[turbofan] ARM64: Use zr to store immediate zero

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

Index: src/compiler/arm64/instruction-selector-arm64.cc
diff --git a/src/compiler/arm64/instruction-selector-arm64.cc b/src/compiler/arm64/instruction-selector-arm64.cc
index 7114077ff9a86328142000c3e3fc84c2936191ee..f95fd7e811c9b037f2715d040574d57524b6575c 100644
--- a/src/compiler/arm64/instruction-selector-arm64.cc
+++ b/src/compiler/arm64/instruction-selector-arm64.cc
@@ -40,7 +40,9 @@ class Arm64OperandGenerator final : public OperandGenerator {
   // Use the zero register if the node has the immediate value zero, otherwise
   // assign a register.
   InstructionOperand UseRegisterOrImmediateZero(Node* node) {
-    if (IsIntegerConstant(node) && (GetIntegerConstantValue(node) == 0)) {
+    if ((IsIntegerConstant(node) && (GetIntegerConstantValue(node) == 0)) ||
+        (IsFloatConstant(node) && (GetFloatConstantValue(node) == 0.0) &&
+         (copysign(1.0, GetFloatConstantValue(node)) > 0.0))) {

[Benedikt Meurer, 2016/05/03 17:33:20]

Use std::signbit here, or even easier use
bit_cast<int64_t>(GetFloatConstantValue(node)) == V8_INT64_C(0)

[martyn.capewell, 2016/05/04 09:47:47]

Done.

       return UseImmediate(node);
     }
     return UseRegister(node);
@@ -68,6 +70,19 @@ class Arm64OperandGenerator final : public OperandGenerator {
     return OpParameter<int64_t>(node);
   }
 
+  bool IsFloatConstant(Node* node) {
+    return (node->opcode() == IrOpcode::kFloat32Constant) ||
+           (node->opcode() == IrOpcode::kFloat64Constant);
+  }
+
+  double GetFloatConstantValue(Node* node) {
+    if (node->opcode() == IrOpcode::kFloat32Constant) {
+      return OpParameter<float>(node);
+    }
+    DCHECK(node->opcode() == IrOpcode::kFloat64Constant);

[Benedikt Meurer, 2016/05/03 17:33:20]

Nit: Use DCHECK_EQ(IrOpcode::kFloat64Constant, node->opcode())

[martyn.capewell, 2016/05/04 09:47:47]

Done.

+    return OpParameter<double>(node);
+  }
+
   bool CanBeImmediate(Node* node, ImmediateMode mode) {
     return IsIntegerConstant(node) &&
            CanBeImmediate(GetIntegerConstantValue(node), mode);
@@ -477,10 +492,12 @@ void InstructionSelector::VisitStore(Node* node) {
     }
     if (g.CanBeImmediate(index, immediate_mode)) {
       Emit(opcode | AddressingModeField::encode(kMode_MRI), g.NoOutput(),
-           g.UseRegister(base), g.UseImmediate(index), g.UseRegister(value));
+           g.UseRegister(base), g.UseImmediate(index),
+           g.UseRegisterOrImmediateZero(value));
     } else {
       Emit(opcode | AddressingModeField::encode(kMode_MRR), g.NoOutput(),
-           g.UseRegister(base), g.UseRegister(index), g.UseRegister(value));
+           g.UseRegister(base), g.UseRegister(index),
+           g.UseRegisterOrImmediateZero(value));
     }
   }
 }
@@ -559,7 +576,8 @@ void InstructionSelector::VisitCheckedStore(Node* node) {
       return;
   }
   Emit(opcode, g.NoOutput(), g.UseRegister(buffer), g.UseRegister(offset),
-       g.UseOperand(length, kArithmeticImm), g.UseRegister(value));
+       g.UseOperand(length, kArithmeticImm),
+       g.UseRegisterOrImmediateZero(value));
 }