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* [Bug tree-optimization/37700] New: [alias-improvements-branch] redundant load doesn't get eliminated
@ 2008-10-01 14:35 dorit at gcc dot gnu dot org
2008-10-01 15:34 ` [Bug tree-optimization/37700] " rguenth at gcc dot gnu dot org
2009-01-03 0:36 ` rguenth at gcc dot gnu dot org
0 siblings, 2 replies; 3+ messages in thread
From: dorit at gcc dot gnu dot org @ 2008-10-01 14:35 UTC (permalink / raw)
To: gcc-bugs
This happens in testcase gcc.dg/vect/slp-19.c:
The problem is with the loop at line 17: with trunk we detect that one of
the elements of array 'in' is read twice, so we generate overall 8 loads
(reusing one of them). On the alias branch we do not eliminate the extra
load. All the reads and write are from/to local arrays, by the way. This
results in 9 loads, which the vectorizer interperts as a complicated SLP
permutation, so instead it is vectorized across iterations rather than
using SLP:
> "
> slp-19.c:17: note: Load permutation 0 1 2 4 5 6 7 8
> slp-19.c:17: note: Build SLP failed: unsupported load permutation out
> [D.2646_11] = D.2647_12;
> "
--
Summary: [alias-improvements-branch] redundant load doesn't get
eliminated
Product: gcc
Version: unknown
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: dorit at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37700
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/37700] [alias-improvements-branch] redundant load doesn't get eliminated 2008-10-01 14:35 [Bug tree-optimization/37700] New: [alias-improvements-branch] redundant load doesn't get eliminated dorit at gcc dot gnu dot org @ 2008-10-01 15:34 ` rguenth at gcc dot gnu dot org 2009-01-03 0:36 ` rguenth at gcc dot gnu dot org 1 sibling, 0 replies; 3+ messages in thread From: rguenth at gcc dot gnu dot org @ 2008-10-01 15:34 UTC (permalink / raw) To: gcc-bugs ------- Comment #1 from rguenth at gcc dot gnu dot org 2008-10-01 15:33 ------- Smaller testcase, FRE should remove the redundancy but doesn't. unsigned int out[16]; unsigned int in[16]; unsigned int ia[16]; int foo (void) { unsigned int i; for (i = 0; i < 16; ++i) { out[i] = in[i]; ia[i] = in[i]; } } this is because we include VOPs in the value-numbering but fail to value-number them properly to account for non-aliased stores. -- rguenth 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 |2008-10-01 15:33:28 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37700 ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/37700] [alias-improvements-branch] redundant load doesn't get eliminated 2008-10-01 14:35 [Bug tree-optimization/37700] New: [alias-improvements-branch] redundant load doesn't get eliminated dorit at gcc dot gnu dot org 2008-10-01 15:34 ` [Bug tree-optimization/37700] " rguenth at gcc dot gnu dot org @ 2009-01-03 0:36 ` rguenth at gcc dot gnu dot org 1 sibling, 0 replies; 3+ messages in thread From: rguenth at gcc dot gnu dot org @ 2009-01-03 0:36 UTC (permalink / raw) To: gcc-bugs ------- Comment #2 from rguenth at gcc dot gnu dot org 2009-01-03 00:33 ------- This is fixed on the branch. -- rguenth at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution| |FIXED http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37700 ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2009-01-03 0:36 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2008-10-01 14:35 [Bug tree-optimization/37700] New: [alias-improvements-branch] redundant load doesn't get eliminated dorit at gcc dot gnu dot org 2008-10-01 15:34 ` [Bug tree-optimization/37700] " rguenth at gcc dot gnu dot org 2009-01-03 0:36 ` rguenth at gcc dot gnu dot org
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