https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118107
Bug ID: 118107
Summary: false warning: "${inactive union member} may be used
uninitialized" (in constructor call activating
another, empty struct member, as union member)
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: giel+gcc at mortis dot eu
Target Milestone: ---
Created attachment 59909
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=59909&action=edit
reproduction scenario
Attached I have a completely cut down example that triggers a false positive
warning "X may be uninitialized". Also the same on compiler explorer:
https://godbolt.org/z/ErWaT5KMq
It only happens with -O1 *and* -fsanitize=undefined (but *not*
-fsanitize=undefined,address) (and -Wall -Wextra of course). When increasing
code size it needs -O2 at least to trigger.
The warning triggers on a call to the default constructor. Which activates an
*empty struct* as a union member. But the warning complains about the
*inactive* (non-empty) union member (maybe) being used uninitialized.
