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* [Bug tree-optimization/31261] New: Missed tree optimizations: (8 - (x & 7)) & 7
@ 2007-03-19 11:05 jakub at gcc dot gnu dot org
2007-03-19 11:17 ` [Bug tree-optimization/31261] " rguenth at gcc dot gnu dot org
` (3 more replies)
0 siblings, 4 replies; 6+ messages in thread
From: jakub at gcc dot gnu dot org @ 2007-03-19 11:05 UTC (permalink / raw)
To: gcc-bugs
In 4.2 with -O2 -m32 -fomit-frame-pointer on x86_64:
unsigned int foo (unsigned int x)
{
return (8 - (x & 7)) & 7;
}
results in andl $7, reg; negl reg; andl $7, reg.
On 4.3 apparently some RTL optimization catches this, but it is still a missed
tree optimization, fold should be able to fold:
(cst - (x & cstmask)) & cstmask2 as
(cst & cstmask2) + (-x & cstmask2) if x is unsigned or if -INT_MIN wraps to
INT_MIN, both cstmask and cstmask2 are constants z^2-1 for some z and
(cstmask & cstmask2) == cstmask2.
BTW, even for
(8 + (x & 7)) & 7
the optimized dump contains:
(x & 7) + 8 & 7
for both 4.2/4.3 (no idea why 8 & 7 hasn't been simplified as 0).
--
Summary: Missed tree optimizations: (8 - (x & 7)) & 7
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jakub at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31261
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug tree-optimization/31261] Missed tree optimizations: (8 - (x & 7)) & 7 2007-03-19 11:05 [Bug tree-optimization/31261] New: Missed tree optimizations: (8 - (x & 7)) & 7 jakub at gcc dot gnu dot org @ 2007-03-19 11:17 ` rguenth at gcc dot gnu dot org 2007-03-19 11:19 ` rguenth at gcc dot gnu dot org ` (2 subsequent siblings) 3 siblings, 0 replies; 6+ messages in thread From: rguenth at gcc dot gnu dot org @ 2007-03-19 11:17 UTC (permalink / raw) To: gcc-bugs ------- Comment #1 from rguenth at gcc dot gnu dot org 2007-03-19 11:17 ------- (x & 7) + 8 & 7 is actually ((x & 7) + 8) & 7 -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31261 ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/31261] Missed tree optimizations: (8 - (x & 7)) & 7 2007-03-19 11:05 [Bug tree-optimization/31261] New: Missed tree optimizations: (8 - (x & 7)) & 7 jakub at gcc dot gnu dot org 2007-03-19 11:17 ` [Bug tree-optimization/31261] " rguenth at gcc dot gnu dot org @ 2007-03-19 11:19 ` rguenth at gcc dot gnu dot org 2007-03-21 15:06 ` jakub at gcc dot gnu dot org 2007-03-21 18:28 ` trt at acm dot org 3 siblings, 0 replies; 6+ messages in thread From: rguenth at gcc dot gnu dot org @ 2007-03-19 11:19 UTC (permalink / raw) To: gcc-bugs ------- Comment #2 from rguenth at gcc dot gnu dot org 2007-03-19 11:19 ------- You would need to enhance associate_trees () or the reassoc pass to fix this. -- rguenth at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- Severity|normal |enhancement Status|UNCONFIRMED |NEW Ever Confirmed|0 |1 Keywords| |missed-optimization, TREE Last reconfirmed|0000-00-00 00:00:00 |2007-03-19 11:19:48 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31261 ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/31261] Missed tree optimizations: (8 - (x & 7)) & 7 2007-03-19 11:05 [Bug tree-optimization/31261] New: Missed tree optimizations: (8 - (x & 7)) & 7 jakub at gcc dot gnu dot org 2007-03-19 11:17 ` [Bug tree-optimization/31261] " rguenth at gcc dot gnu dot org 2007-03-19 11:19 ` rguenth at gcc dot gnu dot org @ 2007-03-21 15:06 ` jakub at gcc dot gnu dot org 2007-03-21 18:28 ` trt at acm dot org 3 siblings, 0 replies; 6+ messages in thread From: jakub at gcc dot gnu dot org @ 2007-03-21 15:06 UTC (permalink / raw) To: gcc-bugs ------- Comment #3 from jakub at gcc dot gnu dot org 2007-03-21 15:05 ------- Created an attachment (id=13244) --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=13244&action=view) gcc43-pr31261.patch Patch I'm testing ATM. -- jakub at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- AssignedTo|unassigned at gcc dot gnu |jakub at gcc dot gnu dot org |dot org | Status|NEW |ASSIGNED http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31261 ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/31261] Missed tree optimizations: (8 - (x & 7)) & 7 2007-03-19 11:05 [Bug tree-optimization/31261] New: Missed tree optimizations: (8 - (x & 7)) & 7 jakub at gcc dot gnu dot org ` (2 preceding siblings ...) 2007-03-21 15:06 ` jakub at gcc dot gnu dot org @ 2007-03-21 18:28 ` trt at acm dot org 3 siblings, 0 replies; 6+ messages in thread From: trt at acm dot org @ 2007-03-21 18:28 UTC (permalink / raw) To: gcc-bugs ------- Comment #4 from trt at acm dot org 2007-03-21 18:28 ------- I think this could be generalized to more operators, e.g. (y | (x & 7)) & 7 ^ (bitwise or, xor, multiply, ...) This optimization could be for "e & M" where e contains a subexpression of the form "t & N" which can (sometimes) be simplified to "t". I suppose that would require walking the tree. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31261 ^ permalink raw reply [flat|nested] 6+ messages in thread
[parent not found: <bug-31261-4@http.gcc.gnu.org/bugzilla/>]
* [Bug tree-optimization/31261] Missed tree optimizations: (8 - (x & 7)) & 7 [not found] <bug-31261-4@http.gcc.gnu.org/bugzilla/> @ 2010-09-30 21:23 ` jakub at gcc dot gnu.org 0 siblings, 0 replies; 6+ messages in thread From: jakub at gcc dot gnu.org @ 2010-09-30 21:23 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31261 --- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2010-09-30 19:21:44 UTC --- Author: jakub Date: Thu Sep 30 19:21:34 2010 New Revision: 164761 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=164761 Log: PR tree-optimization/31261 * fold-const.c (fold_binary): Optimize ((A & N) + B) & M for constants M and N, M == (1LL << cst) - 1 && (N & M) == M. * gcc.dg/tree-ssa/pr31261.c: New test. Added: trunk/gcc/testsuite/gcc.dg/tree-ssa/pr31261.c Modified: trunk/gcc/ChangeLog trunk/gcc/fold-const.c trunk/gcc/testsuite/ChangeLog ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2010-09-30 19:21 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2007-03-19 11:05 [Bug tree-optimization/31261] New: Missed tree optimizations: (8 - (x & 7)) & 7 jakub at gcc dot gnu dot org
2007-03-19 11:17 ` [Bug tree-optimization/31261] " rguenth at gcc dot gnu dot org
2007-03-19 11:19 ` rguenth at gcc dot gnu dot org
2007-03-21 15:06 ` jakub at gcc dot gnu dot org
2007-03-21 18:28 ` trt at acm dot org
[not found] <bug-31261-4@http.gcc.gnu.org/bugzilla/>
2010-09-30 21:23 ` jakub at gcc dot gnu.org
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