[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, 16 insertions, 19 deletions

diff --git a/lib/Sema/SemaOverload.cpp b/lib/Sema/SemaOverload.cpp
index 2f6f94313b..eea9298a56 100644
--- a/lib/Sema/SemaOverload.cpp
+++ b/lib/Sema/SemaOverload.cpp
@@ -11892,15 +11892,6 @@ public:
 
 }
 
-static std::unique_ptr<CorrectionCandidateCallback>
-MakeValidator(Sema &SemaRef, MemberExpr *ME, size_t NumArgs,
-              bool HasTemplateArgs, bool AllowTypoCorrection) {
-  if (!AllowTypoCorrection)
-    return llvm::make_unique<NoTypoCorrectionCCC>();
-  return llvm::make_unique<FunctionCallFilterCCC>(SemaRef, NumArgs,
-                                                  HasTemplateArgs, ME);
-}
-
 /// Attempts to recover from a call where no functions were found.
 ///
 /// Returns true if new candidates were found.
@@ -11935,16 +11926,22 @@ BuildRecoveryCallExpr(Sema &SemaRef, Scope *S, Expr *Fn,
   LookupResult R(SemaRef, ULE->getName(), ULE->getNameLoc(),
                  Sema::LookupOrdinaryName);
   bool DoDiagnoseEmptyLookup = EmptyLookup;
-  if (!DiagnoseTwoPhaseLookup(SemaRef, Fn->getExprLoc(), SS, R,
-                              OverloadCandidateSet::CSK_Normal,
-                              ExplicitTemplateArgs, Args,
-                              &DoDiagnoseEmptyLookup) &&
-    (!DoDiagnoseEmptyLookup || SemaRef.DiagnoseEmptyLookup(
-        S, SS, R,
-        MakeValidator(SemaRef, dyn_cast<MemberExpr>(Fn), Args.size(),
-                      ExplicitTemplateArgs != nullptr, AllowTypoCorrection),
-        ExplicitTemplateArgs, Args)))
-    return ExprError();
+  if (!DiagnoseTwoPhaseLookup(
+          SemaRef, Fn->getExprLoc(), SS, R, OverloadCandidateSet::CSK_Normal,
+          ExplicitTemplateArgs, Args, &DoDiagnoseEmptyLookup)) {
+    NoTypoCorrectionCCC NoTypoValidator{};
+    FunctionCallFilterCCC FunctionCallValidator(SemaRef, Args.size(),
+                                                ExplicitTemplateArgs != nullptr,
+                                                dyn_cast<MemberExpr>(Fn));
+    CorrectionCandidateCallback &Validator =
+        AllowTypoCorrection
+            ? static_cast<CorrectionCandidateCallback &>(FunctionCallValidator)
+            : static_cast<CorrectionCandidateCallback &>(NoTypoValidator);
+    if (!DoDiagnoseEmptyLookup ||
+        SemaRef.DiagnoseEmptyLookup(S, SS, R, Validator, ExplicitTemplateArgs,
+                                    Args))
+      return ExprError();
+  }
 
   assert(!R.empty() && "lookup results empty despite recovery");