[Sema] Avoid CallExpr::setNumArgs in Sema::BuildCallToObjectOfClassType

[riccibruno]

Summary

CallExpr::setNumArgs is the only thing that prevents storing the arguments
of a call expression in a trailing array since it might resize the argument array.
setNumArgs is only called in 3 places in Sema, and for all of them it is
possible to avoid it.

This deals with the call to setNumArgs in BuildCallToObjectOfClassType.
Instead of constructing the CXXOperatorCallExpr first and later calling
setNumArgs if we have default arguments, we first construct a large
enough SmallVector, do the promotion/check of the arguments, and
then construct the CXXOperatorCallExpr.

Incidentally this also avoid reallocating the arguments when the
call operator has default arguments but this is not the primary goal.

[aaron.ballman]

lib/Sema/SemaOverload.cpp

13260 ↗

(On Diff #175247)

arguments -> argument

Also, I think this comment can be re-flowed to condense it.

13308 ↗

(On Diff #175247)

Formatting is off here.

13318 ↗

(On Diff #175247)

Here as well.

[riccibruno]

fixed the formatting

[aaron.ballman]

LGTM!

cfe/trunk/lib/Sema/SemaOverload.cpp

Sema::BuildCallToObjectOfClassType(Scope *S, Expr *Obj,
   OpLocInfo.setCXXOperatorNameRange(SourceRange(LParenLoc, RParenLoc));
   ExprResult NewFn = CreateFunctionRefExpr(*this, Method, Best->FoundDecl,
                                            Obj, HadMultipleCandidates,
                                            OpLocInfo.getLoc(),
                                            OpLocInfo.getInfo());
   if (NewFn.isInvalid())
     return true;
 
+  // The number of argument slots to allocate in the call. If we have default
+  // arguments we need to allocate space for them as well. We additionally
+  // need one more slot for the object parameter.
+  unsigned NumArgsSlots = 1 + std::max<unsigned>(Args.size(), NumParams);
+
   // Build the full argument list for the method call (the implicit object
   // parameter is placed at the beginning of the list).
-  SmallVector<Expr *, 8> MethodArgs(Args.size() + 1);
-  MethodArgs[0] = Object.get();
-  std::copy(Args.begin(), Args.end(), MethodArgs.begin() + 1);
-
-  // Once we've built TheCall, all of the expressions are properly
-  // owned.
-  QualType ResultTy = Method->getReturnType();
-  ExprValueKind VK = Expr::getValueKindForType(ResultTy);
-  ResultTy = ResultTy.getNonLValueExprType(Context);
-
-  CXXOperatorCallExpr *TheCall = new (Context)
-      CXXOperatorCallExpr(Context, OO_Call, NewFn.get(), MethodArgs, ResultTy,
-                          VK, RParenLoc, FPOptions());
-
-  if (CheckCallReturnType(Method->getReturnType(), LParenLoc, TheCall, Method))
-    return true;
-
-  // We may have default arguments. If so, we need to allocate more
-  // slots in the call for them.
-  if (Args.size() < NumParams)
-    TheCall->setNumArgs(Context, NumParams + 1);
+  SmallVector<Expr *, 8> MethodArgs(NumArgsSlots);
 
   bool IsError = false;
 
   // Initialize the implicit object parameter.
   ExprResult ObjRes =
     PerformObjectArgumentInitialization(Object.get(), /*Qualifier=*/nullptr,
                                         Best->FoundDecl, Method);
   if (ObjRes.isInvalid())
     IsError = true;
   else
     Object = ObjRes;
-  TheCall->setArg(0, Object.get());
+  MethodArgs[0] = Object.get();
 
   // Check the argument types.
   for (unsigned i = 0; i != NumParams; i++) {
     Expr *Arg;
     if (i < Args.size()) {
       Arg = Args[i];
 
       // Pass the argument.
if (i < Args.size()) {
       if (DefArg.isInvalid()) {
         IsError = true;
         break;
       }
 
       Arg = DefArg.getAs<Expr>();
     }
 
-    TheCall->setArg(i + 1, Arg);
+    MethodArgs[i + 1] = Arg;
   }
 
   // If this is a variadic call, handle args passed through "...".
   if (Proto->isVariadic()) {
     // Promote the arguments (C99 6.5.2.2p7).
     for (unsigned i = NumParams, e = Args.size(); i < e; i++) {
       ExprResult Arg = DefaultVariadicArgumentPromotion(Args[i], VariadicMethod,
                                                         nullptr);
       IsError |= Arg.isInvalid();
-      TheCall->setArg(i + 1, Arg.get());
+      MethodArgs[i + 1] = Arg.get();
     }
   }
 
-  if (IsError) return true;
+  if (IsError)
+    return true;
 
   DiagnoseSentinelCalls(Method, LParenLoc, Args);
 
+  // Once we've built TheCall, all of the expressions are properly owned.
+  QualType ResultTy = Method->getReturnType();
+  ExprValueKind VK = Expr::getValueKindForType(ResultTy);
+  ResultTy = ResultTy.getNonLValueExprType(Context);
+
+  CXXOperatorCallExpr *TheCall = new (Context)
+      CXXOperatorCallExpr(Context, OO_Call, NewFn.get(), MethodArgs, ResultTy,
+                          VK, RParenLoc, FPOptions());
+
+  if (CheckCallReturnType(Method->getReturnType(), LParenLoc, TheCall, Method))
+    return true;
+
   if (CheckFunctionCall(Method, TheCall, Proto))
     return true;
 
   return MaybeBindToTemporary(TheCall);
 }
 
 /// BuildOverloadedArrowExpr - Build a call to an overloaded @c operator->
 ///  (if one exists), where @c Base is an expression of class type and