfo *Ident) {
   R.clear();
+  NamespaceValidatorCCC CCC{};
   if (TypoCorrection Corrected =
-          S.CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), Sc, &SS,
-                        llvm::make_unique<NamespaceValidatorCCC>(),
+          S.CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), Sc, &SS, CCC,
                         Sema::CTK_ErrorRecovery)) {
     if (DeclContext *DC = S.computeDeclContext(SS, false)) {
       std::string CorrectedStr(Corrected.getAsString(S.getLangOpts()));
@@ -9866,7 +9873,7 @@ static CXXBaseSpecifier *findDirectBaseWithType(CXXRecordDecl *Derived,
 }
 
 namespace {
-class UsingValidatorCCC : public CorrectionCandidateCallback {
+class UsingValidatorCCC final : public CorrectionCandidateCallback {
 public:
   UsingValidatorCCC(bool HasTypenameKeyword, bool IsInstantiation,
                     NestedNameSpecifier *NNS, CXXRecordDecl *RequireMemberOf)
@@ -9936,6 +9943,10 @@ public:
     return !HasTypenameKeyword;
   }
 
+  std::unique_ptr<CorrectionCandidateCallback> clone() override {
+    return llvm::make_unique<UsingValidatorCCC>(*this);
+  }
+
 private:
   bool HasTypenameKeyword;
   bool IsInstantiation;
@@ -10092,12 +10103,11 @@ NamedDecl *Sema::BuildUsingDeclaration(
         isa<TranslationUnitDecl>(LookupContext) &&
         getSourceManager().isInSystemHeader(UsingLoc))
       return nullptr;
-    if (TypoCorrection Corrected = CorrectTypo(
-            R.getLookupNameInfo(), R.getLookupKind(), S, &SS,
-            llvm::make_unique<UsingValidatorCCC>(
-                HasTypenameKeyword, IsInstantiation, SS.getScopeRep(),
-                dyn_cast<CXXRecordDecl>(CurContext)),
-            CTK_ErrorRecovery)) {
+    UsingValidatorCCC CCC(HasTypenameKeyword, IsInstantiation, SS.getScopeRep(),
+                          dyn_cast<CXXRecordDecl>(CurContext));
+    if (TypoCorrection Corrected =
+            CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), S, &SS, CCC,
+                        CTK_ErrorRecovery)) {
       // We reject candidates where DroppedSpecifier == true, hence the
       // literal '0' below.
       diagnoseTypo(Corrected, PDiag(diag::err_no_member_suggest)