[wasm] Fix constant folding with signalling NaN.

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 cc952ecc49bc5fc4476666ba72c8a6e83d945f79..7b28dfbc2746041f31465e187aa80dbab4464a0d 100644
--- a/src/compiler/machine-operator-reducer.cc
+++ b/src/compiler/machine-operator-reducer.cc
@@ -316,14 +316,13 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
     }
     case IrOpcode::kFloat32Sub: {
       Float32BinopMatcher m(node);
-      if (m.right().Is(0) && (copysign(1.0, m.right().Value()) > 0)) {
-        return Replace(m.left().node());  // x - 0 => x
-      }
       if (m.right().IsNaN()) {  // x - NaN => NaN
-        return Replace(m.right().node());
+        // - 0.0 to make a signalling NaN quiet.
+        return ReplaceFloat32(m.right().Value() - 0.0);
       }
       if (m.left().IsNaN()) {  // NaN - x => NaN
-        return Replace(m.left().node());
+        // - 0.0 to make a signalling NaN quiet.
+        return ReplaceFloat32(m.left().Value() - 0.0);
       }
       if (m.IsFoldable()) {  // L - R => (L - R)
         return ReplaceFloat32(m.left().Value() - m.right().Value());
@@ -350,7 +349,8 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
     case IrOpcode::kFloat64Add: {
       Float64BinopMatcher m(node);
       if (m.right().IsNaN()) {  // x + NaN => NaN
-        return Replace(m.right().node());
+        // - 0.0 to make a signalling NaN quiet.
+        return ReplaceFloat64(m.right().Value() - 0.0);
       }
       if (m.IsFoldable()) {  // K + K => K
         return ReplaceFloat64(m.left().Value() + m.right().Value());
@@ -359,14 +359,13 @@ 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
-      }
       if (m.right().IsNaN()) {  // x - NaN => NaN

[titzer, 2017/01/25 13:28:57]

Can you leave a TODO here that we could still do the original strength reduction
if we know the non-zero input was not a signaling NaN (which is AFAICT the case
for normal JS code?)

-        return Replace(m.right().node());
+        // - 0.0 to make a signalling NaN quiet.
+        return ReplaceFloat64(m.right().Value() - 0.0);
       }
       if (m.left().IsNaN()) {  // NaN - x => NaN
-        return Replace(m.left().node());
+        // - 0.0 to make a signalling NaN quiet.
+        return ReplaceFloat64(m.left().Value() - 0.0);
       }
       if (m.IsFoldable()) {  // L - R => (L - R)
         return ReplaceFloat64(m.left().Value() - m.right().Value());
@@ -398,9 +397,9 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
         NodeProperties::ChangeOp(node, machine()->Float64Sub());
         return Changed(node);
       }
-      if (m.right().Is(1)) return Replace(m.left().node());  // x * 1.0 => x
       if (m.right().IsNaN()) {                               // x * NaN => NaN
-        return Replace(m.right().node());
+        // - 0.0 to make a signalling NaN quiet.
+        return ReplaceFloat64(m.right().Value() - 0.0);
       }
       if (m.IsFoldable()) {  // K * K => K
         return ReplaceFloat64(m.left().Value() * m.right().Value());
@@ -414,12 +413,13 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
     }
     case IrOpcode::kFloat64Div: {
       Float64BinopMatcher m(node);
-      if (m.right().Is(1)) return Replace(m.left().node());  // x / 1.0 => x
       if (m.right().IsNaN()) {                               // x / NaN => NaN
-        return Replace(m.right().node());
+        // - 0.0 to make a signalling NaN quiet.
+        return ReplaceFloat64(m.right().Value() - 0.0);
       }
       if (m.left().IsNaN()) {  // NaN / x => NaN
-        return Replace(m.left().node());
+        // - 0.0 to make a signalling NaN quiet.
+        return ReplaceFloat64(m.left().Value() - 0.0);
       }
       if (m.IsFoldable()) {  // K / K => K
         return ReplaceFloat64(m.left().Value() / m.right().Value());