Assume there is a directory "foo" in the current directory and there is a foo.c in ./foo , I saw this on 4.5.1
$ gcc-4.5 -fdump-tree-optimized -save-temps=obj foo/foo.c -S -o foo/foo.s foo/foo.c: In function foo: foo/foo.c:1:6: error: could not open dump file foo/foo/foo.140t.optimized: No such file or directory -- Summary: -save-temps=obj does not work correctly Product: gcc Version: 4.6.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: driver AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: jiez at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45163