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* [Bug c/98418] New: Valid integer constant expressions based on expressions that trigger -Wshift-overflow are treated as non-constants @ 2020-12-22 10:47 pskocik at gmail dot com 2020-12-22 10:50 ` [Bug c/98418] " pinskia at gcc dot gnu.org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: pskocik at gmail dot com @ 2020-12-22 10:47 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98418 Bug ID: 98418 Summary: Valid integer constant expressions based on expressions that trigger -Wshift-overflow are treated as non-constants Product: gcc Version: 6.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: pskocik at gmail dot com Target Milestone: --- This causes things like: struct foo { unsigned bit: (0xffffffffll<<40)!=0; }; to elicit a -pedantic warning about the bitfield width not being a proper integer constant expression, even though it is. In other contexts, a complete compilation error might ensue: extern int bar[ (0xffffffffll<<40)!=0 ]; //seen as an invalid VLA https://gcc.godbolt.org/z/7zfz96 Neither clang nor gcc <= 5 appear to have this bug. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93241 seems related. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/98418] Valid integer constant expressions based on expressions that trigger -Wshift-overflow are treated as non-constants 2020-12-22 10:47 [Bug c/98418] New: Valid integer constant expressions based on expressions that trigger -Wshift-overflow are treated as non-constants pskocik at gmail dot com @ 2020-12-22 10:50 ` pinskia at gcc dot gnu.org 2020-12-24 18:53 ` pskocik at gmail dot com 2020-12-24 18:55 ` pskocik at gmail dot com 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2020-12-22 10:50 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98418 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Shifting into the sign bit is problematic. I cant remember the exact rules. Using ull is valid though. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/98418] Valid integer constant expressions based on expressions that trigger -Wshift-overflow are treated as non-constants 2020-12-22 10:47 [Bug c/98418] New: Valid integer constant expressions based on expressions that trigger -Wshift-overflow are treated as non-constants pskocik at gmail dot com 2020-12-22 10:50 ` [Bug c/98418] " pinskia at gcc dot gnu.org @ 2020-12-24 18:53 ` pskocik at gmail dot com 2020-12-24 18:55 ` pskocik at gmail dot com 2 siblings, 0 replies; 4+ messages in thread From: pskocik at gmail dot com @ 2020-12-24 18:53 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98418 --- Comment #2 from pskocik at gmail dot com --- You're right. The bug was in my code. struct foo { unsigned bit: (0xffffffffll<<40)!=0; }; is indeed UB due to http://port70.net/~nsz/c/c11/n1570.html#6.5.7p4, but struct foo { unsigned bit: (0xffffffffull<<40)!=0; }; isn't and GCC accepts it without complaint. Apologies for the false alarm. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/98418] Valid integer constant expressions based on expressions that trigger -Wshift-overflow are treated as non-constants 2020-12-22 10:47 [Bug c/98418] New: Valid integer constant expressions based on expressions that trigger -Wshift-overflow are treated as non-constants pskocik at gmail dot com 2020-12-22 10:50 ` [Bug c/98418] " pinskia at gcc dot gnu.org 2020-12-24 18:53 ` pskocik at gmail dot com @ 2020-12-24 18:55 ` pskocik at gmail dot com 2 siblings, 0 replies; 4+ messages in thread From: pskocik at gmail dot com @ 2020-12-24 18:55 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98418 pskocik at gmail dot com changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |INVALID --- Comment #3 from pskocik at gmail dot com --- You're right. The bug was in my code. struct foo { unsigned bit: (0xffffffffll<<40)!=0; }; is indeed UB due to http://port70.net/~nsz/c/c11/n1570.html#6.5.7p4, but struct foo { unsigned bit: (0xffffffffull<<40)!=0; }; isn't and GCC accepts it without complaint. Apologies for the false alarm. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-12-24 18:55 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2020-12-22 10:47 [Bug c/98418] New: Valid integer constant expressions based on expressions that trigger -Wshift-overflow are treated as non-constants pskocik at gmail dot com 2020-12-22 10:50 ` [Bug c/98418] " pinskia at gcc dot gnu.org 2020-12-24 18:53 ` pskocik at gmail dot com 2020-12-24 18:55 ` pskocik at gmail dot com
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