[turbofan][arm64] Match fneg for -0.0 - x pattern.

Note that this patch add an extra bit to the ArchOpcodeField.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/1013743006

Cr-Commit-Position: refs/heads/master@{#27494}

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

@@ -689,6 +689,9 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
                        0, 2);
       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

@@ -85,6 +85,7 @@ namespace compiler {
   V(Arm64Float64Mul)               \
   V(Arm64Float64Div)               \
   V(Arm64Float64Mod)               \
+  V(Arm64Float64Neg)               \
   V(Arm64Float64Sqrt)              \
   V(Arm64Float64RoundDown)         \
   V(Arm64Float64RoundTiesAway)     \

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

@@ -1069,7 +1069,8 @@ void InstructionSelector::VisitFloat64Add(Node* node) {
 void InstructionSelector::VisitFloat64Sub(Node* node) {
   Arm64OperandGenerator g(this);
   Float64BinopMatcher m(node);
-  if (m.left().IsMinusZero() && m.right().IsFloat64RoundDown() &&
+  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))) {
@@ -1081,6 +1082,10 @@ void InstructionSelector::VisitFloat64Sub(Node* node) {
         }
       }
     }
+    Emit(kArm64Float64Neg, g.DefineAsRegister(node),
+         g.UseRegister(m.right().node()));
+    return;
+  }
   VisitRRRFloat64(this, kArm64Float64Sub, node);
 }
 

src/compiler/instruction-codes.h

@@ -127,11 +127,11 @@ typedef int32_t InstructionCode;
 // for code generation. We encode the instruction, addressing mode, and flags
 // continuation into a single InstructionCode which is stored as part of
 // the instruction.
-typedef BitField<ArchOpcode, 0, 7> ArchOpcodeField;
-typedef BitField<AddressingMode, 7, 5> AddressingModeField;
-typedef BitField<FlagsMode, 12, 2> FlagsModeField;
-typedef BitField<FlagsCondition, 14, 4> FlagsConditionField;
-typedef BitField<int, 14, 18> MiscField;
+typedef BitField<ArchOpcode, 0, 8> ArchOpcodeField;
+typedef BitField<AddressingMode, 8, 5> AddressingModeField;
+typedef BitField<FlagsMode, 13, 2> FlagsModeField;
+typedef BitField<FlagsCondition, 15, 4> FlagsConditionField;
+typedef BitField<int, 19, 13> MiscField;
 
 }  // namespace compiler
 }  // namespace internal

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