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* [Bug rtl-optimization/40327] New: Use less instructions to add some constants to register
@ 2009-06-03 7:39 carrot at google dot com
2009-06-03 10:36 ` [Bug target/40327] " steven at gcc dot gnu dot org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: carrot at google dot com @ 2009-06-03 7:39 UTC (permalink / raw)
To: gcc-bugs
Compiling this simple function in thumb mode:
int add_const(int x)
{
return x+400;
}
I got:
mov r1, #200
lsl r3, r1, #1
add r0, r0, r3
A better code sequence should be:
add r0, r0, 200
add r0, r0, 200
In order to apply this optimization, the constant should be less than 2 times
of the largest immediate value in the target ISA. So this optimization should
also useful to other architecture with limited immediate operand range.
It can also be applied to sub instruction.
--
Summary: Use less instructions to add some constants to register
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
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=40327
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/40327] Use less instructions to add some constants to register
2009-06-03 7:39 [Bug rtl-optimization/40327] New: Use less instructions to add some constants to register carrot at google dot com
@ 2009-06-03 10:36 ` steven at gcc dot gnu dot org
2009-06-03 10:58 ` steven at gcc dot gnu dot org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: steven at gcc dot gnu dot org @ 2009-06-03 10:36 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from steven at gcc dot gnu dot org 2009-06-03 10:36 -------
This code comes from the split2 (split insns after reload). So this is target
specific. It surprises me that non-legitimate constants are accepted before
reload on ARM (at least in thumb mode). It may be (and IMHO, probably is)
better to split the constant early, e.g. during expand. A REG_EQUAL note can
be used to remember the original value added.
--
steven at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Component|rtl-optimization |target
Ever Confirmed|0 |1
GCC build triplet|i686-linux |
GCC host triplet|i686-linux |
Last reconfirmed|0000-00-00 00:00:00 |2009-06-03 10:36:14
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40327
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/40327] Use less instructions to add some constants to register
2009-06-03 7:39 [Bug rtl-optimization/40327] New: Use less instructions to add some constants to register carrot at google dot com
2009-06-03 10:36 ` [Bug target/40327] " steven at gcc dot gnu dot org
@ 2009-06-03 10:58 ` steven at gcc dot gnu dot org
2009-06-09 22:06 ` rearnsha at gcc dot gnu dot org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: steven at gcc dot gnu dot org @ 2009-06-03 10:58 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from steven at gcc dot gnu dot org 2009-06-03 10:57 -------
FWIW it looks like the define_split at arm.c:5060 (of r147729) is triggered.
Richard E., is there a reason for lowering load-immediates so late in the
pipeline?
--
steven at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rearnsha at gcc dot gnu dot
| |org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40327
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/40327] Use less instructions to add some constants to register
2009-06-03 7:39 [Bug rtl-optimization/40327] New: Use less instructions to add some constants to register carrot at google dot com
2009-06-03 10:36 ` [Bug target/40327] " steven at gcc dot gnu dot org
2009-06-03 10:58 ` steven at gcc dot gnu dot org
@ 2009-06-09 22:06 ` rearnsha at gcc dot gnu dot org
2009-06-13 12:49 ` rearnsha at gcc dot gnu dot org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: rearnsha at gcc dot gnu dot org @ 2009-06-09 22:06 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from rearnsha at gcc dot gnu dot org 2009-06-09 22:06 -------
Working on a patch
--
rearnsha at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|unassigned at gcc dot gnu |rearnsha at gcc dot gnu dot
|dot org |org
Status|NEW |ASSIGNED
Last reconfirmed|2009-06-03 10:36:14 |2009-06-09 22:06:44
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40327
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/40327] Use less instructions to add some constants to register
2009-06-03 7:39 [Bug rtl-optimization/40327] New: Use less instructions to add some constants to register carrot at google dot com
` (2 preceding siblings ...)
2009-06-09 22:06 ` rearnsha at gcc dot gnu dot org
@ 2009-06-13 12:49 ` rearnsha at gcc dot gnu dot org
2009-06-13 13:04 ` rearnsha at gcc dot gnu dot org
2009-06-13 23:45 ` steven at gcc dot gnu dot org
5 siblings, 0 replies; 7+ messages in thread
From: rearnsha at gcc dot gnu dot org @ 2009-06-13 12:49 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from rearnsha at gcc dot gnu dot org 2009-06-13 12:49 -------
Subject: Bug 40327
Author: rearnsha
Date: Sat Jun 13 12:49:25 2009
New Revision: 148452
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=148452
Log:
PR target/40327
* arm/constraints.md (Pa, Pb): New constraints.
* arm/arm.md (thumb1_addsi3): Support more complex additions. Add a
split pattern to deal with them.
Modified:
trunk/gcc/ChangeLog
trunk/gcc/config/arm/arm.md
trunk/gcc/config/arm/constraints.md
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40327
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/40327] Use less instructions to add some constants to register
2009-06-03 7:39 [Bug rtl-optimization/40327] New: Use less instructions to add some constants to register carrot at google dot com
` (3 preceding siblings ...)
2009-06-13 12:49 ` rearnsha at gcc dot gnu dot org
@ 2009-06-13 13:04 ` rearnsha at gcc dot gnu dot org
2009-06-13 23:45 ` steven at gcc dot gnu dot org
5 siblings, 0 replies; 7+ messages in thread
From: rearnsha at gcc dot gnu dot org @ 2009-06-13 13:04 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from rearnsha at gcc dot gnu dot org 2009-06-13 13:04 -------
fixed
--
rearnsha at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution| |FIXED
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40327
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/40327] Use less instructions to add some constants to register
2009-06-03 7:39 [Bug rtl-optimization/40327] New: Use less instructions to add some constants to register carrot at google dot com
` (4 preceding siblings ...)
2009-06-13 13:04 ` rearnsha at gcc dot gnu dot org
@ 2009-06-13 23:45 ` steven at gcc dot gnu dot org
5 siblings, 0 replies; 7+ messages in thread
From: steven at gcc dot gnu dot org @ 2009-06-13 23:45 UTC (permalink / raw)
To: gcc-bugs
------- Comment #6 from steven at gcc dot gnu dot org 2009-06-13 23:45 -------
I would still like to know why these constants can't be lowered earlier.
Exposing the split-up insns may allow CSE to do a better job, etc.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40327
^ permalink raw reply [flat|nested] 7+ messages in thread
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2009-06-03 7:39 [Bug rtl-optimization/40327] New: Use less instructions to add some constants to register carrot at google dot com
2009-06-03 10:36 ` [Bug target/40327] " steven at gcc dot gnu dot org
2009-06-03 10:58 ` steven at gcc dot gnu dot org
2009-06-09 22:06 ` rearnsha at gcc dot gnu dot org
2009-06-13 12:49 ` rearnsha at gcc dot gnu dot org
2009-06-13 13:04 ` rearnsha at gcc dot gnu dot org
2009-06-13 23:45 ` steven at gcc dot gnu dot org
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