public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug tree-optimization/19347] New: Invariant load not moved out of loop
@ 2005-01-09 10:51 irar at il dot ibm dot com
2005-01-09 15:55 ` [Bug tree-optimization/19347] " pinskia at gcc dot gnu dot org
2005-04-11 6:10 ` pinskia at gcc dot gnu dot org
0 siblings, 2 replies; 7+ messages in thread
From: irar at il dot ibm dot com @ 2005-01-09 10:51 UTC (permalink / raw)
To: gcc-bugs
In mesa benchmark (osmesa.c:678)
GLuint i, n, *ptr4;
n = osmesa->rowlength * osmesa->height;
ptr4 = (GLuint *) osmesa->buffer;
for (i=0;i<n;i++) {
*ptr4++ = osmesa->clearpixel;
}
The load of osmesa->clearpixel is not taken outside the loop by LIM because of
aliasing limitations. This in turn also prevents vectorization.
In this particular case we can actually get the load moved out of the loop even
without resolving the aliasing issue (which requires whole-program), on
account that even if the store aliases the load, it will not alter the value
loaded (because we store the same value that we loaded).
I'm looking into this in the context of the vectorizer.
--
Summary: Invariant load not moved out of loop
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: tree-optimization
AssignedTo: irar at il dot ibm dot com
ReportedBy: irar at il dot ibm dot com
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: powerpc-apple-darwin7.0.0
GCC host triplet: powerpc-apple-darwin7.0.0
GCC target triplet: powerpc-apple-darwin7.0.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19347
^ permalink raw reply [flat|nested] 7+ messages in thread
[parent not found: <bug-19347-9531@http.gcc.gnu.org/bugzilla/>]
[parent not found: <bug-19347-4@http.gcc.gnu.org/bugzilla/>]
* [Bug tree-optimization/19347] Invariant load not moved out of loop
[not found] <bug-19347-4@http.gcc.gnu.org/bugzilla/>
@ 2024-01-03 19:14 ` phosit at autistici dot org
2024-01-03 19:35 ` phosit at autistici dot org
1 sibling, 0 replies; 7+ messages in thread
From: phosit at autistici dot org @ 2024-01-03 19:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19347
Phosit <phosit at autistici dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |phosit at autistici dot org
--- Comment #9 from Phosit <phosit at autistici dot org> ---
When there are few iterations (likely when it is unroled) there is no
alias-check:
void fill(int* data, int& value)
{
for(unsigned long i{0}; i != 4; ++i)
data[i] = value;
}
--- at -O2 results in:
fill(int*, int&):
movd xmm1, DWORD PTR [rsi]
pshufd xmm0, xmm1, 0xe0
movq QWORD PTR [rdi], xmm0
movd xmm0, DWORD PTR [rsi]
pshufd xmm0, xmm0, 0xe0
movq QWORD PTR [rdi+8], xmm0
ret
---
At -O3 the loop isn't removed and (thus) there is an alias-check.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/19347] Invariant load not moved out of loop
[not found] <bug-19347-4@http.gcc.gnu.org/bugzilla/>
2024-01-03 19:14 ` phosit at autistici dot org
@ 2024-01-03 19:35 ` phosit at autistici dot org
1 sibling, 0 replies; 7+ messages in thread
From: phosit at autistici dot org @ 2024-01-03 19:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19347
--- Comment #10 from Phosit <phosit at autistici dot org> ---
The analysis in my previous comment is wrong.
I don't know why there is no alias-check at -O2.
Also the loop _is_ removed at -O3.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2024-01-03 19:35 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2005-01-09 10:51 [Bug tree-optimization/19347] New: Invariant load not moved out of loop irar at il dot ibm dot com
2005-01-09 15:55 ` [Bug tree-optimization/19347] " pinskia at gcc dot gnu dot org
2005-04-11 6:10 ` pinskia at gcc dot gnu dot org
[not found] <bug-19347-9531@http.gcc.gnu.org/bugzilla/>
2005-10-24 0:20 ` pinskia at gcc dot gnu dot org
2009-04-03 12:06 ` rguenth at gcc dot gnu dot org
[not found] <bug-19347-4@http.gcc.gnu.org/bugzilla/>
2024-01-03 19:14 ` phosit at autistici dot org
2024-01-03 19:35 ` phosit at autistici 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).