Reland "Match fneg for -0.0 - x pattern."

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/1040053002

Cr-Commit-Position: refs/heads/master@{#27516}

src/compiler/arm64/code-generator-arm64.cc

@@ -726,6 +726,9 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       __ Fmin(i.OutputDoubleRegister(), i.InputDoubleRegister(0),
               i.InputDoubleRegister(1));
       break;
+    case kArm64Float64Neg:
+      __ Fneg(i.OutputDoubleRegister(), i.InputDoubleRegister(0));
+      break;
     case kArm64Float64Sqrt:
       __ Fsqrt(i.OutputDoubleRegister(), i.InputDoubleRegister(0));
       break;

src/compiler/arm64/instruction-codes-arm64.h

@@ -94,6 +94,7 @@ namespace compiler {
   V(Arm64Float64Mod)               \
   V(Arm64Float64Max)               \
   V(Arm64Float64Min)               \
+  V(Arm64Float64Neg)               \
   V(Arm64Float64Sqrt)              \
   V(Arm64Float64RoundDown)         \
   V(Arm64Float64RoundTiesAway)     \

src/compiler/arm64/instruction-selector-arm64.cc

@@ -1060,17 +1060,22 @@ void InstructionSelector::VisitFloat32Sub(Node* node) {
 void InstructionSelector::VisitFloat64Sub(Node* node) {
   Arm64OperandGenerator g(this);
   Float64BinopMatcher m(node);
-  if (m.left().IsMinusZero() && m.right().IsFloat64RoundDown() &&
-      CanCover(m.node(), m.right().node())) {
-    if (m.right().InputAt(0)->opcode() == IrOpcode::kFloat64Sub &&
-        CanCover(m.right().node(), m.right().InputAt(0))) {
-      Float64BinopMatcher mright0(m.right().InputAt(0));
-      if (mright0.left().IsMinusZero()) {
-        Emit(kArm64Float64RoundUp, g.DefineAsRegister(node),
-             g.UseRegister(mright0.right().node()));
-        return;
+  if (m.left().IsMinusZero()) {
+    if (m.right().IsFloat64RoundDown() &&
+        CanCover(m.node(), m.right().node())) {
+      if (m.right().InputAt(0)->opcode() == IrOpcode::kFloat64Sub &&
+          CanCover(m.right().node(), m.right().InputAt(0))) {
+        Float64BinopMatcher mright0(m.right().InputAt(0));
+        if (mright0.left().IsMinusZero()) {
+          Emit(kArm64Float64RoundUp, g.DefineAsRegister(node),
+               g.UseRegister(mright0.right().node()));
+          return;
+        }
       }
     }
+    Emit(kArm64Float64Neg, g.DefineAsRegister(node),
+         g.UseRegister(m.right().node()));
+    return;
   }
   VisitRRR(this, kArm64Float64Sub, node);
 }

test/unittests/compiler/arm64/instruction-selector-arm64-unittest.cc

@@ -2257,6 +2257,21 @@ TEST_F(InstructionSelectorTest, Word32Clz) {
   EXPECT_EQ(s.ToVreg(n), s.ToVreg(s[0]->Output()));
 }
 
+
+TEST_F(InstructionSelectorTest, Float64SubWithMinusZero) {
+  StreamBuilder m(this, kMachFloat64, kMachFloat64);
+  Node* const p0 = m.Parameter(0);
+  Node* const n = m.Float64Sub(m.Float64Constant(-0.0), p0);
+  m.Return(n);
+  Stream s = m.Build();
+  ASSERT_EQ(1U, s.size());
+  EXPECT_EQ(kArm64Float64Neg, s[0]->arch_opcode());
+  ASSERT_EQ(1U, s[0]->InputCount());
+  EXPECT_EQ(s.ToVreg(p0), s.ToVreg(s[0]->InputAt(0)));
+  ASSERT_EQ(1U, s[0]->OutputCount());
+  EXPECT_EQ(s.ToVreg(n), s.ToVreg(s[0]->Output()));
+}
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8