[turbofan] add some simplifications in the machine operator reducer

src/compiler/machine-operator-reducer.cc

Index: src/compiler/machine-operator-reducer.cc
diff --git a/src/compiler/machine-operator-reducer.cc b/src/compiler/machine-operator-reducer.cc
index 932854778eaeacf8c73b5f0bd439a83cedde7862..098e4d03e11493ba2bf79fd32f95d86d3347de1c 100644
--- a/src/compiler/machine-operator-reducer.cc
+++ b/src/compiler/machine-operator-reducer.cc
@@ -338,6 +338,9 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
     }
     case IrOpcode::kFloat64Add: {
       Float64BinopMatcher m(node);
+      if (m.right().IsNaN()) {  // x + NaN => NaN
+        return Replace(m.right().node());
+      }
       if (m.IsFoldable()) {  // K + K => K
         return ReplaceFloat64(m.left().Value() + m.right().Value());
       }
@@ -345,6 +348,15 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
     }
     case IrOpcode::kFloat64Sub: {
       Float64BinopMatcher m(node);
+      if (m.right().Is(0) && (Double(m.right().Value()).Sign() > 0)) {
+        return Replace(m.left().node());  // x - 0 => x

[titzer, 2014/09/25 09:08:41]

Is this correct if left is -0?

[vincent.belliard, 2014/09/25 09:51:18]

Yes. the result is unchanged (except that NaN are normalized on Arm and Arm64).
On Arm and Arm64, we use a subtraction by zero to normalize NaNs.
asm.js use a subtraction by zero to force a number.

+      }
+      if (m.right().IsNaN()) {  // x - NaN => NaN
+        return Replace(m.right().node());
+      }
+      if (m.left().IsNaN()) {  // NaN - x => NaN
+        return Replace(m.left().node());
+      }
       if (m.IsFoldable()) {  // K - K => K
         return ReplaceFloat64(m.left().Value() - m.right().Value());
       }
@@ -377,6 +389,9 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
     }
     case IrOpcode::kFloat64Mod: {
       Float64BinopMatcher m(node);
+      if (m.right().Is(0)) {  // x % 0 => NaN
+        return ReplaceFloat64(base::OS::nan_value());
+      }
       if (m.right().IsNaN()) {  // x % NaN => NaN
         return Replace(m.right().node());
       }