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* [Bug middle-end/45098] New: Missed induction variable optimization
@ 2010-07-28 2:39 carrot at google dot com
2010-07-30 17:23 ` [Bug middle-end/45098] " davidxl at gcc dot gnu dot org
2010-08-02 7:55 ` ramana at gcc dot gnu dot org
0 siblings, 2 replies; 3+ messages in thread
From: carrot at google dot com @ 2010-07-28 2:39 UTC (permalink / raw)
To: gcc-bugs
Compile the following code with options -march=armv7-a -mthumb -Os
extern void foo(int*);
void tr(int array[], int n)
{
int i;
for (i=0; i<n; i++)
foo(&array[i]);
}
GCC 4.6 generates:
push {r4, r5, r6, lr}
mov r6, r1
mov r5, r0
movs r4, #0
b .L2
.L3:
mov r0, r5
adds r4, r4, #1
bl foo
adds r5, r5, #4
.L2:
cmp r4, r6
blt .L3
pop {r4, r5, r6, pc}
We can see that both r4 and r5 are loop induction variables, and r4 is used for
loop counter only. So we can transform it to
push {r4, r5, r6, lr}
mov r5, r0
add r6, r5, r1 << 2
b .L2
.L3:
mov r0, r5
bl foo
adds r5, r5, #4
.L2:
cmp r5, r6
blt .L3
pop {r4, r5, r6, pc}
This new code is shorter and faster than original result, it uses one less
register at the same time.
Both tree-ssa and rtl loop optimizations missed this optimization.
--
Summary: Missed induction variable optimization
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: carrot at google dot com
GCC build triplet: i686-linux
GCC host triplet: i686-linux
GCC target triplet: arm-eabi
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45098
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug middle-end/45098] Missed induction variable optimization
2010-07-28 2:39 [Bug middle-end/45098] New: Missed induction variable optimization carrot at google dot com
@ 2010-07-30 17:23 ` davidxl at gcc dot gnu dot org
2010-08-02 7:55 ` ramana at gcc dot gnu dot org
1 sibling, 0 replies; 3+ messages in thread
From: davidxl at gcc dot gnu dot org @ 2010-07-30 17:23 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from davidxl at gcc dot gnu dot org 2010-07-30 17:23 -------
Seems -Os specific -- also reproducible on x86. With -O2, the result is
expected.
David
--
davidxl at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |davidxl at gcc dot gnu dot
| |org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45098
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug middle-end/45098] Missed induction variable optimization
2010-07-28 2:39 [Bug middle-end/45098] New: Missed induction variable optimization carrot at google dot com
2010-07-30 17:23 ` [Bug middle-end/45098] " davidxl at gcc dot gnu dot org
@ 2010-08-02 7:55 ` ramana at gcc dot gnu dot org
1 sibling, 0 replies; 3+ messages in thread
From: ramana at gcc dot gnu dot org @ 2010-08-02 7:55 UTC (permalink / raw)
To: gcc-bugs
--
ramana at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Keywords| |missed-optimization
Last reconfirmed|0000-00-00 00:00:00 |2010-08-02 07:55:00
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45098
^ permalink raw reply [flat|nested] 3+ messages in thread
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2010-07-28 2:39 [Bug middle-end/45098] New: Missed induction variable optimization carrot at google dot com
2010-07-30 17:23 ` [Bug middle-end/45098] " davidxl at gcc dot gnu dot org
2010-08-02 7:55 ` ramana at gcc dot gnu dot org
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