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* [Bug tree-optimization/45215] New: Tree-optimization misses a trick with bit tests
@ 2010-08-06 21:29 bernds at gcc dot gnu dot org
2010-08-06 21:49 ` [Bug tree-optimization/45215] " rguenth at gcc dot gnu dot org
0 siblings, 1 reply; 2+ messages in thread
From: bernds at gcc dot gnu dot org @ 2010-08-06 21:29 UTC (permalink / raw)
To: gcc-bugs
The following testcase
int x (int t)
{
if (t & 256)
return -26;
return 0;
}
can be implemented as a sequence of two shifts and one and operation:
movl 4(%esp), %eax
sall $23, %eax
sarl $31, %eax
andl $-26, %eax
ret
Initial RTL generation produces a more complicated sequence which is not
optimized unless the combiner is extended to handle four insns. The tree
optimizers could be enhanced to handle this pattern and related ones, although
it would have to take costs into account, as on some targets other sequences
may be better.
--
Summary: Tree-optimization misses a trick with bit tests
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: bernds at gcc dot gnu dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45215
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug tree-optimization/45215] Tree-optimization misses a trick with bit tests
2010-08-06 21:29 [Bug tree-optimization/45215] New: Tree-optimization misses a trick with bit tests bernds at gcc dot gnu dot org
@ 2010-08-06 21:49 ` rguenth at gcc dot gnu dot org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2010-08-06 21:49 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from rguenth at gcc dot gnu dot org 2010-08-06 21:49 -------
Confirmed.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC|richard dot guenther at |rguenth at gcc dot gnu dot
|gmail dot com |org
Severity|normal |enhancement
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Keywords| |missed-optimization
Last reconfirmed|0000-00-00 00:00:00 |2010-08-06 21:49:25
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45215
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2010-08-06 21:29 [Bug tree-optimization/45215] New: Tree-optimization misses a trick with bit tests bernds at gcc dot gnu dot org
2010-08-06 21:49 ` [Bug tree-optimization/45215] " rguenth at gcc dot gnu dot org
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