Refine a bit ClampXToUint8

src/ia32/macro-assembler-ia32.cc

 // Copyright 2012 the V8 project authors. 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.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 202 matching lines @@
                                         XMMRegister scratch_reg,
                                         Register result_reg) {
   Label done;
   Label conv_failure;
   xorps(scratch_reg, scratch_reg);
   cvtsd2si(result_reg, input_reg);
   test(result_reg, Immediate(0xFFFFFF00));
   j(zero, &done, Label::kNear);
   cmp(result_reg, Immediate(0x1));
   j(overflow, &conv_failure, Label::kNear);
-  mov(result_reg, Immediate(0));
-  setcc(sign, result_reg);
-  sub(result_reg, Immediate(1));
-  and_(result_reg, Immediate(255));
+  sar(result_reg, 31);
+  not_(result_reg);  // No zero extension seems to be safe here.
   jmp(&done, Label::kNear);
   bind(&conv_failure);
-  Move(result_reg, Immediate(0));
+  sar(result_reg, 31);
   ucomisd(input_reg, scratch_reg);
-  j(below, &done, Label::kNear);
-  Move(result_reg, Immediate(255));
+  j(above_equal, &done, Label::kNear);
+  Set(result_reg, Immediate(0));
   bind(&done);
 }
 
 
 void MacroAssembler::ClampUint8(Register reg) {
   Label done;
   test(reg, Immediate(0xFFFFFF00));
   j(zero, &done, Label::kNear);
-  setcc(negative, reg);  // 1 if negative, 0 if positive.
-  dec_b(reg);  // 0 if negative, 255 if positive.
+  sar(reg, 31);
+  not_(reg);  // No zero extension seems to be safe here.
   bind(&done);
 }
 
 
 void MacroAssembler::SlowTruncateToI(Register result_reg,
                                      Register input_reg,
                                      int offset) {
   DoubleToIStub stub(input_reg, result_reg, offset, true);
   call(stub.GetCode(isolate()), RelocInfo::CODE_TARGET);
 }
@@ skipping 3393 matching lines @@
   if (ms.shift() > 0) sar(edx, ms.shift());
   mov(eax, dividend);
   shr(eax, 31);
   add(edx, eax);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32