[turbofan] Implemented the TruncateFloat64ToUint64 TurboFan operator.

src/compiler/x64/code-generator-x64.cc

Index: src/compiler/x64/code-generator-x64.cc
diff --git a/src/compiler/x64/code-generator-x64.cc b/src/compiler/x64/code-generator-x64.cc
index 1c80ad85baa8fd6eb5eec196ea8e00fa17f47782..172cbb9c8debb92bc744da2743a96b4e2e3fdbb9 100644
--- a/src/compiler/x64/code-generator-x64.cc
+++ b/src/compiler/x64/code-generator-x64.cc
@@ -1027,6 +1027,42 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
         __ Cvttsd2siq(i.OutputRegister(), i.InputOperand(0));
       }
       break;
+    case kSSEFloat64ToUint64: {
+      // There does not exist a Float64ToUint64 instruction, so we have to use
+      // the Float64ToInt64 instruction.
+      if (instr->InputAt(0)->IsDoubleRegister()) {
+        __ Cvttsd2siq(i.OutputRegister(), i.InputDoubleRegister(0));
+      } else {
+        __ Cvttsd2siq(i.OutputRegister(), i.InputOperand(0));
+      }
+      // Check if the result of the Float64ToInt64 conversion is positive, we
+      // are already done.
+      __ testq(i.OutputRegister(), i.OutputRegister());
+      Label done;
+      __ j(positive, &done);
+      // The result of the first conversion was negative, which means that the
+      // input value was not within the positive int64 range. We substract 2^64

[titzer, 2015/11/19 19:41:10]

/substract/subtract/

+      // and convert it again to see if it is within the uint64 range.
+      __ Move(kScratchDoubleReg, -9223372036854775808.0);
+      if (instr->InputAt(0)->IsDoubleRegister()) {
+        __ addsd(kScratchDoubleReg, i.InputDoubleRegister(0));
+      } else {
+        __ addsd(kScratchDoubleReg, i.InputOperand(0));
+      }
+      __ Cvttsd2siq(i.OutputRegister(), kScratchDoubleReg);
+      __ testq(i.OutputRegister(), i.OutputRegister());
+      // The only possible negative value here is 0x80000000000000000, which is
+      // used on x64 to indicate an integer overflow.
+      __ j(negative, &done);
+      // The input value is within uint64 range and the second conversion worked
+      // successfully, but we still have to undo the substruction we did

[titzer, 2015/11/19 19:41:10]

s/substruction/subtraction

+      // earlier.
+      __ movq(kScratchRegister, Immediate(1));
+      __ shlq(kScratchRegister, Immediate(63));
+      __ orq(i.OutputRegister(), kScratchRegister);
+      __ bind(&done);
+      break;
+    }
     case kSSEInt32ToFloat64:
       if (instr->InputAt(0)->IsRegister()) {
         __ Cvtlsi2sd(i.OutputDoubleRegister(), i.InputRegister(0));