Avoid redundant smi check for Math.abs

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
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@@ skipping 3439 matching lines @@
 
   ASSERT(instr->value()->Equals(instr->result()));
   Representation r = instr->hydrogen()->value()->representation();
 
   if (r.IsDouble()) {
     XMMRegister scratch = xmm0;
     XMMRegister input_reg = ToDoubleRegister(instr->value());
     __ xorps(scratch, scratch);
     __ subsd(scratch, input_reg);
     __ andpd(input_reg, scratch);
-  } else if (r.IsInteger32()) {
+  } else if (r.IsInteger32() || r.IsSmi()) {

[Jakob Kummerow, 2013/07/31 12:27:27]

This code is wrong. EmitIntegerMathAbs() uses testl/negl, which don't handle
Smis correctly. Repro case:

var a = [-1, -2];
function foo() {
  return Math.abs(a[0]);
}
print(foo());
print(foo());
%OptimizeFunctionOnNextCall(foo);
print(foo());

     EmitIntegerMathAbs(instr);
   } else {  // Tagged case.
     DeferredMathAbsTaggedHeapNumber* deferred =
         new(zone()) DeferredMathAbsTaggedHeapNumber(this, instr);
     Register input_reg = ToRegister(instr->value());
     // Smi check.
     __ JumpIfNotSmi(input_reg, deferred->entry());
     __ SmiToInteger32(input_reg, input_reg);
     EmitIntegerMathAbs(instr);
     __ Integer32ToSmi(input_reg, input_reg);
@@ skipping 2103 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64