https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78081
Bug ID: 78081
Summary: -Wmaybe-initialized false-alarm regression for Emacs
regex.c
Product: gcc
Version: 6.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: eggert at gnu dot org
Target Milestone: ---
Created attachment 39869
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39869&action=edit
test program illustrating -Wmaybe-uninitialized false alarm
I found this when compiling a test version of GNU Emacs with gcc (GCC) 6.2.1
20160916 (Red Hat 6.2.1-2) on x86-64. The problem does not occur with gcc (GCC)
4.8.5 20150623 (Red Hat 4.8.5-4) on x86-64 so this appears to be a regression.
The problem caused the Emacs build to fail when configured with
--enable-gcc-warnings, when compiling src/regex.c. I reduced the problem case
to a relatively small source file u2.i (attached). Compile it with the command:
gcc -S -Werror=maybe-uninitialized -O2 u2.i
GCC will complain as follows and then fail:
u2.i: In function 're_search_2':
u2.i:59:42: error: 'offset2' may be used uninitialized in this function
[-Werro\
r=maybe-uninitialized]
if (string2) string2 = offset2 + new_base;
~~~~~~~~^~~~~~~~~~
This diagnostic is incorrect, as offset2 must be initialized, using the same
reasoning that offset1 must be initialized (which GCC gets right).
