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* [Bug tree-optimization/32806] New: Missing optimization to remove backword dependencies
@ 2007-07-18 9:58 irar at il dot ibm dot com
2007-07-19 18:07 ` [Bug tree-optimization/32806] " rguenth at gcc dot gnu dot org
0 siblings, 1 reply; 2+ messages in thread
From: irar at il dot ibm dot com @ 2007-07-18 9:58 UTC (permalink / raw)
To: gcc-bugs
for (i=0; i<N; i++)
{
D[i] = A[i] + Y;
A[i+1] = B[i] + X;
}
Even though, this loop contains a backward-carried dependence between A[i+1]
and A[i], it is vectorizable - the stmts of the loop should be interchanged to
get:
for (i=0; i<N; i++)
{
A[i+1] = B[i] + X;
D[i] = A[i] + Y;
}
which will be vectorizable once the pacth in PR 32377 (comment #14) is
committed.
The interchange is possible since there is no loop-independent dependence
between the stmts. This requires working with a dependence graph when
vectorizing, or have a separate optimization before the vectorizer to take care
of this.
Ira
--
Summary: Missing optimization to remove backword dependencies
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: irar at il dot ibm dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32806
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug tree-optimization/32806] Missing optimization to remove backword dependencies
2007-07-18 9:58 [Bug tree-optimization/32806] New: Missing optimization to remove backword dependencies irar at il dot ibm dot com
@ 2007-07-19 18:07 ` rguenth at gcc dot gnu dot org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2007-07-19 18:07 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from rguenth at gcc dot gnu dot org 2007-07-19 18:07 -------
Confirmed.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu dot
| |org
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2007-07-19 18:07:11
date| |
Summary|Missing optimization to |Missing optimization to
|remove backword dependencies|remove backword dependencies
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32806
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2007-07-18 9:58 [Bug tree-optimization/32806] New: Missing optimization to remove backword dependencies irar at il dot ibm dot com
2007-07-19 18:07 ` [Bug tree-optimization/32806] " rguenth at gcc dot gnu dot org
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