https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95794
Bug ID: 95794 Summary: strnlen of a constant string plus variable offset not folded when bound exceeds size Product: gcc Version: 10.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end Assignee: unassigned at gcc dot gnu.org Reporter: msebor at gcc dot gnu.org Target Milestone: --- GCC folds comparisons of the results of calls to strlen with constant strings and variable offsets but it doesn't do the same for the equivalent strnlen with a bound in excess of the string size (strnlen with a bound greater than the string length are equivalent to strlen with the same argument). $ cat z.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout z.c const char a[] = "12345"; void f (int i) { if (__builtin_strlen (&a[i]) > 5) // folded to false __builtin_abort (); } void g (int i) { if (__builtin_strnlen (&a[i], 7) > 5) // not folded __builtin_abort (); } ;; Function f (f, funcdef_no=0, decl_uid=1931, cgraph_uid=1, symbol_order=1) f (int i) { <bb 2> [local count: 1073741824]: return; } ;; Function g (g, funcdef_no=1, decl_uid=1934, cgraph_uid=2, symbol_order=2) g (int i) { const char * _1; long unsigned int _2; sizetype _6; <bb 2> [local count: 1073741824]: _6 = (sizetype) i_3(D); _1 = &a + _6; _2 = __builtin_strnlen (_1, 7); if (_2 > 5) goto <bb 3>; [0.00%] else goto <bb 4>; [100.00%] <bb 3> [count: 0]: __builtin_abort (); <bb 4> [local count: 1073741824]: return; }