Serious code size regression from 3.0.2 to now part two

[tm]

On Fri, 26 Jul 2002, Joern Rennecke wrote:

> tm wrote:
> > 
> > Okay, I've started using -fno-reorder-blocks on my testcase map_fog.i, and
> > the code size is still about 10% worse than 3.0.x.
> > 
> > I think I've tracked this down to really bad branches being generated by
> > gcc. Take a look at this code sequence:
> > 
> >  5124                   .L320:
> >  5125 2a02 4011                 cmp/pz  r0
> >  5126 2a04 8F0C                 bf/s    .L322
> >  5127 2a06 6813                 mov     r1,r8
> >  5128 2a08 9226                 mov.w   .L683,r2
> >  5129 2a0a 3027                 cmp/gt  r2,r0
> >  5130 2a0c 8F09                 bf/s    .L323
> >  5131 2a0e 6103                 mov     r0,r1
> >  5132 2a10 A007                 bra     .L323
> >  5133 2a12 6123                 mov     r2,r1
> >  5134 2a14 00090009             .align 5
> >  5134      00090009
> >  5134      00090009
> >  5135                   .L322:
> >  5136 2a20 E100                 mov     #0,r1
> >  5137                   .L323:
> >  5138 2a22 6013                 mov     r1,r0
> >  5139 2a24 4818                 shll8   r8
> > ..
> > 
> > This is really twisted branch logic.
> 
> It appears the code is geared towards the r0 < 0 case.  Assuming both
> r1 and r0 need to contain the result, optimized code would be:
> would be:
>  cmpz/pz r0
>  mov r1,r8
>  bf/s .L322
>  mov #0,r1
>  mov.w .L683,r2
>  mov r0,r1
>  cmp/gt r2,r0
>  bf L322
>  mov r2,r1
> L323:
>  mov r1,r0
> L322:

Yes. That's very similar to what 3.0.4 generates:

 4334                   .L719:
 4335 2004 4A11                 cmp/pz  r10
 4336 2006 8F05                 bf/s    .L323
 4337 2008 E100                 mov     #0,r1
 4338 200a 61A3                 mov     r10,r1
 4339 200c 31C7                 cmp/gt  r12,r1
 4340 200e 8F02                 bf/s    .L315
 4341 2010 6A13                 mov     r1,r10
 4342 2012 911C                 mov.w   .L648,r1
 4343                   .L323:
 4344 2014 6A13                 mov     r1,r10
 4345                   .L315:

I'll try to investigate some more to determine the culprit.

Toshi