MIPS: Fix uninitialized upper word bits for Cvt_d_uw macro.

After Cvt_d_uw macro, upper 32 bits of the output remain
unitnitialized which caused flaky failures on some tests on
MIPS32R6

TEST=cctest/test-assembler-mips/MIPS13,mjsunit/asm/int32-umod
BUG=

Review URL: https://codereview.chromium.org/1537973002

Cr-Commit-Position: refs/heads/master@{#32983}

src/mips/macro-assembler-mips.cc

@@ -1270,6 +1270,7 @@ void MacroAssembler::Cvt_d_uw(FPURegister fd, Register rs,
   // In FP64Mode we do convertion from long.
   if (IsFp64Mode()) {
     mtc1(rs, scratch);
+    Mthc1(zero_reg, scratch);
     cvt_d_l(fd, scratch);
   } else {
     // Convert rs to a FP value in fd.

test/cctest/test-assembler-mips.cc

@@ -1819,48 +1819,46 @@ TEST(rint_s)  {
 
 
 TEST(Cvt_d_uw) {
-  if (IsMipsArchVariant(kMips32r2)) {
-    CcTest::InitializeVM();
-    Isolate* isolate = CcTest::i_isolate();
-    HandleScope scope(isolate);
-    MacroAssembler assm(isolate, NULL, 0,
-                        v8::internal::CodeObjectRequired::kYes);
+  CcTest::InitializeVM();
+  Isolate* isolate = CcTest::i_isolate();
+  HandleScope scope(isolate);
+  MacroAssembler assm(isolate, NULL, 0,
+                      v8::internal::CodeObjectRequired::kYes);
 
-    typedef struct test_struct {
-      unsigned input;
-      uint64_t output;
-    } TestStruct;
+  typedef struct test_struct {
+    unsigned input;
+    uint64_t output;
+  } TestStruct;
 
-    unsigned inputs[] = {
-      0x0, 0xffffffff, 0x80000000, 0x7fffffff
-    };
+  unsigned inputs[] = {
+    0x0, 0xffffffff, 0x80000000, 0x7fffffff
+  };
 
-    uint64_t outputs[] = {
-      0x0, 0x41efffffffe00000,
-      0x41e0000000000000, 0x41dfffffffc00000
-    };
+  uint64_t outputs[] = {
+    0x0, 0x41efffffffe00000,
+    0x41e0000000000000, 0x41dfffffffc00000
+  };
 
-    int kTableLength = sizeof(inputs)/sizeof(inputs[0]);
+  int kTableLength = sizeof(inputs)/sizeof(inputs[0]);
 
-    TestStruct test;
+  TestStruct test;
 
-    __ lw(t1, MemOperand(a0, offsetof(TestStruct, input)));
-    __ Cvt_d_uw(f4, t1, f6);
-    __ sdc1(f4, MemOperand(a0, offsetof(TestStruct, output)));
-    __ jr(ra);
-    __ nop();
+  __ lw(t1, MemOperand(a0, offsetof(TestStruct, input)));
+  __ Cvt_d_uw(f4, t1, f6);
+  __ sdc1(f4, MemOperand(a0, offsetof(TestStruct, output)));
+  __ jr(ra);
+  __ nop();
 
-    CodeDesc desc;
-    assm.GetCode(&desc);
-    Handle<Code> code = isolate->factory()->NewCode(
-        desc, Code::ComputeFlags(Code::STUB), Handle<Code>());
-    F3 f = FUNCTION_CAST<F3>(code->entry());
-    for (int i = 0; i < kTableLength; i++) {
-      test.input = inputs[i];
-      (CALL_GENERATED_CODE(isolate, f, &test, 0, 0, 0, 0));
-      // Check outputs
-      CHECK_EQ(test.output, outputs[i]);
-    }
+  CodeDesc desc;
+  assm.GetCode(&desc);
+  Handle<Code> code = isolate->factory()->NewCode(
+      desc, Code::ComputeFlags(Code::STUB), Handle<Code>());
+  F3 f = FUNCTION_CAST<F3>(code->entry());
+  for (int i = 0; i < kTableLength; i++) {
+    test.input = inputs[i];
+    (CALL_GENERATED_CODE(isolate, f, &test, 0, 0, 0, 0));
+    // Check outputs
+    CHECK_EQ(test.output, outputs[i]);
   }
 }