https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104308
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by David Malcolm <dmalc...@gcc.gnu.org>: https://gcc.gnu.org/g:875342766d42988fa2f8eb7d34ef562ba69e340a commit r12-7856-g875342766d42988fa2f8eb7d34ef562ba69e340a Author: David Malcolm <dmalc...@redhat.com> Date: Mon Mar 28 09:43:07 2022 -0400 gimple-fold: fix location of loads for memory ops [PR104308] PR analyzer/104308 reports that when -Wanalyzer-use-of-uninitialized-value complains about certain memmove operations where the source is uninitialized, the diagnostic uses UNKNOWN_LOCATION: In function 'main': cc1: warning: use of uninitialized value '*(short unsigned int *)&s + 1' [CWE-457] [-Wanalyzer-use-of-uninitialized-value] 'main': event 1 | |pr104308.c:5:8: | 5 | char s[5]; /* { dg-message "region created on stack here" } */ | | ^ | | | | | (1) region created on stack here | 'main': event 2 | |cc1: | (2): use of uninitialized value '*(short unsigned int *)&s + 1' here | The issue is that gimple_fold_builtin_memory_op converts a memmove to: _3 = MEM <unsigned short> [(char * {ref-all})_1]; MEM <unsigned short> [(char * {ref-all})&s] = _3; but only sets the location of the 2nd stmt, not the 1st. Fixed thusly, giving: pr104308.c: In function 'main': pr104308.c:6:3: warning: use of uninitialized value '*(short unsigned int *)&s + 1' [CWE-457] [-Wanalyzer-use-of-uninitialized-value] 6 | memmove(s, s + 1, 2); /* { dg-warning "use of uninitialized value" } */ | ^~~~~~~~~~~~~~~~~~~~ 'main': events 1-2 | | 5 | char s[5]; /* { dg-message "region created on stack here" } */ | | ^ | | | | | (1) region created on stack here | 6 | memmove(s, s + 1, 2); /* { dg-warning "use of uninitialized value" } */ | | ~~~~~~~~~~~~~~~~~~~~ | | | | | (2) use of uninitialized value '*(short unsigned int *)&s + 1' here | One side-effect of this change is a change in part of the output of gcc.dg/uninit-40.c from: uninit-40.c:47:3: warning: â*(long unsigned int *)(&u[1][0][0])â is used uninitialized [-Wuninitialized] 47 | __builtin_memcpy (&v[1], &u[1], sizeof (V)); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ uninit-40.c:45:5: note: â*(long unsigned int *)(&u[1][0][0])â was declared here 45 | V u[2], v[2]; | ^ to: uninit-40.c:47:3: warning: âuâ is used uninitialized [-Wuninitialized] 47 | __builtin_memcpy (&v[1], &u[1], sizeof (V)); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ uninit-40.c:45:5: note: âuâ declared here 45 | V u[2], v[2]; | ^ What's happening is that pass "early_uninit"(29)'s call to maybe_warn_operand is guarded by this condition: 1051 else if (gimple_assign_load_p (stmt) 1052 && gimple_has_location (stmt)) Before the patch, the stmt: _3 = MEM <unsigned long> [(char * {ref-all})&u + 8B]; has no location, and so early_uninit skips this operand at line 1052 above. Later, pass "uninit"(217) tests the var_decl "u$8", and emits a warning for it. With the patch, the stmt has a location, and so early_uninit emits a warning for "u" and sets a NW_UNINIT warning suppression at that location. Later, pass "uninit"(217)'s test of "u$8" is rejected due to that per-location suppression of uninit warnings, from the earlier warning. gcc/ChangeLog: PR analyzer/104308 * gimple-fold.cc (gimple_fold_builtin_memory_op): When optimizing to loads then stores, set the location of the new load stmt. gcc/testsuite/ChangeLog: PR analyzer/104308 * gcc.dg/analyzer/pr104308.c: New test. * gcc.dg/uninit-40.c (foo): Update expression in expected message. Signed-off-by: David Malcolm <dmalc...@redhat.com>
