[LLVMdev] Spilled variables using unaligned moves

[Evan Cheng]

This is on Windows / Cygwin? I think the dynamic stack pointer re- 
alignment doesn't happen until post- register allocation.

Assuming there aren't other instructions between the prologue and the  
first movups that mess up esp (there shouldn't), this is indeed a bug.  
Please file a bug and attach a bc file. Thanks.

Evan

On Jul 14, 2008, at 7:43 AM, Nicolas Capens wrote:

> Hi all,
>
> It looks like vector spills don’t use aligned moves even though the  
> stack is aligned. This seems like an optimization opportunity.
>
> The attached replacement of fibonacci.cpp generates x86 code like  
> this:
>
> 03A70010  push        ebp
> 03A70011  mov         ebp,esp
> 03A70013  and         esp,0FFFFFFF0h
> 03A70019  sub         esp,1A0h
> ...
> 03A7006C  movups      xmmword ptr [esp+180h],xmm7
> ...
> 03A70229  mulps       xmm1,xmmword ptr [esp+180h]
> ...
> 03A70682  movups      xmm0,xmmword ptr [esp+180h]
>
> Note how stores and loads use unaligned moves while it could use  
> aligned moves. It’s also interesting that the multiply does  
> correctly assume the stack to be 16-byte aligned.
>
> Is there something I’m doing wrong (again), or is this already known?
>
> Thanks a lot,
>
> Nicolas Capens
>
> <fibonacci.cpp>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20080714/4a62272b/attachment.html>