[LLVMdev] IMPLICIT_DEF
Evan Cheng
evan.cheng at apple.com
Tue Apr 1 15:07:43 PDT 2008
IMPLICIT_DEF is a value defined by an 'undef' instruction:
http://llvm.org/docs/LangRef.html#undefvalues
It can come from source program or produced as result of optimization.
Evan
On Apr 1, 2008, at 2:58 PM, David Greene wrote:
> Can someone explain where things like IMPLICIT_DEF_FR64 come from?
> I believe something is noticing a use before def and inserting some
> kind of
> bogus code to compensate. The machine instructions look like this
> (x86):
>
> %reg1069<def> = IMPLICIT_DEF_FR64
> FsMOVLPDmr %reg0, 1, %reg0, 0, %reg1069
>
> This is no good -- it stores to zero.
>
> Thanks.
>
> -Dave
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