RE: Tree-SSA and POST_INC address mode inompatible in GCC4?

["Bingfeng Mei" <bmei@broadcom.com>]

Yes, that is the better way to generate code than using POST_INC since
it eliminates unnecessary dependency. Which version used to do this?
Where should it be done? I am thinking one of those copy propagation
passes. Am I right?

Cheers,
Bingfeng

-----Original Message-----
From: gcc-owner@gcc.gnu.org [mailto:gcc-owner@gcc.gnu.org] On Behalf Of
Zdenek Dvorak
Sent: 03 November 2007 15:27
To: Kenneth Zadeck
Cc: gcc@gcc.gnu.org
Subject: Re: Tree-SSA and POST_INC address mode inompatible in GCC4?

Hi,

> >> I believe that this is something new and is most likely fallout
from
> >> diego's reworking of the tree to rtl converter.
> >>
> >> To fix this will require a round of copy propagation, most likely
in
> >> concert with some induction variable detection, since the most
> >> profitable place for this will be in loops.  
> >>
> >> I wonder if any of this effects the rtl level induction variable
> >> discovery?
> >>     
> >
> > it should not (iv analysis is able to deal with this kind of ivs).
> >
> does the iv analysis canonize them in a way that we should perhaps
> consider moving the auto-inc detection after the iv analysis?

no, iv analysis does not change the program; also, since the code in
this particular example is not in any loop, iv analysis is somewhat
irrelevant for it.

Btw.  I would have actually expected this code to be folded to

 *a_3(D) = D.1543_2;
  a_4 = a_3(D) + 1;
  b_5 = b_1(D) + 1;
  D.1543_6 = *b_5;
  *a_4 = D.1543_6;
  a_7 = a_3 + 2;
  b_8 = b_1 + 2;
  D.1543_9 = *b_8;
  *a_7 = D.1543_9;
  a_10 = a_3 + 3;
  b_11 = b_1 + 3;
  D.1543_12 = *b_11;
  *a_10 = D.1543_12;
  a_13 = a_3 + 4;
  b_14 = b_1 + 4;
  D.1543_15 = *b_14;
  *a_13 = D.1543_15;

etc.; I am fairly sure we used to do this.

Zdenek