http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24815
Oleg Endo <olegendo at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target|sh-elf |sh*-*-*
Last reconfirmed|2006-04-24 22:37:46 |2012-07-22
CC| |olegendo at gcc dot gnu.org
Depends on| |50749
--- Comment #5 from Oleg Endo <olegendo at gcc dot gnu.org> 2012-07-22 16:25:55
UTC ---
As of rev 189746 I was able to reproduce the problem with the following reduced
test case:
extern int tbl[1000];
void f (int* b, const int* a)
{
for (int i = 0; i < 998; i++)
b[i] = a[tbl[i]];
}
... compiled with '-O2 -m4-single -ml' (no loop unrolling):
mov.l .L6,r3 ! 66 movsi_ie/1 [length = 2]
mov #0,r7 ! 40 movsi_ie/3 [length = 2]
mov.w .L7,r2 ! 70 *movhi/1 [length = 2]
.align 2
.L3:
mov r7,r0 ! 77 movsi_ie/2 [length = 2]
mov.l @(r0,r3),r1 ! 46 movsi_ie/7 [length = 2]
dt r2 ! 71 dect [length = 2]
shll2 r1 ! 47 ashlsi3_std/3 [length = 2]
mov r1,r0 ! 78 movsi_ie/2 [length = 2]
mov.l @(r0,r5),r1 ! 49 movsi_ie/7 [length = 2]
mov r7,r0 ! 79 movsi_ie/2 [length = 2]
add #4,r7 ! 51 *addsi3_compact [length = 2]
bf/s .L3 ! 72 branch_false [length = 2]
mov.l r1,@(r0,r4) ! 50 movsi_ie/11 [length = 2]
rts
nop ! 83 *return_i [length = 4]
.align 1
.L7:
.short 998
.L8:
.align 2
.L6:
.long _tbl
... which would be better as:
mov.l .L6,r3
mov.w .L7,r2
.L3:
mov.l @r3+,r0
dt r2
shll2 r0
mov.l @(r0,r5),r1
mov.l r1,@r4
bf/s .L3
add #4,r4
rts
nop
With loop unrolling enabled it looks similar to the code in comment #2.
It seems that this issue also depends on the auto-inc-dec related PR 50749.
