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* [Bug middle-end/112382] New: `(a&b) != a` where a is known to have one known bit set is not optimized to ((~b&a)>>shift) & 1 @ 2023-11-04 21:09 pinskia at gcc dot gnu.org 2023-11-06 8:11 ` [Bug middle-end/112382] " rguenth at gcc dot gnu.org 2023-11-07 3:34 ` pinskia at gcc dot gnu.org 0 siblings, 2 replies; 3+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-11-04 21:09 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112382 Bug ID: 112382 Summary: `(a&b) != a` where a is known to have one known bit set is not optimized to ((~b&a)>>shift) & 1 Product: gcc Version: 14.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: enhancement Priority: P3 Component: middle-end Assignee: unassigned at gcc dot gnu.org Reporter: pinskia at gcc dot gnu.org Target Milestone: --- Take: ``` int f(int a, int b) { a &= 0x10; return (a&b) < a; } int f1(unsigned a, unsigned b) { a &= 0x10; return (a&b) != a; } int f2(unsigned a, unsigned b) { a &= 0x10; unsigned c = (a&b) ^ a; return c>>4; } int f3(unsigned a, unsigned b) { unsigned c = (~b)&a; return (c>>4) & 1; } ``` These all should produce the same code. Right now f2 and f3 produce the best code on x86 (especially with BMI enabled) and aarch64 note f to f1 is really PR 112093 . ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug middle-end/112382] `(a&b) != a` where a is known to have one known bit set is not optimized to ((~b&a)>>shift) & 1 2023-11-04 21:09 [Bug middle-end/112382] New: `(a&b) != a` where a is known to have one known bit set is not optimized to ((~b&a)>>shift) & 1 pinskia at gcc dot gnu.org @ 2023-11-06 8:11 ` rguenth at gcc dot gnu.org 2023-11-07 3:34 ` pinskia at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: rguenth at gcc dot gnu.org @ 2023-11-06 8:11 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112382 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Target| |x86_64-*-* --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- Note ((~b&a)>>shift) & 1 is two more GIMPLE ops than (a&b) != a so I'd expect the reverse transform on GIMPLE and maybe target specific expansion tweaks (or combine at work). Mangling the testcases to expect CSE with the (a&b) != a would be the thing to test on GIMPLE (maybe simply expect ICF to happen?!) ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug middle-end/112382] `(a&b) != a` where a is known to have one known bit set is not optimized to ((~b&a)>>shift) & 1 2023-11-04 21:09 [Bug middle-end/112382] New: `(a&b) != a` where a is known to have one known bit set is not optimized to ((~b&a)>>shift) & 1 pinskia at gcc dot gnu.org 2023-11-06 8:11 ` [Bug middle-end/112382] " rguenth at gcc dot gnu.org @ 2023-11-07 3:34 ` pinskia at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-11-07 3:34 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112382 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- (In reply to Richard Biener from comment #1) > Note ((~b&a)>>shift) & 1 is two more GIMPLE ops than (a&b) != a so I'd > expect the reverse transform on GIMPLE and maybe target specific expansion > tweaks (or combine at work). Right, that is why I put the component as middle-end. Specifically because I think `(a&b) != a` should be the Canonical form and only expanded either in isel or expand . ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2023-11-07 3:34 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-11-04 21:09 [Bug middle-end/112382] New: `(a&b) != a` where a is known to have one known bit set is not optimized to ((~b&a)>>shift) & 1 pinskia at gcc dot gnu.org 2023-11-06 8:11 ` [Bug middle-end/112382] " rguenth at gcc dot gnu.org 2023-11-07 3:34 ` pinskia at gcc dot gnu.org
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