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* [Bug target/40416] New: unnecessary register spill
@ 2009-06-11 14:26 carrot at google dot com
2009-06-11 14:34 ` [Bug target/40416] " carrot at google dot com
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: carrot at google dot com @ 2009-06-11 14:26 UTC (permalink / raw)
To: gcc-bugs
Compile the attached source code with options -O2 -Os -mthumb -fpic, we can get
a unnecessary register spill.
--
Summary: unnecessary register spill
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
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=40416
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug target/40416] unnecessary register spill
2009-06-11 14:26 [Bug target/40416] New: unnecessary register spill carrot at google dot com
@ 2009-06-11 14:34 ` carrot at google dot com
2009-06-12 12:54 ` ramana at gcc dot gnu dot org
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: carrot at google dot com @ 2009-06-11 14:34 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from carrot at google dot com 2009-06-11 14:34 -------
Created an attachment (id=17983)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17983&action=view)
test case
The spilling is occurred around the first loop:
push {r4, r5, r6, r7, lr}
sub sp, sp, #12
.loc 1 5 0
str r2, [sp, #4] // A
.loc 1 6 0
add r6, r1, r2
mov r4, r0
.loc 1 8 0
b .L2
.L5:
.loc 1 10 0
mov r7, #0
ldrsh r5, [r4, r7]
.loc 1 12 0
cmp r2, r5
bge .L3
.loc 1 14 0
ldrb r7, [r1]
strb r7, [r1, r2]
.loc 1 15 0
strh r2, [r4]
.loc 1 16 0
lsl r1, r2, #1
sub r2, r5, r2
strh r2, [r1, r4]
.L6:
.loc 1 5 0
ldr r5, [sp, #4] // B
lsl r4, r5, #1
add r0, r0, r4
b .L4
.L3:
.loc 1 19 0
lsl r7, r5, #1
mov ip, r7
add r4, r4, ip
.loc 1 20 0
add r1, r1, r5
.loc 1 21 0
sub r2, r2, r5
.L2:
.loc 1 8 0
cmp r2, #0
bgt .L5
b .L6
.L4:
.loc 1 30 0
mov r1, #0
The spilling is occurred at instruction A and reload at instruction B.
The spilled value is x. The source code computes next_runs and next_alpha
before while loop and preserve them through the loop body. But the generated
code preserve next_alpha, original runs and original x through the loop body
and compute next_runs after the loop. This caused an extra usage of register
and results in a register spilling.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40416
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug target/40416] unnecessary register spill
2009-06-11 14:26 [Bug target/40416] New: unnecessary register spill carrot at google dot com
2009-06-11 14:34 ` [Bug target/40416] " carrot at google dot com
@ 2009-06-12 12:54 ` ramana at gcc dot gnu dot org
2009-06-15 2:27 ` carrot at google dot com
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: ramana at gcc dot gnu dot org @ 2009-06-12 12:54 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from ramana at gcc dot gnu dot org 2009-06-12 12:54 -------
(In reply to comment #1)
> Created an attachment (id=17983)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17983&action=view) [edit]
> test case
>
Your attachment didn't have #include <stdint.h> - Please try and supply
pre-processed input which is self contained . Adding a -I from a build
directory can be rather painful . Thanks -
> The spilling is occurred around the first loop:
>
> push {r4, r5, r6, r7, lr}
> sub sp, sp, #12
> .loc 1 5 0
> str r2, [sp, #4] // A
> .loc 1 6 0
> add r6, r1, r2
> mov r4, r0
> .loc 1 8 0
> b .L2
> .L5:
> .loc 1 10 0
> mov r7, #0
> ldrsh r5, [r4, r7]
> .loc 1 12 0
> cmp r2, r5
> bge .L3
> .loc 1 14 0
> ldrb r7, [r1]
> strb r7, [r1, r2]
> .loc 1 15 0
> strh r2, [r4]
> .loc 1 16 0
> lsl r1, r2, #1
> sub r2, r5, r2
> strh r2, [r1, r4]
> .L6:
> .loc 1 5 0
> ldr r5, [sp, #4] // B
> lsl r4, r5, #1
> add r0, r0, r4
> b .L4
> .L3:
> .loc 1 19 0
> lsl r7, r5, #1
> mov ip, r7
> add r4, r4, ip
> .loc 1 20 0
> add r1, r1, r5
> .loc 1 21 0
> sub r2, r2, r5
> .L2:
> .loc 1 8 0
> cmp r2, #0
> bgt .L5
> b .L6
> .L4:
> .loc 1 30 0
> mov r1, #0
>
>
> The spilling is occurred at instruction A and reload at instruction B.
>
> The spilled value is x. The source code computes next_runs and next_alpha
> before while loop and preserve them through the loop body. But the generated
> code preserve next_alpha, original runs and original x through the loop body
> and compute next_runs after the loop. This caused an extra usage of register
> and results in a register spilling.
>
Could you say what you'd like the code to be because I don't see an option but
to spill one of the values here. ?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40416
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug target/40416] unnecessary register spill
2009-06-11 14:26 [Bug target/40416] New: unnecessary register spill carrot at google dot com
2009-06-11 14:34 ` [Bug target/40416] " carrot at google dot com
2009-06-12 12:54 ` ramana at gcc dot gnu dot org
@ 2009-06-15 2:27 ` carrot at google dot com
2009-06-15 2:32 ` carrot at google dot com
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: carrot at google dot com @ 2009-06-15 2:27 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from carrot at google dot com 2009-06-15 02:26 -------
Created an attachment (id=17998)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17998&action=view)
preprocessed test case
A possible code sequence without spilling is:
push {r4, r5, r6, r7, lr}
add r6, r1, r2
mov r4, r0
lsl r7, r2, 1 // New
add r0, r0, r7 // New
.loc 1 8 0
b .L2
.L5:
.loc 1 10 0
mov r7, #0
ldrsh r5, [r4, r7]
.loc 1 12 0
cmp r2, r5
bge .L3
.loc 1 14 0
ldrb r7, [r1]
strb r7, [r1, r2]
.loc 1 15 0
strh r2, [r4]
.loc 1 16 0
lsl r1, r2, #1
sub r2, r5, r2
strh r2, [r1, r4]
.L6:
.loc 1 5 0
b .L4
.L3:
.loc 1 19 0
lsl r7, r5, #1
mov ip, r7
add r4, r4, ip
.loc 1 20 0
add r1, r1, r5
.loc 1 21 0
sub r2, r2, r5
.L2:
.loc 1 8 0
cmp r2, #0
bgt .L5
b .L6
.L4:
.loc 1 30 0
mov r1, #0
--
carrot at google dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
Attachment #17983|0 |1
is obsolete| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40416
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug target/40416] unnecessary register spill
2009-06-11 14:26 [Bug target/40416] New: unnecessary register spill carrot at google dot com
` (2 preceding siblings ...)
2009-06-15 2:27 ` carrot at google dot com
@ 2009-06-15 2:32 ` carrot at google dot com
2009-06-15 9:14 ` ramana at gcc dot gnu dot org
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: carrot at google dot com @ 2009-06-15 2:32 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from carrot at google dot com 2009-06-15 02:32 -------
In the source code, only two extra variables next_runs and next_alpha need to
be preserved through the while loop.
But in the gcc generated code, three variables are kept through the first loop.
They are next_alpha, original runs and original x. The expression (next_runs =
runs + x) is moved after the loop. This caused an extra var through the loop
and resulted in register spilling.
The expression move is occurred in tree-ssa-sink pass. Daniel Berlin has
confirmed it is a bug in this pass.
******** From Daniel **************
This looks like a bug, i think i know what causes it.
When I wrote this pass, i forgot to make this check:
/* It doesn't make sense to move to a dominator that post-dominates
frombb, because it means we've just moved it into a path that always
executes if frombb executes, instead of reducing the number of
executions . */
if (dominated_by_p (CDI_POST_DOMINATORS, frombb, commondom))
happen regardless of whether it is a single use statement or not.
So it will sink single use statements even if it's just moving them to
places that aren't executed less frequently.
Add that check (changing commondom to sinkbb) and it should stop moving it.
*********** End From Daniel ****************
I will send the patch later.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40416
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug target/40416] unnecessary register spill
2009-06-11 14:26 [Bug target/40416] New: unnecessary register spill carrot at google dot com
` (3 preceding siblings ...)
2009-06-15 2:32 ` carrot at google dot com
@ 2009-06-15 9:14 ` ramana at gcc dot gnu dot org
2009-06-22 16:32 ` steven at gcc dot gnu dot org
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: ramana at gcc dot gnu dot org @ 2009-06-15 9:14 UTC (permalink / raw)
To: gcc-bugs
--
ramana at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2009-06-15 09:14:05
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40416
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug target/40416] unnecessary register spill
2009-06-11 14:26 [Bug target/40416] New: unnecessary register spill carrot at google dot com
` (4 preceding siblings ...)
2009-06-15 9:14 ` ramana at gcc dot gnu dot org
@ 2009-06-22 16:32 ` steven at gcc dot gnu dot org
2009-06-30 7:42 ` carrot at google dot com
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: steven at gcc dot gnu dot org @ 2009-06-22 16:32 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from steven at gcc dot gnu dot org 2009-06-22 16:32 -------
Did that patch go in already?
--
steven at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
URL| |http://gcc.gnu.org/ml/gcc-
| |patches/2009-
| |06/msg01168.html
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40416
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug target/40416] unnecessary register spill
2009-06-11 14:26 [Bug target/40416] New: unnecessary register spill carrot at google dot com
` (5 preceding siblings ...)
2009-06-22 16:32 ` steven at gcc dot gnu dot org
@ 2009-06-30 7:42 ` carrot at google dot com
2009-06-30 8:19 ` steven at gcc dot gnu dot org
2009-06-30 8:21 ` steven at gcc dot gnu dot org
8 siblings, 0 replies; 10+ messages in thread
From: carrot at google dot com @ 2009-06-30 7:42 UTC (permalink / raw)
To: gcc-bugs
------- Comment #6 from carrot at google dot com 2009-06-30 07:42 -------
http://gcc.gnu.org/ml/gcc-cvs/2009-06/msg01067.html
--
carrot at google dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40416
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug target/40416] unnecessary register spill
2009-06-11 14:26 [Bug target/40416] New: unnecessary register spill carrot at google dot com
` (6 preceding siblings ...)
2009-06-30 7:42 ` carrot at google dot com
@ 2009-06-30 8:19 ` steven at gcc dot gnu dot org
2009-06-30 8:21 ` steven at gcc dot gnu dot org
8 siblings, 0 replies; 10+ messages in thread
From: steven at gcc dot gnu dot org @ 2009-06-30 8:19 UTC (permalink / raw)
To: gcc-bugs
--
steven at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |4.5.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40416
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug target/40416] unnecessary register spill
2009-06-11 14:26 [Bug target/40416] New: unnecessary register spill carrot at google dot com
` (7 preceding siblings ...)
2009-06-30 8:19 ` steven at gcc dot gnu dot org
@ 2009-06-30 8:21 ` steven at gcc dot gnu dot org
8 siblings, 0 replies; 10+ messages in thread
From: steven at gcc dot gnu dot org @ 2009-06-30 8:21 UTC (permalink / raw)
To: gcc-bugs
------- Comment #7 from steven at gcc dot gnu dot org 2009-06-30 08:21 -------
Please adjust the test case:
/* { dg-options "-O2 -Os -fdump-tree-sink-stats" } */
This makes no sense, -Os implies -O2. So it should be:
/* { dg-options "-Os -fdump-tree-sink-stats" } */
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40416
^ permalink raw reply [flat|nested] 10+ messages in thread
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2009-06-11 14:26 [Bug target/40416] New: unnecessary register spill carrot at google dot com
2009-06-11 14:34 ` [Bug target/40416] " carrot at google dot com
2009-06-12 12:54 ` ramana at gcc dot gnu dot org
2009-06-15 2:27 ` carrot at google dot com
2009-06-15 2:32 ` carrot at google dot com
2009-06-15 9:14 ` ramana at gcc dot gnu dot org
2009-06-22 16:32 ` steven at gcc dot gnu dot org
2009-06-30 7:42 ` carrot at google dot com
2009-06-30 8:19 ` steven at gcc dot gnu dot org
2009-06-30 8:21 ` steven at gcc dot gnu dot org
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