[stubs] Allow branch combining for Smi overflow checks.

src/code-stubs.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/code-stubs.h"
 
 #include <sstream>
 
 #include "src/bootstrapper.h"
 #include "src/code-factory.h"
@@ skipping 537 matching lines @@
 
     assembler->Bind(&if_lhsissmi);
     {
       // Check if the {rhs} is also a Smi.
       Label if_rhsissmi(assembler), if_rhsisnotsmi(assembler);
       assembler->Branch(assembler->WordIsSmi(rhs), &if_rhsissmi,
                         &if_rhsisnotsmi);
 
       assembler->Bind(&if_rhsissmi);
       {
-        // TODO(bmeurer): Properly fuse Int64AddWithOverflow on x64
+        // Try fast Smi addition first.
         Node* pair = assembler->SmiAddWithOverflow(lhs, rhs);
-        Node* result = assembler->Projection(0, pair);
         Node* overflow = assembler->Projection(1, pair);
 
+        // Check if the Smi additon overflowed.
         Label if_overflow(assembler), if_notoverflow(assembler);
         assembler->Branch(overflow, &if_overflow, &if_notoverflow);
 
         assembler->Bind(&if_overflow);
         {
           var_fadd_lhs.Bind(assembler->SmiToFloat64(lhs));
           var_fadd_rhs.Bind(assembler->SmiToFloat64(rhs));
           assembler->Goto(&do_fadd);
         }
 
         assembler->Bind(&if_notoverflow);
-        assembler->Return(result);
+        assembler->Return(assembler->Projection(0, pair));
       }
 
       assembler->Bind(&if_rhsisnotsmi);
       {
         // Load the map of {rhs}.
         Node* rhs_map = assembler->LoadObjectField(rhs, HeapObject::kMapOffset);
 
         // Check if the {rhs} is a HeapNumber.
         Label if_rhsisnumber(assembler),
             if_rhsisnotnumber(assembler, Label::kDeferred);
@@ skipping 327 matching lines @@
     {
       // Check if the {rhs} is also a Smi.
       Label if_rhsissmi(assembler), if_rhsisnotsmi(assembler);
       assembler->Branch(assembler->WordIsSmi(rhs), &if_rhsissmi,
                         &if_rhsisnotsmi);
 
       assembler->Bind(&if_rhsissmi);
       {
         // Try a fast Smi subtraction first.
         Node* pair = assembler->SmiSubWithOverflow(lhs, rhs);
-        Node* result = assembler->Projection(0, pair);
         Node* overflow = assembler->Projection(1, pair);
 
         // Check if the Smi subtraction overflowed.
         Label if_overflow(assembler), if_notoverflow(assembler);
         assembler->Branch(overflow, &if_overflow, &if_notoverflow);
 
         assembler->Bind(&if_overflow);
         {
           // The result doesn't fit into Smi range.
           var_fsub_lhs.Bind(assembler->SmiToFloat64(lhs));
           var_fsub_rhs.Bind(assembler->SmiToFloat64(rhs));
           assembler->Goto(&do_fsub);
         }
 
         assembler->Bind(&if_notoverflow);
-        assembler->Return(result);
+        assembler->Return(assembler->Projection(0, pair));
       }
 
       assembler->Bind(&if_rhsisnotsmi);
       {
         // Load the map of the {rhs}.
         Node* rhs_map = assembler->LoadMap(rhs);
 
         // Check if {rhs} is a HeapNumber.
         Label if_rhsisnumber(assembler),
             if_rhsisnotnumber(assembler, Label::kDeferred);
@@ skipping 2402 matching lines @@
   if (type->Is(Type::UntaggedPointer())) {
     return Representation::External();
   }
 
   DCHECK(!type->Is(Type::Untagged()));
   return Representation::Tagged();
 }
 
 }  // namespace internal
 }  // namespace v8