X64/Win64: Fix bug in returning ObjectPair.

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index d36af8c794baff92b507bbcb3cfbb4e9c33a5eaf..a4fd5928e92eee1811069b67014764389f18be2c 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -6862,6 +6862,15 @@ void CEntryStub::GenerateCore(MacroAssembler* masm,
   // Check for failure result.
   Label failure_returned;
   ASSERT(((kFailureTag + 1) & kFailureTagMask) == 0);
+#ifdef _WIN64
+  // If return value is on the stack, pop it to registers.
+  if (result_size_ > 1) {
+    ASSERT_EQ(2, result_size_);
+    // Position above 4 argument mirrors and arguments object.
+    __ movq(rax, Operand(rsp, 6 * kPointerSize));
+    __ movq(rdx, Operand(rsp, 7 * kPointerSize));
+  }
+#endif
   __ lea(rcx, Operand(rax, 1));
   // Lower 2 bits of rcx are 0 iff rax has failure tag.
   __ testl(rcx, Immediate(kFailureTagMask));