[turbofan] Lower "-0.0 - x" in the MachineOperatorReducer.

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 55c93c2c13d826876be71fa9c60b36e14a9f8156..c1c58fe90404b75bc235607fa5ccf625b5e0ba0f 100644
--- a/src/compiler/machine-operator-reducer.cc
+++ b/src/compiler/machine-operator-reducer.cc
@@ -314,6 +314,39 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
       if (m.LeftEqualsRight()) return ReplaceBool(true);  // x <= x => true
       break;
     }
+    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());
+      }
+      if (m.left().IsNaN()) {  // NaN - x => NaN
+        return Replace(m.left().node());
+      }
+      if (m.IsFoldable()) {  // L - R => (L - R)
+        return ReplaceFloat32(m.left().Value() - m.right().Value());
+      }
+      if (m.left().IsMinusZero()) {
+        // -0.0 - round_down(-0.0 - R) => round_up(R)
+        if (machine()->Float32RoundUp().IsSupported() &&
+            m.right().IsFloat32RoundDown()) {
+          if (m.right().InputAt(0)->opcode() == IrOpcode::kFloat32Sub) {
+            Float32BinopMatcher mright0(m.right().InputAt(0));
+            if (mright0.left().IsMinusZero()) {
+              return Replace(graph()->NewNode(machine()->Float32RoundUp().op(),
+                                              mright0.right().node()));
+            }
+          }
+        }
+        // -0.0 - R => -R
+        node->RemoveInput(0);
+        NodeProperties::ChangeOp(node, machine()->Float32Neg());
+        return Changed(node);
+      }
+      break;
+    }
     case IrOpcode::kFloat64Add: {
       Float64BinopMatcher m(node);
       if (m.right().IsNaN()) {  // x + NaN => NaN
@@ -335,9 +368,26 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
       if (m.left().IsNaN()) {  // NaN - x => NaN
         return Replace(m.left().node());
       }
-      if (m.IsFoldable()) {  // K - K => K
+      if (m.IsFoldable()) {  // L - R => (L - R)
         return ReplaceFloat64(m.left().Value() - m.right().Value());
       }
+      if (m.left().IsMinusZero()) {
+        // -0.0 - round_down(-0.0 - R) => round_up(R)
+        if (machine()->Float64RoundUp().IsSupported() &&
+            m.right().IsFloat64RoundDown()) {
+          if (m.right().InputAt(0)->opcode() == IrOpcode::kFloat64Sub) {
+            Float64BinopMatcher mright0(m.right().InputAt(0));
+            if (mright0.left().IsMinusZero()) {
+              return Replace(graph()->NewNode(machine()->Float64RoundUp().op(),
+                                              mright0.right().node()));
+            }
+          }
+        }
+        // -0.0 - R => -R
+        node->RemoveInput(0);
+        NodeProperties::ChangeOp(node, machine()->Float64Neg());
+        return Changed(node);
+      }
       break;
     }
     case IrOpcode::kFloat64Mul: {