[wasm] Remove -0 -x = -x folding because of signalling NaNs.

R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2662363003
Cr-Commit-Position: refs/heads/master@{#42902}

src/compiler/machine-operator-reducer.cc

@@ -331,7 +331,7 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
       if (m.IsFoldable()) {  // L - R => (L - R)
         return ReplaceFloat32(m.left().Value() - m.right().Value());
       }
-      if (m.left().IsMinusZero()) {
+      if (allow_signalling_nan_ && m.left().IsMinusZero()) {
         // -0.0 - round_down(-0.0 - R) => round_up(R)
         if (machine()->Float32RoundUp().IsSupported() &&
             m.right().IsFloat32RoundDown()) {
@@ -378,7 +378,7 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
       if (m.IsFoldable()) {  // L - R => (L - R)
         return ReplaceFloat64(m.left().Value() - m.right().Value());
       }
-      if (m.left().IsMinusZero()) {
+      if (allow_signalling_nan_ && m.left().IsMinusZero()) {
         // -0.0 - round_down(-0.0 - R) => round_up(R)
         if (machine()->Float64RoundUp().IsSupported() &&
             m.right().IsFloat64RoundDown()) {
@@ -437,7 +437,7 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
       if (m.IsFoldable()) {  // K / K => K
         return ReplaceFloat64(m.left().Value() / m.right().Value());
       }
-      if (m.right().Is(-1)) {  // x / -1.0 => -x
+      if (allow_signalling_nan_ && m.right().Is(-1)) {  // x / -1.0 => -x
         node->RemoveInput(1);
         NodeProperties::ChangeOp(node, machine()->Float64Neg());
         return Changed(node);

test/mjsunit/wasm/float-constant-folding.js

@@ -24,6 +24,23 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   assertEquals(0x7fe00000, module.exports.F32Sub0(0x7fa00000));
 })();
 
+(function() {
+  print("F32: -0 sNaN = qNaN");
+  var builder = new WasmModuleBuilder();
+  builder.addFunction("F32Sub0", kSig_i_i)
+    .addBody([
+      kExprF32Const, 0x00, 0x00, 0x00, 0x80, // 0.0
+      kExprGetLocal, 0,
+      kExprF32ReinterpretI32,
+      kExprF32Sub,
+      kExprI32ReinterpretF32,
+            ])
+            .exportFunc();
+  var module = builder.instantiate();
+  // F32Sub0(signalling_NaN)
+  assertEquals(0x7fe00000, module.exports.F32Sub0(0x7fa00000));
+})();
+
 (function() {
   print("F32: sNaN - X = qNaN");
   var builder = new WasmModuleBuilder();
@@ -91,6 +108,25 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   assertEquals(0x7ffa0000, module.exports.F64Sub0());
 })();
 
+(function() {
+  print("F64: -0 - sNaN = qNaN");
+  var builder = new WasmModuleBuilder();
+  builder.addFunction("F64Sub0", kSig_i_i)
+    .addBody([
+      kExprF64Const, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, // 0.0
+      kExprI64Const, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0xf9, 0xff, 0x00,
+      kExprF64ReinterpretI64,
+      kExprF64Sub,
+      kExprI64ReinterpretF64,
+      kExprI64Const, 32,
+      kExprI64ShrU,
+      kExprI32ConvertI64,
+            ])
+            .exportFunc();
+  var module = builder.instantiate();
+  assertEquals(0x7ffa0000, module.exports.F64Sub0());
+})();
+
 (function() {
   print("F64: sNaN - X = qNaN");
   var builder = new WasmModuleBuilder();
@@ -183,6 +219,25 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   assertEquals(0x7ffa0000, module.exports.F64Div1());
 })();
 
+(function() {
+  print("F64: sNaN / -1 = qNaN");
+  var builder = new WasmModuleBuilder();
+  builder.addFunction("F64Div1", kSig_i_i)
+    .addBody([
+      kExprI64Const, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0xf9, 0xff, 0x00,
+      kExprF64ReinterpretI64,
+      kExprF64Const, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xf0, 0xbf,
+      kExprF64Div,
+      kExprI64ReinterpretF64,
+      kExprI64Const, 32,
+      kExprI64ShrU,
+      kExprI32ConvertI64,
+            ])
+            .exportFunc();
+  var module = builder.instantiate();
+  assertEquals(0x7ffa0000, module.exports.F64Div1());
+})();
+
 (function() {
   print("F64: X / sNaN = qNaN");
   var builder = new WasmModuleBuilder();