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* [Bug middle-end/114647] New: missing DCE when looping over a VLA
@ 2024-04-08 21:37 franckbehaghel_gcc at protonmail dot com
2024-04-08 21:40 ` [Bug tree-optimization/114647] missing DSE " pinskia at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: franckbehaghel_gcc at protonmail dot com @ 2024-04-08 21:37 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114647
Bug ID: 114647
Summary: missing DCE when looping over a VLA
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: franckbehaghel_gcc at protonmail dot com
Target Milestone: ---
$cat foo.cpp
#include "stdint.h"
#include "stdio.h"
void foo(int n)
{
uint64_t a[n];
for (uint32_t i=0;i<n;i++) a[i] = i;
printf(" ");
}
At O3, gcc vectorize the loop but do not remove it:
foo(int):
push rbp
movsx rax, edi
lea rax, [15+rax*8]
and rax, -16
mov rbp, rsp
sub rsp, rax
test edi, edi
je .L2
lea edx, [rdi-1]
cmp edx, 2
jbe .L2
shr edi, 2
mov ecx, 4
pxor xmm2, xmm2
mov rax, rsp
mov edx, edi
movdqa xmm1, XMMWORD PTR .LC0[rip]
movd xmm4, ecx
sal rdx, 5
pshufd xmm4, xmm4, 0
add rdx, rsp
.L4:
movdqa xmm0, xmm1
add rax, 32
paddd xmm1, xmm4
movdqa xmm3, xmm0
punpckhdq xmm0, xmm2
punpckldq xmm3, xmm2
movups XMMWORD PTR [rax-16], xmm0
movups XMMWORD PTR [rax-32], xmm3
cmp rdx, rax
jne .L4
.L2:
mov edi, 32
call putchar
leave
ret
clang ( c or c++ ) does remove the loop :
foo: # @foo
mov edi, 32
jmp putchar@PLT # TAILCALL
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/114647] missing DSE when looping over a VLA
2024-04-08 21:37 [Bug middle-end/114647] New: missing DCE when looping over a VLA franckbehaghel_gcc at protonmail dot com
@ 2024-04-08 21:40 ` pinskia at gcc dot gnu.org
2024-04-08 21:46 ` pinskia at gcc dot gnu.org
2024-04-09 7:12 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-08 21:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114647
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Severity|normal |enhancement
Component|middle-end |tree-optimization
Summary|missing DCE when looping |missing DSE when looping
|over a VLA |over a VLA
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/114647] missing DSE when looping over a VLA
2024-04-08 21:37 [Bug middle-end/114647] New: missing DCE when looping over a VLA franckbehaghel_gcc at protonmail dot com
2024-04-08 21:40 ` [Bug tree-optimization/114647] missing DSE " pinskia at gcc dot gnu.org
@ 2024-04-08 21:46 ` pinskia at gcc dot gnu.org
2024-04-09 7:12 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-08 21:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114647
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2024-04-08
Ever confirmed|0 |1
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC also does not delete allocated memory when used in loop:
```
void foo(int n)
{
{
int *a = __builtin_malloc(n*sizeof(int));
for (int i=0;i<n;i++) a[i] = i;
__builtin_free(a);
}
printf(" ");
}
```
Let me find the dup.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/114647] missing DSE when looping over a VLA
2024-04-08 21:37 [Bug middle-end/114647] New: missing DCE when looping over a VLA franckbehaghel_gcc at protonmail dot com
2024-04-08 21:40 ` [Bug tree-optimization/114647] missing DSE " pinskia at gcc dot gnu.org
2024-04-08 21:46 ` pinskia at gcc dot gnu.org
@ 2024-04-09 7:12 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-04-09 7:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114647
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org
Status|NEW |ASSIGNED
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
/* If we visit this PHI by following a backedge then we
have to make sure ref->ref only refers to SSA names
that are invariant with respect to the loop
represented by this PHI node. */
if (dominated_by_p (CDI_DOMINATORS, gimple_bb (stmt),
gimple_bb (use_stmt))
&& !for_each_index (ref->ref ? &ref->ref :
&ref->base,
check_name, gimple_bb
(use_stmt)))
return DSE_STORE_LIVE;
we could make this bail-out "delayed" until we hit the next possible use in
the loop (of which there is none).
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2024-04-09 7:12 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2024-04-08 21:37 [Bug middle-end/114647] New: missing DCE when looping over a VLA franckbehaghel_gcc at protonmail dot com
2024-04-08 21:40 ` [Bug tree-optimization/114647] missing DSE " pinskia at gcc dot gnu.org
2024-04-08 21:46 ` pinskia at gcc dot gnu.org
2024-04-09 7:12 ` rguenth at gcc dot gnu.org
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