[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, 19 deletions

diff --git a/clang/lib/Sema/SemaDeclObjC.cpp b/clang/lib/Sema/SemaDeclObjC.cpp
index 76b2129211d..7fa561012ff 100644
--- a/clang/lib/Sema/SemaDeclObjC.cpp
+++ b/clang/lib/Sema/SemaDeclObjC.cpp
@@ -499,7 +499,7 @@ namespace {
 // Callback to only accept typo corrections that are Objective-C classes.
 // If an ObjCInterfaceDecl* is given to the constructor, then the validation
 // function will reject corrections to that class.
-class ObjCInterfaceValidatorCCC : public CorrectionCandidateCallback {
+class ObjCInterfaceValidatorCCC final : public CorrectionCandidateCallback {
  public:
   ObjCInterfaceValidatorCCC() : CurrentIDecl(nullptr) {}
   explicit ObjCInterfaceValidatorCCC(ObjCInterfaceDecl *IDecl)
@@ -510,6 +510,10 @@ class ObjCInterfaceValidatorCCC : public CorrectionCandidateCallback {
     return ID && !declaresSameEntity(ID, CurrentIDecl);
   }
 
+  std::unique_ptr<CorrectionCandidateCallback> clone() override {
+    return llvm::make_unique<ObjCInterfaceValidatorCCC>(*this);
+  }
+
  private:
   ObjCInterfaceDecl *CurrentIDecl;
 };
@@ -549,11 +553,10 @@ ActOnSuperClassOfClassInterface(Scope *S,
   if (!PrevDecl) {
     // Try to correct for a typo in the superclass name without correcting
     // to the class we're defining.
+    ObjCInterfaceValidatorCCC CCC(IDecl);
     if (TypoCorrection Corrected = CorrectTypo(
-            DeclarationNameInfo(SuperName, SuperLoc),
-            LookupOrdinaryName, TUScope,
-            nullptr, llvm::make_unique<ObjCInterfaceValidatorCCC>(IDecl),
-            CTK_ErrorRecovery)) {
+            DeclarationNameInfo(SuperName, SuperLoc), LookupOrdinaryName,
+            TUScope, nullptr, CCC, CTK_ErrorRecovery)) {
       diagnoseTypo(Corrected, PDiag(diag::err_undef_superclass_suggest)
                    << SuperName << ClassName);
       PrevDecl = Corrected.getCorrectionDeclAs<ObjCInterfaceDecl>();
@@ -1292,11 +1295,10 @@ Sema::FindProtocolDeclaration(bool WarnOnDeclarations, bool ForObjCContainer,
   for (const IdentifierLocPair &Pair : ProtocolId) {
     ObjCProtocolDecl *PDecl = LookupProtocol(Pair.first, Pair.second);
     if (!PDecl) {
+      DeclFilterCCC<ObjCProtocolDecl> CCC{};
       TypoCorrection Corrected = CorrectTypo(
-          DeclarationNameInfo(Pair.first, Pair.second),
-          LookupObjCProtocolName, TUScope, nullptr,
-          llvm::make_unique<DeclFilterCCC<ObjCProtocolDecl>>(),
-          CTK_ErrorRecovery);
+          DeclarationNameInfo(Pair.first, Pair.second), LookupObjCProtocolName,
+          TUScope, nullptr, CCC, CTK_ErrorRecovery);
       if ((PDecl = Corrected.getCorrectionDeclAs<ObjCProtocolDecl>()))
         diagnoseTypo(Corrected, PDiag(diag::err_undeclared_protocol_suggest)
                                     << Pair.first);
@@ -1334,7 +1336,8 @@ Sema::FindProtocolDeclaration(bool WarnOnDeclarations, bool ForObjCContainer,
 namespace {
 // Callback to only accept typo corrections that are either
 // Objective-C protocols or valid Objective-C type arguments.
-class ObjCTypeArgOrProtocolValidatorCCC : public CorrectionCandidateCallback {
+class ObjCTypeArgOrProtocolValidatorCCC final
+    : public CorrectionCandidateCallback {
   ASTContext &Context;
   Sema::LookupNameKind LookupKind;
  public:
@@ -1381,6 +1384,10 @@ class ObjCTypeArgOrProtocolValidatorCCC : public CorrectionCandidateCallback {
 
     return false;
   }
+
+  std::unique_ptr<CorrectionCandidateCallback> clone() override {
+    return llvm::make_unique<ObjCTypeArgOrProtocolValidatorCCC>(*this);
+  }
 };
 } // end anonymous namespace
 
@@ -1670,12 +1677,10 @@ void Sema::actOnObjCTypeArgsOrProtocolQualifiers(
     }
 
     // Perform typo correction on the name.
-    TypoCorrection corrected = CorrectTypo(
-        DeclarationNameInfo(identifiers[i], identifierLocs[i]), lookupKind, S,
-        nullptr,
-        llvm::make_unique<ObjCTypeArgOrProtocolValidatorCCC>(Context,
-                                                             lookupKind),
-        CTK_ErrorRecovery);
+    ObjCTypeArgOrProtocolValidatorCCC CCC(Context, lookupKind);
+    TypoCorrection corrected =
+        CorrectTypo(DeclarationNameInfo(identifiers[i], identifierLocs[i]),
+                    lookupKind, S, nullptr, CCC, CTK_ErrorRecovery);
     if (corrected) {
       // Did we find a protocol?
       if (auto proto = corrected.getCorrectionDeclAs<ObjCProtocolDecl>()) {
@@ -1967,9 +1972,10 @@ Decl *Sema::ActOnStartClassImplementation(
   } else {
     // We did not find anything with the name ClassName; try to correct for
     // typos in the class name.
-    TypoCorrection Corrected = CorrectTypo(
-        DeclarationNameInfo(ClassName, ClassLoc), LookupOrdinaryName, TUScope,
-        nullptr, llvm::make_unique<ObjCInterfaceValidatorCCC>(), CTK_NonError);
+    ObjCInterfaceValidatorCCC CCC{};
+    TypoCorrection Corrected =
+        CorrectTypo(DeclarationNameInfo(ClassName, ClassLoc),
+                    LookupOrdinaryName, TUScope, nullptr, CCC, CTK_NonError);
     if (Corrected.getCorrectionDeclAs<ObjCInterfaceDecl>()) {
       // Suggest the (potentially) correct interface name. Don't provide a
       // code-modification hint or use the typo name for recovery, because