[Bug c/61409] New: [4.9 regression] -Wmaybe-uninitialized false-positive with -O2
eggert at gnu dot org
gcc-bugzilla@gcc.gnu.org
Wed Jun 4 07:40:00 GMT 2014
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61409
Bug ID: 61409
Summary: [4.9 regression] -Wmaybe-uninitialized false-positive
with -O2
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: eggert at gnu dot org
Created attachment 32887
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=32887&action=edit
sample program illustrating the false positive
GCC 4.9.0 x86-64. I do not observe the bug with GCC 4.8.2.
I discovered this bug when compiling GNU Emacs, and abstracted it into the
simplest test case I could easily generate. When I compile the attached
program g.i with the command:
gcc -Wmaybe-uninitialized -O2 -c g.i
GCC warns:
g.i:607:21: warning: 'mw' may be used uninitialized in this function
[-Wmaybe-uninitialized]
mw->pixel_top = rw->pixel_height;
But mw cannot possibly be uninitialized here. Also, mw was used in the
previous line, with no warning.
The bug may be related to lines 602 and 603, which are long and which do not
mention mw, as removing these lines makes the diagnostic go away.
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