http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60165
Bug ID: 60165 Summary: "may be used uninitialized" warning with -O3 but not with -O2 Product: gcc Version: 4.9.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: vincent-gcc at vinc17 dot net With: gcc (Debian 20140111-1) 4.9.0 20140111 (experimental) [trunk revision 206552] I get the following inconsistency in the warnings: ypig% cat out.i int a, b; int fn2 (int, int); int fn1 (int *p1) { if (fn2 (a, 0)) *p1 = b; int c; fn1 (&c); return c; } ypig% gcc-snapshot -c -Wall -Werror=maybe-uninitialized -O2 out.i ypig% gcc-snapshot -c -Wall -Werror=maybe-uninitialized -O3 out.i out.i: In function 'fn1': out.i:9:5: error: 'c' may be used uninitialized in this function [-Werror=maybe-uninitialized] return c; ^ cc1: some warnings being treated as errors ypig% I don't know whether this is regarded as normal, but this looks strange. Note: I got this problem when compiling round_prec.c from the GNU MPFR trunk. I generated the preprocessed file with -E, then used creduce on the following script: #!/bin/sh { gcc-snapshot -c -Wall -Werror=maybe-uninitialized -O2 out.i && \ ! gcc-snapshot -c -Wall -Werror=maybe-uninitialized -O3 out.i } >/dev/null 2>&1 to generate the simple testcase (and fixed the declarations to avoid additional warnings -- I think I should have used -Werror in the script to avoid them in the first place).