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* [Bug tree-optimization/94828] New: Failure to merge merge-able loops
@ 2020-04-28 17:49 gabravier at gmail dot com
2020-04-28 21:52 ` [Bug tree-optimization/94828] Loop fusion is not implemented pinskia at gcc dot gnu.org
2020-04-29 7:02 ` [Bug tree-optimization/94828] Loop fusion is not implemented outside of ISL rguenth at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: gabravier at gmail dot com @ 2020-04-28 17:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94828
Bug ID: 94828
Summary: Failure to merge merge-able loops
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: gabravier at gmail dot com
Target Milestone: ---
void f(int *__restrict a, int *__restrict b, size_t sz)
{
for (int i = 0; i < sz; ++i)
a[i] += b[i];
for (int i = 0; i < sz; ++i)
a[i] += b[i];
}
These two loops could be merged into a single one doing two additions per
iteration. ICC does this transformation, GCC does not.
Also, I'd like to note that from the GCC output, only the first loop is
vectorized, and not the second one.
See https://godbolt.org/z/DfGpSi
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/94828] Loop fusion is not implemented
2020-04-28 17:49 [Bug tree-optimization/94828] New: Failure to merge merge-able loops gabravier at gmail dot com
@ 2020-04-28 21:52 ` pinskia at gcc dot gnu.org
2020-04-29 7:02 ` [Bug tree-optimization/94828] Loop fusion is not implemented outside of ISL rguenth at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu.org @ 2020-04-28 21:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94828
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2020-04-28
Summary|Failure to merge merge-able |Loop fusion is not
|loops |implemented
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Loop fusion is not implemented correct.
See PR 45661 and PR 85531 also.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/94828] Loop fusion is not implemented outside of ISL
2020-04-28 17:49 [Bug tree-optimization/94828] New: Failure to merge merge-able loops gabravier at gmail dot com
2020-04-28 21:52 ` [Bug tree-optimization/94828] Loop fusion is not implemented pinskia at gcc dot gnu.org
@ 2020-04-29 7:02 ` rguenth at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-04-29 7:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94828
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|Loop fusion is not |Loop fusion is not
|implemented |implemented outside of ISL
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Both loops are vectorized:
> ./cc1 -quiet y.c -O3 -fopt-info-vec
y.c:6:11: optimized: loop vectorized using 16 byte vectors
y.c:3:7: optimized: loop vectorized using 16 byte vectors
GCC fuses the loops with -floop-nest-optimize
[scheduler] original ast:
{
for (int c0 = 0; c0 < P_20; c0 += 1)
S_3(c0);
for (int c0 = 0; c0 < P_20; c0 += 1)
S_4(c0);
}
[scheduler] AST generated by isl:
for (int c0 = 0; c0 < P_20; c0 += 1) {
S_3(c0);
S_4(c0);
}
producing
.L4:
movdqu (%rdi,%rax), %xmm0
movdqu (%rsi,%rax), %xmm2
paddd %xmm2, %xmm0
paddd %xmm2, %xmm0
movups %xmm0, (%rdi,%rax)
addq $16, %rax
cmpq %rdx, %rax
jne .L4
but it's true that GCC does not implement classical loop fusion.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-04-29 7:02 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2020-04-28 17:49 [Bug tree-optimization/94828] New: Failure to merge merge-able loops gabravier at gmail dot com
2020-04-28 21:52 ` [Bug tree-optimization/94828] Loop fusion is not implemented pinskia at gcc dot gnu.org
2020-04-29 7:02 ` [Bug tree-optimization/94828] Loop fusion is not implemented outside of ISL rguenth at gcc dot gnu.org
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