public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug middle-end/35344] New: Loop unswitching to produce perfect loop nest
@ 2008-02-24 4:33 xinliangli at gmail dot com
2008-02-24 21:55 ` [Bug tree-optimization/35344] " rguenth at gcc dot gnu dot org
0 siblings, 1 reply; 2+ messages in thread
From: xinliangli at gmail dot com @ 2008-02-24 4:33 UTC (permalink / raw)
To: gcc-bugs
GCC loop unswitching is very good -- handles most of the cases I tried. The
only only thing I notice is that the nested for loops in C in the example below
is not converted into a perfect loop nest:
int** p;
int** q;
void foo(int m, int n)
{
int i, j;
for (i = 0; i < m; i++)
{
for (j = 0; j < n ; j++)
{
p[i][j] += q[i][j];
q[i][j] ++;
}
}
}
It is generated into (roughly) the following code by gcc (-O3
-fno-tree-vectorize)
if (m > 0)
{
do
{
if (n > 0 )
{
do
{
p[i][j] += q[i][j];
q[i][j] += 1;
j += 1;
} while ( j < n);
}
i+=1;
} while (i < m);
}
Ideally-- it should be:
if (m > 0)
{
if (n >0)
{
do
{
do
{
....
j++;
} while(...);
i++;
}while (...);
}
// empty loop deleted
}
--
Summary: Loop unswitching to produce perfect loop nest
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: xinliangli at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35344
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug tree-optimization/35344] Loop unswitching to produce perfect loop nest
2008-02-24 4:33 [Bug middle-end/35344] New: Loop unswitching to produce perfect loop nest xinliangli at gmail dot com
@ 2008-02-24 21:55 ` rguenth at gcc dot gnu dot org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2008-02-24 21:55 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from rguenth at gcc dot gnu dot org 2008-02-24 21:54 -------
I think this is a dup of PR23855.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rakdver at gcc dot gnu dot
| |org
Severity|normal |enhancement
Component|middle-end |tree-optimization
Keywords| |missed-optimization
Version|unknown |4.3.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35344
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2008-02-24 21:55 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-02-24 4:33 [Bug middle-end/35344] New: Loop unswitching to produce perfect loop nest xinliangli at gmail dot com
2008-02-24 21:55 ` [Bug tree-optimization/35344] " rguenth at gcc dot gnu dot org
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).