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* [Bug middle-end/20517] New: bit shift/mask optimization potential
@ 2005-03-17 13:17 Thomas dot Koenig at online dot de
2005-03-17 13:34 ` [Bug middle-end/20517] " Thomas dot Koenig at online dot de
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Thomas dot Koenig at online dot de @ 2005-03-17 13:17 UTC (permalink / raw)
To: gcc-bugs
$ cat shift.c
#include <stdio.h>
#define OFFSET 4
#define MASK 0xf0
int main()
{
unsigned int f,g;
scanf("%u",&f);
if ((f & MASK) >> OFFSET == 1) {
printf("success\n");
}
return 0;
}
$ gcc -S -O2 -fdump-tree-optimized shift.c
$ tail -20 shift.c.t66.optimized
unsigned int g;
unsigned int f;
int D.1807;
unsigned int D.1806;
unsigned int D.1805;
unsigned int f.10;
<bb 0>:
scanf (&"%u"[0], &f);
if ((f & 240) >> 4 == 1) goto <L0>; else goto <L1>;
<L0>:;
printf (&"success\n"[0]);
<L1>:;
return 0;
}
$ gcc -v
Using built-in specs.
Target: ia64-unknown-linux-gnu
Configured with: ../gcc-4.1-20050306/configure --prefix=/home/zfkts
--enable-languages=c,f95 --disable-optimization
Thread model: posix
gcc version 4.1.0 20050306 (experimental)
The expression (f & 0xf0) >> 4 == 1 could be optimized
to f & 0xf == 1 << 4.
Code like that occurs in the libgfortan library.
--
Summary: bit shift/mask optimization potential
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: Thomas dot Koenig at online dot de
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20517
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/20517] bit shift/mask optimization potential
2005-03-17 13:17 [Bug middle-end/20517] New: bit shift/mask optimization potential Thomas dot Koenig at online dot de
@ 2005-03-17 13:34 ` Thomas dot Koenig at online dot de
2005-03-17 17:21 ` [Bug tree-optimization/20517] " pinskia at gcc dot gnu dot org
2005-07-23 21:07 ` phython at gcc dot gnu dot org
2 siblings, 0 replies; 4+ messages in thread
From: Thomas dot Koenig at online dot de @ 2005-03-17 13:34 UTC (permalink / raw)
To: gcc-bugs
--
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20517
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/20517] bit shift/mask optimization potential
2005-03-17 13:17 [Bug middle-end/20517] New: bit shift/mask optimization potential Thomas dot Koenig at online dot de
2005-03-17 13:34 ` [Bug middle-end/20517] " Thomas dot Koenig at online dot de
@ 2005-03-17 17:21 ` pinskia at gcc dot gnu dot org
2005-07-23 21:07 ` phython at gcc dot gnu dot org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-03-17 17:21 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-03-17 17:21 -------
Confirmed, but this is already done on the RTL level. So the assembler looks same for what you
recomend and what is produced already.
--
What |Removed |Added
----------------------------------------------------------------------------
OtherBugsDependingO| |19986
nThis| |
Severity|normal |enhancement
Status|UNCONFIRMED |NEW
Component|middle-end |tree-optimization
Ever Confirmed| |1
Keywords| |TREE
Last reconfirmed|0000-00-00 00:00:00 |2005-03-17 17:21:20
date| |
Version|unknown |4.1.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20517
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/20517] bit shift/mask optimization potential
2005-03-17 13:17 [Bug middle-end/20517] New: bit shift/mask optimization potential Thomas dot Koenig at online dot de
2005-03-17 13:34 ` [Bug middle-end/20517] " Thomas dot Koenig at online dot de
2005-03-17 17:21 ` [Bug tree-optimization/20517] " pinskia at gcc dot gnu dot org
@ 2005-07-23 21:07 ` phython at gcc dot gnu dot org
2 siblings, 0 replies; 4+ messages in thread
From: phython at gcc dot gnu dot org @ 2005-07-23 21:07 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From phython at gcc dot gnu dot org 2005-07-23 21:05 -------
The condition around fold-const:9302 can be generalized to deal with this case.
--
What |Removed |Added
----------------------------------------------------------------------------
CC| |phython at gcc dot gnu dot
| |org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20517
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2005-07-23 21:05 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2005-03-17 13:17 [Bug middle-end/20517] New: bit shift/mask optimization potential Thomas dot Koenig at online dot de
2005-03-17 13:34 ` [Bug middle-end/20517] " Thomas dot Koenig at online dot de
2005-03-17 17:21 ` [Bug tree-optimization/20517] " pinskia at gcc dot gnu dot org
2005-07-23 21:07 ` phython at gcc dot gnu dot org
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