[LLVMdev] Shuffle regression

[Evan Cheng]

I have fixed a related bug: 52740. Can you check if that fixes this  
problem?

Evan

On Jul 11, 2008, at 6:43 PM, Nicolas Capens wrote:

> Hi all,
>
> I think I found a regression in the shuffle instruction. I’ve  
> attached a replacement of fibonacci.cpp to reproduce the issue. It  
> runs fine on release 2.3 but revision 52648 fails, and I suspect  
> that the issue is still present.
>
> 2.3 generates the following x86 code:
>
> 03A10010  push        ebp
> 03A10011  mov         ebp,esp
> 03A10013  and         esp,0FFFFFFF0h
> 03A10019  movups      xmm0,xmmword ptr ds:[141D280h]
> 03A10020  xorps       xmm1,xmm1
> 03A10023  movaps      xmm2,xmm0
> 03A10026  shufps      xmm2,xmm1,32h
> 03A1002A  movaps      xmm1,xmm0
> 03A1002D  shufps      xmm1,xmm2,84h
> 03A10031  shufps      xmm0,xmm1,23h
> 03A10035  shufps      xmm1,xmm1,40h
> 03A10039  shufps      xmm1,xmm0,2Eh
> 03A1003D  movups      xmmword ptr ds:[14262C0h],xmm1
> 03A10044  mov         esp,ebp
> 03A10046  pop         ebp
> 03A10047  ret
>
> While 52648 generates this:
>
> 03C60010  push        ebp
> 03C60011  mov         ebp,esp
> 03C60013  and         esp,0FFFFFFF0h
> 03C60019  movups      xmm0,xmmword ptr ds:[148E280h]
> 03C60020  xorps       xmm1,xmm1
> 03C60023  movaps      xmm2,xmm0
> 03C60026  shufps      xmm2,xmm1,32h
> 03C6002A  movaps      xmm1,xmm0
> 03C6002D  shufps      xmm1,xmm2,84h
> 03C60031  shufps      xmm1,xmm1,40h
> 03C60035  psrldq      xmm0,0Ch
> 03C6003A  shufps      xmm1,xmm0,2Eh
> 03C6003E  movups      xmmword ptr ds:[148E280h],xmm1
> 03C60045  mov         esp,ebp
> 03C60047  pop         ebp
> 03C60048  ret
>
> As I’m not using any optimization passes in this one I suspect that  
> the issue is somewhere in instruction selection. Note the  
> questionable use of the psrldq instruction.
>
> If anyone could have a look at this that would be great. I’ll try to  
> narrow down the change that caused this regression…
>
> Cheers,
>
> Nicolas Capens
> <fibonacci.cpp>
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