[Turbofan]: Eliminate the check for -0 if it's not possible/observable.

src/compiler/effect-control-linearizer.cc

 // Copyright 2015 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/compiler/effect-control-linearizer.h"
 
 #include "src/code-factory.h"
 #include "src/compiler/access-builder.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/linkage.h"
@@ skipping 1290 matching lines @@
 
   // Perform the actual unsigned integer modulus.
   Node* value = graph()->NewNode(machine()->Uint32Mod(), lhs, rhs, control);
 
   return ValueEffectControl(value, effect, control);
 }
 
 EffectControlLinearizer::ValueEffectControl
 EffectControlLinearizer::LowerCheckedInt32Mul(Node* node, Node* frame_state,
                                               Node* effect, Node* control) {
+  CheckForMinusZeroMode mode = CheckMinusZeroModeOf(node->op());
   Node* zero = jsgraph()->Int32Constant(0);
   Node* lhs = node->InputAt(0);
   Node* rhs = node->InputAt(1);
 
   Node* projection =
       graph()->NewNode(machine()->Int32MulWithOverflow(), lhs, rhs, control);
 
   Node* check = graph()->NewNode(common()->Projection(1), projection, control);
   control = effect = graph()->NewNode(common()->DeoptimizeIf(), check,
                                       frame_state, effect, control);
 
   Node* value = graph()->NewNode(common()->Projection(0), projection, control);
 
+  if (mode == CheckForMinusZeroMode::kDontCheckForMinusZero) {

[Benedikt Meurer, 2016/07/17 17:44:07]

Nit: I'd prefer a positive check here, i.e.

if (mode == CheckForMinusZeroMode::kCheckForMinusZero) {
  ...
}
return ValueEffectControl(value, effect, control);

[mvstanton, 2016/07/18 08:48:58]

Done.

+    return ValueEffectControl(value, effect, control);
+  }
+
   Node* check_zero = graph()->NewNode(machine()->Word32Equal(), value, zero);
   Node* branch_zero = graph()->NewNode(common()->Branch(BranchHint::kFalse),
                                        check_zero, control);
 
   Node* if_zero = graph()->NewNode(common()->IfTrue(), branch_zero);
   Node* e_if_zero = effect;
   {
     // We may need to return negative zero.
     Node* or_inputs = graph()->NewNode(machine()->Word32Or(), lhs, rhs);
     Node* check_or =
@@ skipping 774 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kNoThrow);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8