[LLVMdev] Shuffle regression

[Nicolas Capens]

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

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