Fix x64 build (RBX is callee-saved, use R8 instead).

runtime/vm/assembler_x64_test.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/os.h"
 #include "vm/unit_test.h"
@@ skipping 671 matching lines @@
   EXPECT_EQ(0xffff, reinterpret_cast<MoveWordRex>(test->entry())());
 }
 
 
 ASSEMBLER_TEST_GENERATE(LongAddReg, assembler) {
   __ pushq(CallingConventions::kArg2Reg);
   __ pushq(CallingConventions::kArg1Reg);
   __ movl(RAX, Address(RSP, 0));  // left low.
   __ movl(RDX, Address(RSP, 4));  // left high.
   __ movl(RCX, Address(RSP, 8));  // right low.
-  __ movl(RBX, Address(RSP, 12));  // right high
+  __ movl(R8, Address(RSP, 12));  // right high
   __ addl(RAX, RCX);
-  __ adcl(RDX, RBX);
+  __ adcl(RDX, R8);
   // Result is in RAX/RDX.
   __ movl(Address(RSP, 0), RAX);  // result low.
   __ movl(Address(RSP, 4), RDX);  // result high.
   __ popq(RAX);
   __ popq(RDX);
   __ ret();
 }
 
 
 ASSEMBLER_TEST_RUN(LongAddReg, test) {
@@ skipping 37 matching lines @@
   EXPECT_EQ((a + b), res);
 }
 
 
 ASSEMBLER_TEST_GENERATE(LongSubReg, assembler) {
   __ pushq(CallingConventions::kArg2Reg);
   __ pushq(CallingConventions::kArg1Reg);
   __ movl(RAX, Address(RSP, 0));  // left low.
   __ movl(RDX, Address(RSP, 4));  // left high.
   __ movl(RCX, Address(RSP, 8));  // right low.
-  __ movl(RBX, Address(RSP, 12));  // right high
+  __ movl(R8, Address(RSP, 12));  // right high
   __ subl(RAX, RCX);
-  __ sbbl(RDX, RBX);
+  __ sbbl(RDX, R8);
   // Result is in RAX/RDX.
   __ movl(Address(RSP, 0), RAX);  // result low.
   __ movl(Address(RSP, 4), RDX);  // result high.
   __ popq(RAX);
   __ popq(RDX);
   __ ret();
 }
 
 
 ASSEMBLER_TEST_RUN(LongSubReg, test) {
@@ skipping 2430 matching lines @@
   int res = reinterpret_cast<ConditionalMovesNoOverflowCode>(
       test->entry())(0x7fffffffffffffff, 2);
   EXPECT_EQ(1, res);
   res = reinterpret_cast<ConditionalMovesNoOverflowCode>(test->entry())(1, 1);
   EXPECT_EQ(0, res);
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64