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* [Bug tree-optimization/103633] New: Missed popcount recognition
@ 2021-12-09 15:29 acoplan at gcc dot gnu.org
2021-12-09 15:42 ` [Bug tree-optimization/103633] " pinskia at gcc dot gnu.org
2022-10-10 18:10 ` pinskia at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: acoplan at gcc dot gnu.org @ 2021-12-09 15:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103633
Bug ID: 103633
Summary: Missed popcount recognition
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: acoplan at gcc dot gnu.org
Target Milestone: ---
For:
int f1 (unsigned long b) {
int c = 0;
while (b) {
b &= b - 1;
c++;
}
return c;
}
int f2(unsigned long x) {
int c = 0;
for (; x; x >>= 1) {
if (x & 1)
c++;
}
return c;
}
GCC recognizes f1 as popcount but not the more naive f2.
^ permalink raw reply [flat|nested] 3+ messages in thread* [Bug tree-optimization/103633] Missed popcount recognition 2021-12-09 15:29 [Bug tree-optimization/103633] New: Missed popcount recognition acoplan at gcc dot gnu.org @ 2021-12-09 15:42 ` pinskia at gcc dot gnu.org 2022-10-10 18:10 ` pinskia at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-12-09 15:42 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103633 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |pinskia at gcc dot gnu.org Last reconfirmed| |2021-12-09 Severity|normal |enhancement Ever confirmed|0 |1 Status|UNCONFIRMED |NEW --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- We don't recongize this either: int f21(unsigned long x) { int c = 0; for (; x; x >>= 1) { c+= (x & 1); } return c; } Confirmed. ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/103633] Missed popcount recognition 2021-12-09 15:29 [Bug tree-optimization/103633] New: Missed popcount recognition acoplan at gcc dot gnu.org 2021-12-09 15:42 ` [Bug tree-optimization/103633] " pinskia at gcc dot gnu.org @ 2022-10-10 18:10 ` pinskia at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: pinskia at gcc dot gnu.org @ 2022-10-10 18:10 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103633 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- A few extra testcase: ``` unsigned short fs(unsigned int execs) { unsigned i; unsigned short num_algorithms = 0; for (i=0; i<32; i++) { if ((1<<i) & execs) num_algorithms++; } return num_algorithms; } unsigned short fi(unsigned int execs) { unsigned i; unsigned int num_algorithms = 0; for (i=0; i<32; i++) { if ((1<<i) & execs) num_algorithms++; } return num_algorithms; } ``` These testcases comes from coremarks but from the startup code so it has no performance impact ... You will also notice that fi has better code gen than fs with the vectorizer. ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-10-10 18:10 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-12-09 15:29 [Bug tree-optimization/103633] New: Missed popcount recognition acoplan at gcc dot gnu.org 2021-12-09 15:42 ` [Bug tree-optimization/103633] " pinskia at gcc dot gnu.org 2022-10-10 18:10 ` pinskia at gcc dot gnu.org
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