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* [Bug tree-optimization/106727] New: Missed fold / canonicalization for checking if a number is a power of 2
@ 2022-08-24 2:51 llvm at rifkin dot dev
2022-08-24 3:06 ` [Bug middle-end/106727] " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: llvm at rifkin dot dev @ 2022-08-24 2:51 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106727
Bug ID: 106727
Summary: Missed fold / canonicalization for checking if a
number is a power of 2
Product: gcc
Version: 12.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: llvm at rifkin dot dev
Target Milestone: ---
These two are equivalent but generate different code:
bool foo(unsigned n) {
return std::popcount(n) <= 1;
}
bool bar(unsigned n) {
return (n & (n - 1)) == 0;
}
https://godbolt.org/z/crrxnfWo7
For systems that don't have popcount instructions it would be very beneficial
to transform foo -> bar. For systems that do have popcount instructions it
still would be beneficial to canonicalize the two.
^ permalink raw reply [flat|nested] 5+ messages in thread* [Bug middle-end/106727] Missed fold / canonicalization for checking if a number is a power of 2 2022-08-24 2:51 [Bug tree-optimization/106727] New: Missed fold / canonicalization for checking if a number is a power of 2 llvm at rifkin dot dev @ 2022-08-24 3:06 ` pinskia at gcc dot gnu.org 2022-08-24 7:21 ` rguenth at gcc dot gnu.org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2022-08-24 3:06 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106727 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Severity|normal |enhancement Component|tree-optimization |middle-end ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/106727] Missed fold / canonicalization for checking if a number is a power of 2 2022-08-24 2:51 [Bug tree-optimization/106727] New: Missed fold / canonicalization for checking if a number is a power of 2 llvm at rifkin dot dev 2022-08-24 3:06 ` [Bug middle-end/106727] " pinskia at gcc dot gnu.org @ 2022-08-24 7:21 ` rguenth at gcc dot gnu.org 2024-03-04 22:57 ` pinskia at gcc dot gnu.org 2024-03-04 22:58 ` pinskia at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: rguenth at gcc dot gnu.org @ 2022-08-24 7:21 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106727 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |missed-optimization Status|UNCONFIRMED |NEW Ever confirmed|0 |1 Last reconfirmed| |2022-08-24 --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- Confirmed. Expanding __builtin_popcount (n) <= 1 as (n & (n - 1)) == 0 might be already done. The canonicalization could be applied if .POPCOUNT is available. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/106727] Missed fold / canonicalization for checking if a number is a power of 2 2022-08-24 2:51 [Bug tree-optimization/106727] New: Missed fold / canonicalization for checking if a number is a power of 2 llvm at rifkin dot dev 2022-08-24 3:06 ` [Bug middle-end/106727] " pinskia at gcc dot gnu.org 2022-08-24 7:21 ` rguenth at gcc dot gnu.org @ 2024-03-04 22:57 ` pinskia at gcc dot gnu.org 2024-03-04 22:58 ` pinskia at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2024-03-04 22:57 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106727 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 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Mine. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/106727] Missed fold / canonicalization for checking if a number is a power of 2 2022-08-24 2:51 [Bug tree-optimization/106727] New: Missed fold / canonicalization for checking if a number is a power of 2 llvm at rifkin dot dev ` (2 preceding siblings ...) 2024-03-04 22:57 ` pinskia at gcc dot gnu.org @ 2024-03-04 22:58 ` pinskia at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2024-03-04 22:58 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106727 --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- (In reply to Richard Biener from comment #1) > Confirmed. Expanding __builtin_popcount (n) <= 1 as (n & (n - 1)) == 0 > might be already done. The canonicalization could be applied if .POPCOUNT > is available. No, it is not already done, expanding `__builtin_popcount (n) == 1` is done (and including if n is known not to include 0 which is exapnded as `n & (n - 1) == 0`) ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-03-04 22:58 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-08-24 2:51 [Bug tree-optimization/106727] New: Missed fold / canonicalization for checking if a number is a power of 2 llvm at rifkin dot dev 2022-08-24 3:06 ` [Bug middle-end/106727] " pinskia at gcc dot gnu.org 2022-08-24 7:21 ` rguenth at gcc dot gnu.org 2024-03-04 22:57 ` pinskia at gcc dot gnu.org 2024-03-04 22:58 ` pinskia at gcc dot gnu.org
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