[LLVMdev] VFCmp failing when unordered or UnsafeFPMath on x86

Chris Lattner sabre at nondot.org
Fri Jun 13 17:40:20 PDT 2008

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?

Please provide a testcase.

> 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.

LLVM is intended to support other vector instruction sets, including  
SPU, Alpha, etc.  The commonality was that the MSB is set, and we  
would like to add support for vector shifting at some point.

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