The reproducers for PR 63311, both Fortran and C (attachment 33852 [details]) currently generate false positives from -Wanalyzer-use-of-uninitialized-value when optimization is off (and they are silent when optimization is on). It seems to be an issue with -fanalyzer thinking that __builtin_sinf could clobber *flag (which presumably it can't, being pure or const), thus allowing for the "flag is false" branch to skip initialization of t and tt, and then later executing the "flag is true" branch.
Potentially just a dup of PR analyzer/104434, but there might be additional issues with the reproducer.
The master branch has been updated by David Malcolm <dmalcolm@gcc.gnu.org>: https://gcc.gnu.org/g:5fbcbcaff7248604e04b39464f4fbd64fbf6e43b commit r12-7270-g5fbcbcaff7248604e04b39464f4fbd64fbf6e43b Author: David Malcolm <dmalcolm@redhat.com> Date: Wed Feb 16 18:21:58 2022 -0500 analyzer: const functions have no side effects [PR104576] PR analyzer/104576 tracks that we issue a false positive from -Wanalyzer-use-of-uninitialized-value for the reproducers of PR 63311 when optimization is disabled. The root cause is that the analyzer was considering that a call to __builtin_sinf could have side-effects. This patch fixes things by generalizing the handling for "pure" functions to also consider "const" functions. gcc/analyzer/ChangeLog: PR analyzer/104576 * region-model.cc: Include "calls.h". (region_model::on_call_pre): Use flags_from_decl_or_type to generalize check for DECL_PURE_P to also check for ECF_CONST. gcc/testsuite/ChangeLog: PR analyzer/104576 * gcc.dg/analyzer/torture/uninit-pr63311.c: New test. * gcc.dg/analyzer/uninit-pr104576.c: New test. * gfortran.dg/analyzer/uninit-pr63311.f90: New test. Signed-off-by: David Malcolm <dmalcolm@redhat.com>
Should be fixed by the above patch. (In reply to David Malcolm from comment #1) > Potentially just a dup of PR analyzer/104434, but there might be additional > issues with the reproducer. Not quite: this one covers "const" functions not having side-effects, whereas PR analyzer/104434 concerns the return values of const/pure functions.