MIPS: Fixing floating point register clobbering

src/mips64/assembler-mips64.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 309 matching lines @@
 // Defined using #define instead of "static const Register&" because Clang
 // complains otherwise when a compilation unit that includes this header
 // doesn't use the variables.
 #define kRootRegister s6
 #define cp s7
 #define kLithiumScratchReg s3
 #define kLithiumScratchReg2 s4
 #define kLithiumScratchDouble f30
 #define kDoubleRegZero f28
 // Used on mips64r6 for compare operations.
-#define kDoubleCompareReg f31
+// We use the last non-callee saved odd register for N64 ABI
+#define kDoubleCompareReg f23
 
 // FPU (coprocessor 1) control registers.
 // Currently only FCSR (#31) is implemented.
 struct FPUControlRegister {
   bool is_valid() const { return code_ == kFCSRRegister; }
   bool is(FPUControlRegister creg) const { return code_ == creg.code_; }
   int code() const {
     DCHECK(is_valid());
     return code_;
   }
@@ skipping 1151 matching lines @@
 class EnsureSpace BASE_EMBEDDED {
  public:
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_ASSEMBLER_MIPS_H_