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* [Bug tree-optimization/45671] New: Reassociate expressions for greater parallelism
@ 2010-09-14 20:14 pthaugen at gcc dot gnu dot org
2010-09-15 4:29 ` [Bug tree-optimization/45671] " hjl dot tools at gmail dot com
0 siblings, 1 reply; 2+ messages in thread
From: pthaugen at gcc dot gnu dot org @ 2010-09-14 20:14 UTC (permalink / raw)
To: gcc-bugs
The following testcase demonstrates where reassociation/regrouping of
expressions could result in greater parallelism for processors that have
multiple arithmetic execution units.
int myfunction (int a, int b, int c, int d, int e, int f, int g, int h) {
int ret;
ret = a + b + c + d + e + f + g + h;
return ret;
}
Compiling with -O3 results in a series of dependent add instructions to
accumulate the sum.
add 4,3,4
add 4,4,5
add 4,4,6
add 4,4,7
add 4,4,8
add 4,4,9
add 4,4,10
If we regrouped to (a+b)+(c+d)+... we can do multiple adds in parallel on
different execution units.
--
Summary: Reassociate expressions for greater parallelism
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: pthaugen at gcc dot gnu dot org
GCC build triplet: powerpc64-unknown-linux-gnu
GCC host triplet: powerpc64-unknown-linux-gnu
GCC target triplet: powerpc64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45671
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug tree-optimization/45671] Reassociate expressions for greater parallelism
2010-09-14 20:14 [Bug tree-optimization/45671] New: Reassociate expressions for greater parallelism pthaugen at gcc dot gnu dot org
@ 2010-09-15 4:29 ` hjl dot tools at gmail dot com
0 siblings, 0 replies; 2+ messages in thread
From: hjl dot tools at gmail dot com @ 2010-09-15 4:29 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from hjl dot tools at gmail dot com 2010-09-15 04:29 -------
*** This bug has been marked as a duplicate of 44382 ***
--
hjl dot tools at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
GCC build triplet|powerpc64-unknown-linux-gnu |
GCC host triplet|powerpc64-unknown-linux-gnu |
GCC target triplet|powerpc64-unknown-linux-gnu |
Resolution| |DUPLICATE
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45671
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2010-09-14 20:14 [Bug tree-optimization/45671] New: Reassociate expressions for greater parallelism pthaugen at gcc dot gnu dot org
2010-09-15 4:29 ` [Bug tree-optimization/45671] " hjl dot tools at gmail dot com
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