[LLVMdev] VFCmp failing when unordered or UnsafeFPMath on x86

Nicolas Capens nicolas at capens.net
Mon Jun 16 02:27:30 PDT 2008

Hi Evan,


No, I haven't filed a bug. I'd first like someone to confirm this behavior.
Anyway, I'll post some test code in a minute.


Can I contact Nate directly about the definition of VFCmp?






From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
Behalf Of Evan Cheng
Sent: Saturday, 14 June, 2008 01:04
To: LLVM Developers Mailing List
Cc: Nate Begeman
Subject: Re: [LLVMdev] VFCmp failing when unordered or UnsafeFPMath on x86



On Jun 13, 2008, at 12:27 AM, Nicolas Capens wrote:

Hi all,


When trying to generate a VFCmp instruction when UnsafeFPMath is set to true
I get an assert "Unexpected CondCode" on my x86 system. This also happens
with UnsafeFPMath set to false and using an unordered compare. Could someone
look into this?


Have you filed a bug?


While I'm at it, is there any reason why only the most significant bit of
the return value of VFCmp is defined (according to the documentation)? Both
AltiVec and SSE set the components of the result to either all 1's or all
0's. Having only the most significant bit doesn't seem useful to me at all,
and (arithmetic) shifting vectors to replicate the bit isn't supported.


Nate can probably explain this better than anyone.






Nicolas Capens

LLVM Developers mailing list
LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu


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