Implemented the RoundUint64ToFloat64 TurboFan operator for x64 and arm64.

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 eab8fe323313579adbed0fb5f64cbaf0dd97d71b..803e4412ed5ca9189303c8aa8ef3be42b18c58c9 100644
--- a/src/compiler/x64/code-generator-x64.cc
+++ b/src/compiler/x64/code-generator-x64.cc
@@ -1032,6 +1032,14 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
         __ Cvtqsi2sd(i.OutputDoubleRegister(), i.InputOperand(0));
       }
       break;
+    case kSSEUint64ToFloat64:
+      if (instr->InputAt(0)->IsRegister()) {
+        __ movq(kScratchRegister, i.InputRegister(0));
+      } else {
+        __ movq(kScratchRegister, i.InputOperand(0));
+      }
+      __ Cvtqui2sd(i.OutputDoubleRegister(), kScratchRegister);
+      break;
     case kSSEUint32ToFloat64:
       if (instr->InputAt(0)->IsRegister()) {
         __ movl(kScratchRegister, i.InputRegister(0));