[LLVMdev] Shuffle regression

[Nicolas Capens]

52740 indeed fixes it. Thank you!

 

  _____  

From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
Behalf Of Evan Cheng
Sent: Saturday, 12 July, 2008 4:28
To: LLVM Developers Mailing List
Subject: Re: [LLVMdev] Shuffle regression

 

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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