Change clamping 0..255 instruction sequence for pixel array code

src/ia32/ic-ia32.cc

 // Copyright 2006-2008 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 280 matching lines @@
   __ cmp(FieldOperand(ecx, HeapObject::kMapOffset),
          Immediate(Factory::pixel_array_map()));
   __ j(not_equal, &slow);
   __ cmp(eax, FieldOperand(ecx, PixelArray::kLengthOffset));
   __ j(above_equal, &slow);
   __ mov(ecx, FieldOperand(ecx, PixelArray::kExternalPointerOffset));
   __ movzx_b(eax, Operand(ecx, eax, times_1, 0));
   __ shl(eax, kSmiTagSize);
   __ ret(0);
 
-
   // Slow case: Load name and receiver from stack and jump to runtime.
   __ bind(&slow);
   __ IncrementCounter(&Counters::keyed_load_generic_slow, 1);
   KeyedLoadIC::Generate(masm, ExternalReference(Runtime::kKeyedGetProperty));
 
   __ bind(&check_string);
   // The key is not a smi.
   // Is it a string?
   __ CmpObjectType(eax, FIRST_NONSTRING_TYPE, edx);
   __ j(above_equal, &slow);
@@ skipping 105 matching lines @@
   // Check that the value is a smi. If a conversion is needed call into the
   // runtime to convert and clamp.
   __ test(eax, Immediate(kSmiTagMask));
   __ j(not_zero, &slow);
   __ sar(ebx, kSmiTagSize);  // Untag the index.
   __ cmp(ebx, FieldOperand(ecx, PixelArray::kLengthOffset));
   __ j(above_equal, &slow);
   __ mov(edx, eax);  // Save the value.
   __ sar(eax, kSmiTagSize);  // Untag the value.
   {  // Clamp the value to [0..255].
     Label done, is_negative;

[Tobias Kaes, 2009/10/08 07:42:43]

is_negative isn't used anymore, is it?

[Søren Thygesen Gjesse, 2009/10/08 07:46:14]

Absolutely right, I will get rid of it.

     __ test(eax, Immediate(0xFFFFFF00));
     __ j(zero, &done);
-    __ j(negative, &is_negative);
-    __ mov(eax, Immediate(255));
-    __ jmp(&done);
-    __ bind(&is_negative);
-    __ xor_(eax, Operand(eax));  // Clear eax.
+    __ setcc(negative, eax);  // 1 if negative, 0 if positive.
+    __ dec_b(eax);  // 0 if negative, 255 if positive.
     __ bind(&done);
   }
   __ mov(ecx, FieldOperand(ecx, PixelArray::kExternalPointerOffset));
   __ mov_b(Operand(ecx, ebx, times_1, 0), eax);
   __ mov(eax, edx);  // Return the original value.
   __ ret(0);
 
   // Extra capacity case: Check if there is extra capacity to
   // perform the store and update the length. Used for adding one
   // element to the array by writing to array[array.length].
   __ bind(&extra);
   // eax: value
   // edx: JSArray
   // ecx: FixedArray
   // ebx: index (as a smi)
   // flags: compare (ebx, edx.length())
   __ j(not_equal, &slow, not_taken);  // do not leave holes in the array
   __ sar(ebx, kSmiTagSize);  // untag
   __ cmp(ebx, FieldOperand(ecx, Array::kLengthOffset));
   __ j(above_equal, &slow, not_taken);
   // Restore tag and increment.
   __ lea(ebx, Operand(ebx, times_2, 1 << kSmiTagSize));
   __ mov(FieldOperand(edx, JSArray::kLengthOffset), ebx);
   __ sub(Operand(ebx), Immediate(1 << kSmiTagSize));  // decrement ebx again
   __ jmp(&fast);
 
-
   // Array case: Get the length and the elements array from the JS
   // array. Check that the array is in fast mode; if it is the
   // length is always a smi.
   __ bind(&array);
   // eax: value
   // edx: JSArray
   // ebx: index (as a smi)
   __ mov(ecx, FieldOperand(edx, JSObject::kElementsOffset));
   __ cmp(FieldOperand(ecx, HeapObject::kMapOffset),
          Immediate(Factory::fixed_array_map()));
@@ skipping 561 matching lines @@
 
   // Do tail-call to runtime routine.
   __ TailCallRuntime(
       ExternalReference(IC_Utility(kSharedStoreIC_ExtendStorage)), 3, 1);
 }
 
 #undef __
 
 
 } }  // namespace v8::internal