public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
* [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
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).