[turbofan] Changed TruncateFloat64ToInt64 to TryTruncateFloat64ToInt64.

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

Index: src/compiler/arm64/code-generator-arm64.cc
diff --git a/src/compiler/arm64/code-generator-arm64.cc b/src/compiler/arm64/code-generator-arm64.cc
index 750874cea812769bd3dcf437bdff4d9212b3bda3..86adc8b21c7c29470bcbb6a05105ad9958d2d8f5 100644
--- a/src/compiler/arm64/code-generator-arm64.cc
+++ b/src/compiler/arm64/code-generator-arm64.cc
@@ -33,6 +33,8 @@ class Arm64OperandConverter final : public InstructionOperandConverter {
     return InputDoubleRegister(index);
   }
 
+  size_t OutputCount() { return instr_->OutputCount(); }
+
   DoubleRegister OutputFloat32Register() { return OutputDoubleRegister().S(); }
 
   DoubleRegister OutputFloat64Register() { return OutputDoubleRegister(); }
@@ -1037,7 +1039,23 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       __ Fcvtzs(i.OutputRegister64(), i.InputFloat32Register(0));
       break;
     case kArm64Float64ToInt64:
-      __ Fcvtzs(i.OutputRegister64(), i.InputDoubleRegister(0));
+      __ Fcvtzs(i.OutputRegister(0), i.InputDoubleRegister(0));
+      if (i.OutputCount() > 1) {
+        UseScratchRegisterScope scope(masm());
+        Label overflow;
+        Label done;
+        __ Fcmp(i.InputDoubleRegister(0), i.InputDoubleRegister(0));
+        __ B(ne, &overflow);
+        __ Cmp(i.OutputRegister(0), i.InputInt64(1));

[Rodolph Perfetta (ARM), 2015/12/04 16:15:45]

Have a look at MacroAssembler::TryConvertDoubleToInt64. It detects overflow and
underflow by comparing to 1 and -1 and checking for overflow. The benefit being
1 and -1 can be encoded in the cmp instructions while INT64_[MIN|MAX] cannot.
the code there also use conditional cmp to avoid some branches. fcmp also has a
coditional variant so all the cmp can be chained without branches.

[ahaas, 2015/12/07 11:00:34]

Done.

+        __ B(eq, &overflow);
+        __ Cmp(i.OutputRegister(0), i.InputInt64(2));
+        __ B(eq, &overflow);
+        __ Mov(i.OutputRegister(1), 1);

[Rodolph Perfetta (ARM), 2015/12/04 16:15:45]

using cset will give you more compact code.

[ahaas, 2015/12/07 11:00:34]

Done.

+        __ B(&done);
+        __ Bind(&overflow);
+        __ Mov(i.OutputRegister(1), 0);
+        __ Bind(&done);
+      }
       break;
     case kArm64Float32ToUint64:
       __ Fcvtzu(i.OutputRegister64(), i.InputFloat32Register(0));