Bug 87203 - Optimize x % constant ==/!= 0
Summary: Optimize x % constant ==/!= 0
Status: RESOLVED DUPLICATE of bug 82853
Alias: None
Product: gcc
Classification: Unclassified
Component: middle-end (show other bugs)
Version: 9.0
: P3 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
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Reported: 2018-09-03 11:06 UTC by Jakub Jelinek
Modified: 2018-09-03 11:38 UTC (History)
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Description Jakub Jelinek 2018-09-03 11:06:45 UTC 
As mentioned in http://duriansoftware.com/joe/Optimizing-is-multiple-checks-with-modular-arithmetic.html , we could optimize unsigned
x % const == 0
or
x % const != 0
into a single (non-highpart) multiplication plus comparison (at least for odd const, for even const we can rotate before comparison if target has cheap rotates, or could test low bits and compare).
Obviously, for power of two const we already emit the best code.
Comment 1 Marc Glisse 2018-09-03 11:31:46 UTC 
Dup of PR 82853 ?
Comment 2 Jakub Jelinek 2018-09-03 11:38:23 UTC 
Dup indeed.

*** This bug has been marked as a duplicate of bug 82853 ***