[ia32/x64] Smaller instruction to check NaN

src/ia32/macro-assembler-ia32.cc

Index: src/ia32/macro-assembler-ia32.cc
diff --git a/src/ia32/macro-assembler-ia32.cc b/src/ia32/macro-assembler-ia32.cc
index eef2eddc82ef5f21ed5c0e0ca7f495a12fd59c91..2a9db06e07090190629d95db01cb0025e4ce7659 100644
--- a/src/ia32/macro-assembler-ia32.cc
+++ b/src/ia32/macro-assembler-ia32.cc
@@ -214,22 +214,20 @@ void MacroAssembler::ClampDoubleToUint8(XMMRegister input_reg,
                                         Register result_reg) {
   Label done;
   Label conv_failure;
-  pxor(scratch_reg, scratch_reg);
+  xorps(scratch_reg, scratch_reg);
   cvtsd2si(result_reg, input_reg);
   test(result_reg, Immediate(0xFFFFFF00));
   j(zero, &done, Label::kNear);
-  cmp(result_reg, Immediate(0x80000000));
-  j(equal, &conv_failure, Label::kNear);
-  mov(result_reg, Immediate(0));
-  setcc(above, result_reg);
-  sub(result_reg, Immediate(1));
-  and_(result_reg, Immediate(255));
+  cmp(result_reg, Immediate(0x1));
+  j(overflow, &conv_failure, Label::kNear);
+  sar(result_reg, 31);
+  not_(result_reg);  // safe not to zero extension

[Jakob Kummerow, 2014/03/19 12:00:30]

This comment doesn't make any sense, unless the reader knows that in one of the
places where you're putting it there used to be a movzx_b instruction.
Also, comments should be complete sentences with proper grammar, capitalization
and punctuation.

   jmp(&done, Label::kNear);
   bind(&conv_failure);
-  Set(result_reg, Immediate(0));
+  sar(result_reg, 31);
   ucomisd(input_reg, scratch_reg);
-  j(below, &done, Label::kNear);
-  Set(result_reg, Immediate(255));
+  j(above_equal, &done, Label::kNear);
+  Set(result_reg, Immediate(0));
   bind(&done);
 }
 
@@ -238,8 +236,8 @@ 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);  // safe not to zero extension
   bind(&done);
 }
 
@@ -256,8 +254,8 @@ void MacroAssembler::TruncateDoubleToI(Register result_reg,
                                        XMMRegister input_reg) {
   Label done;
   cvttsd2si(result_reg, Operand(input_reg));
-  cmp(result_reg, 0x80000000u);
-  j(not_equal, &done, Label::kNear);
+  cmp(result_reg, 0x1);
+  j(no_overflow, &done, Label::kNear);
 
   sub(esp, Immediate(kDoubleSize));
   movsd(MemOperand(esp, 0), input_reg);
@@ -374,8 +372,8 @@ void MacroAssembler::TruncateHeapNumberToI(Register result_reg,
     CpuFeatureScope scope(this, SSE2);
     movsd(xmm0, FieldOperand(input_reg, HeapNumber::kValueOffset));
     cvttsd2si(result_reg, Operand(xmm0));
-    cmp(result_reg, 0x80000000u);
-    j(not_equal, &done, Label::kNear);
+    cmp(result_reg, 0x1);
+    j(no_overflow, &done, Label::kNear);
     // Check if the input was 0x8000000 (kMinInt).
     // If no, then we got an overflow and we deoptimize.
     ExternalReference min_int = ExternalReference::address_of_min_int();