Created attachment 54425 [details] Reduced reproducer Trunk shows many (dozens?) of -Wanalyzer-use-of-uninitialized-value false positives on qemu's softfloat.c https://godbolt.org/z/MTe9597Eh shows: <source>: In function 'test': <source>:27:9: warning: use of uninitialized value 'fp0' [CWE-457] [-Wanalyzer-use-of-uninitialized-value] 27 | fp0 = floatx80_add(fp0, float32_to_floatx80((0x3F800000))); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 'test': events 1-3 | | 24 | floatx80 fp0; | | ^~~ | | | | | (1) region created on stack here | | (2) capacity: 16 bytes |...... | 27 | fp0 = floatx80_add(fp0, float32_to_floatx80((0x3F800000))); | | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | | | | | (3) use of uninitialized value 'fp0' here | Compiler returned: 0 where fp0 appears to have been initialized on the line above.
Doesn't seem to affect gcc 12.2 so marking as a regression.
Adding -fno-analyzer-state-purge fixes the false positive, looks like it's erroneously pruning the value of fp0 immediately after the first assignment.
The master branch has been updated by David Malcolm <dmalcolm@gcc.gnu.org>: https://gcc.gnu.org/g:77bb54b1b07add45007c664724b726541d672ef3 commit r13-5745-g77bb54b1b07add45007c664724b726541d672ef3 Author: David Malcolm <dmalcolm@redhat.com> Date: Wed Feb 8 13:47:36 2023 -0500 analyzer: fix overzealous state purging with on-stack structs [PR108704] PR analyzer/108704 reports many false positives seen from -Wanalyzer-use-of-uninitialized-value on qemu's softfloat.c on code like the following: struct st s; s = foo (); s = bar (s); // bogusly reports that s is uninitialized here where e.g. "struct st" is "floatx80" in the qemu examples. The root cause is overzealous purging of on-stack structs in the code I added in r12-7718-gfaacafd2306ad7, where at: s = bar (s); state_purge_per_decl::process_point_backwards "sees" the assignment to 's' and stops processing, effectively treating 's' as unneeded before this stmt, not noticing the use of 's' in the argument. Fixed thusly. The patch greatly reduces the number of -Wanalyzer-use-of-uninitialized-value warnings from my integration tests: ImageMagick-7.1.0-57: 10 -> 6 (-4) qemu-7.2: 858 -> 87 (-771) haproxy-2.7.1: 1 -> 0 (-1) All of the above that I've examined appear to be false positives. gcc/analyzer/ChangeLog: PR analyzer/108704 * state-purge.cc (state_purge_per_decl::process_point_backwards): Don't stop processing the decl if it's fully overwritten by this stmt if it's also used by this stmt. gcc/testsuite/ChangeLog: PR analyzer/108704 * gcc.dg/analyzer/uninit-7.c: New test. * gcc.dg/analyzer/uninit-pr108704.c: New test. Signed-off-by: David Malcolm <dmalcolm@redhat.com>
Should be fixed on trunk for GCC 13 by the above commit. I introduced the bug in r12-7718-gfaacafd2306ad7 so in theory it affects GCC 12 as well, but I haven't been able to reproduce it there. The bug is probably present there but latent, so I'm keeping this bug open to track backporting the fix to the gcc 12 branch.
The releases/gcc-12 branch has been updated by David Malcolm <dmalcolm@gcc.gnu.org>: https://gcc.gnu.org/g:5da2126c4df8d83c2b2f9de7bb393ab4f5832840 commit r12-9364-g5da2126c4df8d83c2b2f9de7bb393ab4f5832840 Author: David Malcolm <dmalcolm@redhat.com> Date: Wed Mar 29 14:16:48 2023 -0400 analyzer: fix overzealous state purging with on-stack structs [PR108704] PR analyzer/108704 reports many false positives seen from -Wanalyzer-use-of-uninitialized-value on qemu's softfloat.c on code like the following: struct st s; s = foo (); s = bar (s); // bogusly reports that s is uninitialized here where e.g. "struct st" is "floatx80" in the qemu examples. The root cause is overzealous purging of on-stack structs in the code I added in r12-7718-gfaacafd2306ad7, where at: s = bar (s); state_purge_per_decl::process_point_backwards "sees" the assignment to 's' and stops processing, effectively treating 's' as unneeded before this stmt, not noticing the use of 's' in the argument. Fixed thusly. The patch greatly reduces the number of -Wanalyzer-use-of-uninitialized-value warnings from my integration tests: ImageMagick-7.1.0-57: 10 -> 6 (-4) qemu-7.2: 858 -> 87 (-771) haproxy-2.7.1: 1 -> 0 (-1) All of the above that I've examined appear to be false positives. Cherrypicked from r13-5745-g77bb54b1b07add. gcc/analyzer/ChangeLog: PR analyzer/108704 * state-purge.cc (state_purge_per_decl::process_point_backwards): Don't stop processing the decl if it's fully overwritten by this stmt if it's also used by this stmt. gcc/testsuite/ChangeLog: PR analyzer/108704 * gcc.dg/analyzer/uninit-7.c: New test. * gcc.dg/analyzer/uninit-pr108704.c: New test. Signed-off-by: David Malcolm <dmalcolm@redhat.com>
Should be fixed on gcc 12 branch by the above (for the eventual gcc 12.3 release); marking as resolved.