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* [Bug middle-end/114661] New: Bit operations not optimized to multiplication
@ 2024-04-09 16:11 antoshkka at gmail dot com
2024-04-09 19:55 ` [Bug middle-end/114661] " pinskia at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: antoshkka at gmail dot com @ 2024-04-09 16:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114661
Bug ID: 114661
Summary: Bit operations not optimized to multiplication
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: antoshkka at gmail dot com
Target Milestone: ---
Consider the example:
unsigned mul(unsigned char c) {
if (c > 3) __builtin_unreachable();
return c << 18 | c << 15 |
c << 12 | c << 9 |
c << 6 | c << 3 | c;
}
GCC with -O2 generates the following assembly:
mul(unsigned char):
movzx edi, dil
lea edx, [rdi+rdi*8]
lea eax, [0+rdx*8]
mov ecx, edx
sal edx, 15
or eax, edi
sal ecx, 9
or eax, ecx
or eax, edx
ret
However it could be optimized to just:
mul(unsigned char):
imul eax, edi, 299593
ret
Compiling with -Os does not help.
Godbolt playground: https://godbolt.org/z/YszzMbovK
P.S.: without `c << 18 | c << 15 |` the bit operations are transformed to
multiplication.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/114661] Bit operations not optimized to multiplication
2024-04-09 16:11 [Bug middle-end/114661] New: Bit operations not optimized to multiplication antoshkka at gmail dot com
@ 2024-04-09 19:55 ` pinskia at gcc dot gnu.org
2024-04-09 19:57 ` pinskia at gcc dot gnu.org
2024-04-09 22:04 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-09 19:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114661
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/114661] Bit operations not optimized to multiplication
2024-04-09 16:11 [Bug middle-end/114661] New: Bit operations not optimized to multiplication antoshkka at gmail dot com
2024-04-09 19:55 ` [Bug middle-end/114661] " pinskia at gcc dot gnu.org
@ 2024-04-09 19:57 ` pinskia at gcc dot gnu.org
2024-04-09 22:04 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-09 19:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114661
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |pinskia at gcc dot gnu.org
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Seems like another example where -fwrapv improves code ...
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/114661] Bit operations not optimized to multiplication
2024-04-09 16:11 [Bug middle-end/114661] New: Bit operations not optimized to multiplication antoshkka at gmail dot com
2024-04-09 19:55 ` [Bug middle-end/114661] " pinskia at gcc dot gnu.org
2024-04-09 19:57 ` pinskia at gcc dot gnu.org
@ 2024-04-09 22:04 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-09 22:04 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114661
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2024-04-09
Ever confirmed|0 |1
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2024-04-09 22:04 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2024-04-09 16:11 [Bug middle-end/114661] New: Bit operations not optimized to multiplication antoshkka at gmail dot com
2024-04-09 19:55 ` [Bug middle-end/114661] " pinskia at gcc dot gnu.org
2024-04-09 19:57 ` pinskia at gcc dot gnu.org
2024-04-09 22:04 ` pinskia at gcc dot gnu.org
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