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* [Bug rtl-optimization/101806] New: Extra zero extends for some arguments in some cases
@ 2021-08-06 21:10 pinskia at gcc dot gnu.org
2021-08-06 21:13 ` [Bug rtl-optimization/101806] " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-08-06 21:10 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101806
Bug ID: 101806
Summary: Extra zero extends for some arguments in some cases
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Target: aarch64-*-*
Take:
bool g(bool a, bool b)
{
return ~a & b;
}
---- CUT ---
Currently we produce:
and w1, w1, 255
and w0, w0, 255
bic w0, w1, w0
and w0, w0, 1
---- CUT ---
But we should produce:
bic w0, w1, w0
and w0, w0, 1
The zero extends are not needed.
This happens because combine does the correct thing until it tries to figure
out the cutting point:Trying 2, 8 -> 16:
2: r98:SI=zero_extend(x0:QI)
REG_DEAD x0:QI
8: r102:SI=~r98:SI&r99:SI
REG_DEAD r98:SI
REG_DEAD r99:SI
16: x0:SI=r102:SI&0x1
REG_DEAD r102:SI
Failed to match this instruction:
(set (reg:SI 0 x0)
(and:SI (and:SI (not:SI (reg:SI 0 x0 [ a ]))
(reg/v:SI 99 [ b ]))
(const_int 1 [0x1])))
Successfully matched this instruction:
(set (reg:SI 102)
(not:SI (reg:SI 0 x0 [ a ])))
Failed to match this instruction:
(set (reg:SI 0 x0)
(and:SI (and:SI (reg:SI 102)
(reg/v:SI 99 [ b ]))
(const_int 1 [0x1])))
If we had chose (and:SI (not:SI (reg:SI 0 x0 [ a ])) (reg/v:SI 99 [ b ]))
instead, we would have gotten the correct thing.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug rtl-optimization/101806] Extra zero extends for some arguments in some cases
2021-08-06 21:10 [Bug rtl-optimization/101806] New: Extra zero extends for some arguments in some cases pinskia at gcc dot gnu.org
@ 2021-08-06 21:13 ` pinskia at gcc dot gnu.org
2022-10-27 3:21 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-08-06 21:13 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101806
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It happens to work on x86-64(with -march=skylake-avx512) becausewe get a
zero_extend instead of an and there. I still don't understand how x86 is able
to figure out the &1 part.
Trying 11, 9 -> 12:
11: r94:SI=zero_extend(r97:SI#0)
REG_DEAD r97:SI
9: r92:SI=zero_extend(r96:SI#0)
REG_DEAD r96:SI
12: {r95:SI=~r92:SI&r94:SI;clobber flags:CC;}
REG_DEAD r92:SI
REG_UNUSED flags:CC
REG_DEAD r94:SI
Failed to match this instruction:
(parallel [
(set (reg:SI 95)
(zero_extend:SI (and:QI (not:QI (subreg:QI (reg:SI 96) 0))
(subreg:QI (reg:SI 97) 0))))
(clobber (reg:CC 17 flags))
])
Failed to match this instruction:
(set (reg:SI 95)
(zero_extend:SI (and:QI (not:QI (subreg:QI (reg:SI 96) 0))
(subreg:QI (reg:SI 97) 0))))
Successfully matched this instruction:
(set (reg:QI 94 [ b ])
(and:QI (not:QI (subreg:QI (reg:SI 96) 0))
(subreg:QI (reg:SI 97) 0)))
Successfully matched this instruction:
(set (reg:SI 95)
(zero_extend:SI (reg:QI 94 [ b ])))
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug rtl-optimization/101806] Extra zero extends for some arguments in some cases
2021-08-06 21:10 [Bug rtl-optimization/101806] New: Extra zero extends for some arguments in some cases pinskia at gcc dot gnu.org
2021-08-06 21:13 ` [Bug rtl-optimization/101806] " pinskia at gcc dot gnu.org
@ 2022-10-27 3:21 ` pinskia at gcc dot gnu.org
2022-12-25 5:30 ` pinskia at gcc dot gnu.org
2023-05-12 17:48 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-10-27 3:21 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101806
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this will be fixed/improved by
https://gcc.gnu.org/pipermail/gcc-patches/2022-September/602089.html .
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug rtl-optimization/101806] Extra zero extends for some arguments in some cases
2021-08-06 21:10 [Bug rtl-optimization/101806] New: Extra zero extends for some arguments in some cases pinskia at gcc dot gnu.org
2021-08-06 21:13 ` [Bug rtl-optimization/101806] " pinskia at gcc dot gnu.org
2022-10-27 3:21 ` pinskia at gcc dot gnu.org
@ 2022-12-25 5:30 ` pinskia at gcc dot gnu.org
2023-05-12 17:48 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-12-25 5:30 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101806
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Even a simple:
unsigned char g(unsigned char a, unsigned char b)
{
return ((~a) & b)&1;
}
Produces the extra zero extend.
But it is ok with:
unsigned char g(unsigned char *a, unsigned char *b)
{
return ((~*a) & *b)&1;
}
It looks like it is hard register related too ...
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug rtl-optimization/101806] Extra zero extends for some arguments in some cases
2021-08-06 21:10 [Bug rtl-optimization/101806] New: Extra zero extends for some arguments in some cases pinskia at gcc dot gnu.org
` (2 preceding siblings ...)
2022-12-25 5:30 ` pinskia at gcc dot gnu.org
@ 2023-05-12 17:48 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-05-12 17:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101806
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |acoplan at gcc dot gnu.org
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 109832 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2023-05-12 17:48 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2021-08-06 21:10 [Bug rtl-optimization/101806] New: Extra zero extends for some arguments in some cases pinskia at gcc dot gnu.org
2021-08-06 21:13 ` [Bug rtl-optimization/101806] " pinskia at gcc dot gnu.org
2022-10-27 3:21 ` pinskia at gcc dot gnu.org
2022-12-25 5:30 ` pinskia at gcc dot gnu.org
2023-05-12 17:48 ` pinskia at gcc dot gnu.org
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