MIPS: Fix Subu and add optimization

src/mips/macro-assembler-mips.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <limits.h>  // For LONG_MIN, LONG_MAX.
 
 #if V8_TARGET_ARCH_MIPS
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
@@ skipping 546 matching lines @@
       addu(rd, rs, at);
     }
   }
 }
 
 
 void MacroAssembler::Subu(Register rd, Register rs, const Operand& rt) {
   if (rt.is_reg()) {
     subu(rd, rs, rt.rm());
   } else {
-    if (is_int16(rt.imm32_) && !MustUseReg(rt.rmode_)) {
+    if (is_int16(-rt.imm32_) && !MustUseReg(rt.rmode_)) {
       addiu(rd, rs, -rt.imm32_);  // No subiu instr, use addiu(x, y, -imm).
+    } else if (!(-rt.imm32_ & kHiMask) && !MustUseReg(rt.rmode_)) {  // Use load
+      // -imm and addu for cases where loading -imm generates one instruction.
+      DCHECK(!rs.is(at));
+      li(at, -rt.imm32_);
+      addu(rd, rs, at);
     } else {
       // li handles the relocation.
       DCHECK(!rs.is(at));
       li(at, rt);
       subu(rd, rs, at);
     }
   }
 }
 
 
@@ skipping 6051 matching lines @@
   if (mag.shift > 0) sra(result, result, mag.shift);
   srl(at, dividend, 31);
   Addu(result, result, Operand(at));
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS