------- Comment #1 from steven at gcc dot gnu dot org 2010-01-04 18:53 -------
>From the tree optimizers we go to expand with the following code (from
PR42612.c.139t.optimized):
;; Function func (func)
func (char * p)
{
<bb 2>:
*p_1(D) = 0;
p_2 = p_1(D) + 1;
*p_2 = 0;
p_3 = p_2 + 1;
*p_3 = 0;
p_4 = p_3 + 1;
return p_4;
}
The code remains in this form until combine, which changes the code as follows
(left is PR42612.c.174r.dce, right is PR42612.c.175r.combine, dumped with
-fdump-rtl-all-slim):
4 NOTE_INSN_BASIC_BLOCK 4 NOTE_INSN_BASIC_BLOCK
2 r137:SI=r0:SI 2 r137:SI=r0:SI
REG_DEAD: r0:SI REG_DEAD: r0:SI
3 NOTE_INSN_FUNCTION_BEG 3 NOTE_INSN_FUNCTION_BEG
6 r138:SI=0x0 6 r138:SI=0x0
28 r133:SI=r137:SI 28 r133:SI=r137:SI
8 [r133:SI++]=r138:SI#0 8 [r133:SI++]=r138:SI#0
REG_INC: r133:SI REG_INC: r133:SI
REG_EQUAL: 0x0 REG_EQUAL: 0x0
12 [r137:SI+0x1]=r138:SI#0 12 [r137:SI+0x1]=r138:SI#0
REG_DEAD: r137:SI REG_DEAD: r137:SI
REG_EQUAL: 0x0 REG_EQUAL: 0x0
13 r134:SI=r133:SI+0x1 | 13 NOTE_INSN_DELETED
16 [r133:SI+0x1]=r138:SI#0 16 [r133:SI+0x1]=r138:SI#0
REG_DEAD: r138:SI REG_DEAD: r138:SI
REG_DEAD: r133:SI <
REG_EQUAL: 0x0 REG_EQUAL: 0x0
17 r144:SI=r134:SI+0x1 | 17 NOTE_INSN_DELETED
REG_DEAD: r134:SI | 22 r0:SI=r133:SI+0x2
22 r0:SI=r144:SI | REG_DEAD: r133:SI
REG_DEAD: r144:SI <
25 use r0:SI 25 use r0:SI
Paolo, you know combine best. Is there a way, you think, to teach combine about
post-increment addressing?
--
steven at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bonzini at gnu dot org
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2010-01-04 18:53:12
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42612
