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

src/ia32/ic-ia32.cc

Index: src/ia32/ic-ia32.cc
===================================================================
--- src/ia32/ic-ia32.cc	(revision 3022)
+++ src/ia32/ic-ia32.cc	(working copy)
@@ -298,7 +298,6 @@
   __ 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);
@@ -427,11 +426,8 @@
     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));
@@ -458,7 +454,6 @@
   __ 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.