[Cbe-oss-dev] SPU-GCC optimzation problem

[Trevor_Smigiel at PlayStation.Sony.com]

Ulrich,

Yes, removing that change, and another in combine.c, are the correct
fix.  I've made those changes in the 3C repository.

Trevor

* Ulrich Weigand <Ulrich.Weigand at de.ibm.com> [2008-03-11 09:05]:
> Hello Trevor,
> 
> please see Machida-san's bug report below.  It looks like this is a 
> problem that came in with your big PS3/FSF backport merge to the 3C 
> repository (rev. 770).   Before that, spu_rlmaskqwbyte would use an 
> UNSPEC_SPU_ROTQBY unspec which never got optimized.  After that change, 
> the intrinsic is open-coded in terms of an LSHIFTRT rtx.
> 
> This would be perfectly fine normally, as long as SHIFT_COUNT_TRUNCATED is 
> not defined (which is isn't on spu).   However, there is special CELL 
> LOCAL code in simplify-rtx.c:simplify_binary_operation_1 which uses an 
> #ifdef SPU hack to *always* truncate shift counts anyway.
> 
> There is some comment around this CELL LOCAL section that seems to say 
> this is required to fix a bug in some test case.  I'm wondering whether 
> this statement is still correct after the rev. 770 changes to the back-end 
> ...   Reverting this CELL LOCAL change fixes the problem reported below. 
> Can you advise whether this is right thing to do?  Thanks!
> 
> 
> Machida-san, thanks for reporting the problem!
> 
> 
> Mit freundlichen Gruessen / Best Regards
> 
> Ulrich Weigand
> 
> -- 
>   Dr. Ulrich Weigand | Phone: +49-7031/16-3727
>   GNU compiler/toolchain for Linux on System z and Cell BE
>   IBM Deutschland Entwicklung GmbH
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> 
> 
> 
> "Hiroyuki Machida" <Hiroyuki.Mach at gmail.com> 
> Sent by: cbe-oss-dev-bounces+ulrich.weigand=de.ibm.com at ozlabs.org
> 03/11/08 10:10 AM
> Please respond to
> Hiroyuki.Mach at gmail.com
> 
> 
> To
> cbe-oss-dev at ozlabs.org
> cc
> 
> Subject
> [Cbe-oss-dev] SPU-GCC optimzation problem
> 
> 
> 
> 
> 
> 
> Hi,
> 
> I got a problem with SPU-GCC in IBM Cell SDK 3.0.
> I could not reproduce this with SPU-GCC in  older Cell
> SDK 2.1 or 2.0. I attached details, below.
> 
> 
> Hiroyuki.
> 
> ---
> 
> * Summary
> 
>   The spu-gcc generates incorrect code for spu_rlmaskqwbyte intrinsic
>   when:
> 
>   -- compiled with "-O1" or higher optimization level and
> 
>   -- the second argument is a constant (immediate) value and
> 
>   -- 1 <= (the second argument) mod 32 <= 16
> 
> * Version
> 
>   IBM Cell SDK 3.0 spu-gcc, spu-g++
> 
>   IBM Cell SDK 2.1 or earlier don't have this problem.
> 
> * Sample code
> 
> ---
> #include <spu_intrinsics.h>
> 
> vector unsigned int source = { 0x11111111, 0x22222222, 0x33333333,
> 0x44444444, };
> 
> int main(int argc, char **argv)
> {
>   vector unsigned int result;
> 
>   result = spu_rlmaskqwbyte(source, -17);
> 
>   /* all elements should be zero. */
>   printf("0x%08x 0x%08x 0x%08x 0x%08x, \n",
> spu_extract(result, 0),
> spu_extract(result, 1),
> spu_extract(result, 2),
> spu_extract(result, 3));
> 
>   return 0;
> }
> ---
> 
> * Additional information
> 
>   It seems that when optimization is enabled, the second argument is
>   normalized into -15 to 0.
> 
> ---
> main:
>         ila     $3,.LC0
>         hbrr    .L3,printf
>         lqr     $2,source
>         stqd    $lr,16($sp)
>         stqd    $sp,-32($sp)
>         ai      $sp,$sp,-32
>         nop     127
>         rotqmbyi        $7,$2,-1 # <==========
>         ori     $4,$7,0
>         rotqbyi $5,$7,(1*4+0)%16
>         rotqbyi $6,$7,(2*4+0)%16
>         rotqbyi $7,$7,(3*4+0)%16
>         nop     127
> .L3:
>         brsl    $lr,printf
>         ai      $sp,$sp,32
>         fsmbi   $3,0
>         lqd     $lr,16($sp)
>         bi      $lr
> ---
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