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

src/compiler/effect-control-linearizer.cc

Index: src/compiler/effect-control-linearizer.cc
diff --git a/src/compiler/effect-control-linearizer.cc b/src/compiler/effect-control-linearizer.cc
index 8701c1923b80c8121efcb371af360bf8eb4fd21d..06618d7c1985fa51e40626129bee8970f78c7e17 100644
--- a/src/compiler/effect-control-linearizer.cc
+++ b/src/compiler/effect-control-linearizer.cc
@@ -1308,6 +1308,7 @@ EffectControlLinearizer::LowerCheckedUint32Mod(Node* node, Node* frame_state,
 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);
@@ -1321,6 +1322,10 @@ EffectControlLinearizer::LowerCheckedInt32Mul(Node* node, Node* frame_state,
 
   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);