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* [Bug middle-end/54571] New: Missed optimization converting between bit sets
@ 2012-09-13 21:25 rth at gcc dot gnu.org
2012-09-13 21:25 ` [Bug middle-end/54571] " rth at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: rth at gcc dot gnu.org @ 2012-09-13 21:25 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54571
Bug #: 54571
Summary: Missed optimization converting between bit sets
Classification: Unclassified
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: rth@gcc.gnu.org
When converting a bit set from one domain to another,code such as
if (old & OLD_X) new |= NEW_X;
if (old & OLD_Y) new |= NEW_Y;
is common. If OLD_X and NEW_X are single bits, then this conversion
need not include any conditional code. One can mask out OLD_X and
shift it left or right to become NEW_X. Or, vice versa, shift left
or right and then mask out NEW_X.
Indeed, it's probably preferable to perform the mask with the smaller
of OLD_X and NEW_X in order to maximize the possibility of having a
valid immediate operand to the logical insn.
A test case that would seem to cover the all the cases, including
converting logical not to bitwise not, would seem to be
int f1(int x, int y) { if (x & 1) y |= 1; return y; }
int f2(int x, int y) { if (x & 1) y |= 2; return y; }
int f3(int x, int y) { if (x & 2) y |= 1; return y; }
int g1(int x, int y) { if (!(x & 1)) y |= 1; return y; }
int g2(int x, int y) { if (!(x & 1)) y |= 2; return y; }
int g3(int x, int y) { if (!(x & 2)) y |= 1; return y; }
I'll also note that on the (presumably) preferred alternatives:
int h1(int x, int y) { return (x & 1) | y; }
int h2(int x, int y) { return ((x & 1) << 1) | y; }
int h3(int x, int y) { return ((x & 2) >> 1) | y; }
int k1(int x, int y) { return (~x & 1) | y; }
int k2(int x, int y) { return ((~x & 1) << 1) | y; }
int k3(int x, int y) { return ((~x >> 1) & 1) | y; }
there's some less-than-optimial code generated for k1 and k2.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/54571] Missed optimization converting between bit sets
2012-09-13 21:25 [Bug middle-end/54571] New: Missed optimization converting between bit sets rth at gcc dot gnu.org
@ 2012-09-13 21:25 ` rth at gcc dot gnu.org
2012-09-14 8:40 ` rguenth at gcc dot gnu.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: rth at gcc dot gnu.org @ 2012-09-13 21:25 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54571
Richard Henderson <rth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Severity|normal |enhancement
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/54571] Missed optimization converting between bit sets
2012-09-13 21:25 [Bug middle-end/54571] New: Missed optimization converting between bit sets rth at gcc dot gnu.org
2012-09-13 21:25 ` [Bug middle-end/54571] " rth at gcc dot gnu.org
@ 2012-09-14 8:40 ` rguenth at gcc dot gnu.org
2021-07-06 8:39 ` pinskia at gcc dot gnu.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu.org @ 2012-09-14 8:40 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54571
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2012-09-14
Version|unknown |4.8.0
Ever Confirmed|0 |1
--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-09-14 08:39:42 UTC ---
Confirmed. The natural place to optimize this is the tree level phiopt pass.
<bb 2>:
_3 = x_2(D) & 2;
if (_3 != 0)
goto <bb 3>;
else
goto <bb 4>;
<bb 3>:
y_5 = y_4(D) | 1;
<bb 4>:
# y_1 = PHI <y_4(D)(2), y_5(3)>
where we should handle
int f1(int x, int y, int d) { int tem; if ((tem = x & d)) y |= tem; return y; }
as well. Yes, that's just y |= x & d, but it falls out naturally if the
transform is implemented in a generic enough way.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/54571] Missed optimization converting between bit sets
2012-09-13 21:25 [Bug middle-end/54571] New: Missed optimization converting between bit sets rth at gcc dot gnu.org
2012-09-13 21:25 ` [Bug middle-end/54571] " rth at gcc dot gnu.org
2012-09-14 8:40 ` rguenth at gcc dot gnu.org
@ 2021-07-06 8:39 ` pinskia at gcc dot gnu.org
2021-07-20 3:16 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-07-06 8:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54571
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #1)
> Confirmed. The natural place to optimize this is the tree level phiopt pass.
>
> <bb 2>:
> _3 = x_2(D) & 2;
> if (_3 != 0)
> goto <bb 3>;
> else
> goto <bb 4>;
>
> <bb 3>:
> y_5 = y_4(D) | 1;
>
> <bb 4>:
> # y_1 = PHI <y_4(D)(2), y_5(3)>
>
> where we should handle
>
> int f1(int x, int y, int d) { int tem; if ((tem = x & d)) y |= tem; return
> y; }
>
> as well. Yes, that's just y |= x & d, but it falls out naturally if the
> transform is implemented in a generic enough way.
This one should be easy to add to match.pd:
(simplify
(cond @1 (ior @2 INTEGER_CST@3) @2)
(ior @2 (bit_and (negate (convert @1)) @3)))
(bit_and (negate (convert thurth_value@1)) integer_onep)
should be just converted to:
@1
Which is not done right now, I fill that as a bug.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/54571] Missed optimization converting between bit sets
2012-09-13 21:25 [Bug middle-end/54571] New: Missed optimization converting between bit sets rth at gcc dot gnu.org
` (2 preceding siblings ...)
2021-07-06 8:39 ` pinskia at gcc dot gnu.org
@ 2021-07-20 3:16 ` pinskia at gcc dot gnu.org
2021-11-15 0:52 ` pinskia at gcc dot gnu.org
2023-06-07 15:20 ` pinskia at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-07-20 3:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54571
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |dhowells at redhat dot com
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 78317 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/54571] Missed optimization converting between bit sets
2012-09-13 21:25 [Bug middle-end/54571] New: Missed optimization converting between bit sets rth at gcc dot gnu.org
` (3 preceding siblings ...)
2021-07-20 3:16 ` pinskia at gcc dot gnu.org
@ 2021-11-15 0:52 ` pinskia at gcc dot gnu.org
2023-06-07 15:20 ` pinskia at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-11-15 0:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54571
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |pinskia at gcc dot gnu.org
Status|NEW |ASSIGNED
Depends on| |103216
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is fixed mostly by the patch which fixes PR 103216.
We still have stuff like:
_1 = x_3(D) & 1;
_7 = _1 != 0;
_8 = (int) _7;
_9 = y_4(D) | _8;
and:
_1 = x_3(D) & 2;
_7 = _1 != 0;
_8 = (int) _7;
_9 = y_4(D) | _8;
and
_1 = x_3(D) & 2;
_7 = _1 != 0;
_8 = (int) _7;
_9 = _8 << 1;
_10 = y_4(D) | _9;
Which we produce things like:
xorl %eax, %eax
andl $2, %edi
sete %al
orl %esi, %eax
Where the sete/xor could be reproduced with shift for an example.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103216
[Bug 103216] missed optimization, phiopt/vrp?
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/54571] Missed optimization converting between bit sets
2012-09-13 21:25 [Bug middle-end/54571] New: Missed optimization converting between bit sets rth at gcc dot gnu.org
` (4 preceding siblings ...)
2021-11-15 0:52 ` pinskia at gcc dot gnu.org
@ 2023-06-07 15:20 ` pinskia at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-06-07 15:20 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54571
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The `popcount(nz) == 1` comment part of PR 103216 will fix this issue.
^ permalink raw reply [flat|nested] 7+ messages in thread
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2012-09-13 21:25 [Bug middle-end/54571] New: Missed optimization converting between bit sets rth at gcc dot gnu.org
2012-09-13 21:25 ` [Bug middle-end/54571] " rth at gcc dot gnu.org
2012-09-14 8:40 ` rguenth at gcc dot gnu.org
2021-07-06 8:39 ` pinskia at gcc dot gnu.org
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