Improve ClampDoubleToUint8 on ia32/x64

src/x64/macro-assembler-x64.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 2850 matching lines @@
   testl(reg, Immediate(0xFFFFFF00));
   j(zero, &done, Label::kNear);
   setcc(negative, reg);  // 1 if negative, 0 if positive.
   decb(reg);  // 0 if negative, 255 if positive.
   bind(&done);
 }
 
 
 void MacroAssembler::ClampDoubleToUint8(XMMRegister input_reg,
                                         XMMRegister temp_xmm_reg,
-                                        Register result_reg,
-                                        Register temp_reg) {
+                                        Register result_reg) {
   Label done;
-  Set(result_reg, 0);
+  Label conv_failure;
   xorps(temp_xmm_reg, temp_xmm_reg);
-  ucomisd(input_reg, temp_xmm_reg);
-  j(below, &done, Label::kNear);
   cvtsd2si(result_reg, input_reg);
   testl(result_reg, Immediate(0xFFFFFF00));
   j(zero, &done, Label::kNear);
+  cmpl(result_reg, Immediate(0x80000000));
+  j(equal, &conv_failure, Label::kNear);
+  movl(result_reg, Immediate(0));
+  setcc(above, result_reg);
+  subl(result_reg, Immediate(1));
+  andl(result_reg, Immediate(255));
+  jmp(&done, Label::kNear);
+  bind(&conv_failure);
+  Set(result_reg, 0);
+  ucomisd(input_reg, temp_xmm_reg);
+  j(below, &done, Label::kNear);
   Set(result_reg, 255);
   bind(&done);
 }
 
 
 static double kUint32Bias =
     static_cast<double>(static_cast<uint32_t>(0xFFFFFFFF)) + 1;
 
 
 void MacroAssembler::LoadUint32(XMMRegister dst,
@@ skipping 1661 matching lines @@
 
   movq(rcx, FieldOperand(rbx, Map::kPrototypeOffset));
   cmpq(rcx, null_value);
   j(not_equal, &next);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64