Implemented the RoundInt64ToFloat32 TurboFan operator for x64, arm64, and mips64.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 5b0b9a04146904b787a5144d813922963448949d..c50c7ec126bf18e28f928a3e13203f7493ba037f 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -851,6 +851,30 @@ void MacroAssembler::Cvtlsi2sd(XMMRegister dst, const Operand& src) {
 }
 
 
+void MacroAssembler::Cvtqsi2ss(XMMRegister dst, Register src) {
+  if (CpuFeatures::IsSupported(AVX)) {
+    CpuFeatureScope scope(this, AVX);
+    vxorps(dst, dst, dst);
+    vcvtqsi2ss(dst, dst, src);
+  } else {
+    xorps(dst, dst);
+    cvtqsi2ss(dst, src);
+  }
+}
+
+
+void MacroAssembler::Cvtqsi2ss(XMMRegister dst, const Operand& src) {
+  if (CpuFeatures::IsSupported(AVX)) {
+    CpuFeatureScope scope(this, AVX);
+    vxorps(dst, dst, dst);
+    vcvtqsi2ss(dst, dst, src);
+  } else {
+    xorps(dst, dst);
+    cvtqsi2ss(dst, src);
+  }
+}
+
+
 void MacroAssembler::Cvtqsi2sd(XMMRegister dst, Register src) {
   if (CpuFeatures::IsSupported(AVX)) {
     CpuFeatureScope scope(this, AVX);