Hi! The following testcase is miscompiled since r279392 aka r10-5451-gef29b12cfbb4979 The strlen pass has adjust_last_stmt function, which performs mainly strcat or strcat-like optimizations (say strcpy (x, "abcd"); strcat (x, p); or equivalent memcpy (x, "abcd", strlen ("abcd") + 1); char *q = strchr (x, 0); memcpy (x, p, strlen (p)); etc. where the first stmt stores '\0' character at the end but next immediately overwrites it and so the first memcpy can be adjusted to store 1 fewer bytes. handle_builtin_memcpy called this function in two spots, the first one guarded like: if (olddsi != NULL && tree_fits_uhwi_p (len) && !integer_zerop (len)) adjust_last_stmt (olddsi, stmt, false); i.e. only for constant non-zero length. The other spot can call it even for non-constant length but in that case we punt before that if that length isn't length of some string + 1, so again non-zero. The r279392 change I assume wanted to add some warning stuff and changed it like if (olddsi != NULL - && tree_fits_uhwi_p (len) && !integer_zerop (len)) - adjust_last_stmt (olddsi, stmt, false); + { + maybe_warn_overflow (stmt, len, rvals, olddsi, false, true); + adjust_last_stmt (olddsi, stmt, false); + } While maybe_warn_overflow possibly handles non-constant length fine, adjust_last_stmt really relies on length to be non-zero, which !integer_zerop (len) alone doesn't guarantee. While we could for len being SSA_NAME ask the ranger or tree_expr_nonzero_p, I think adjust_last_stmt will not benefit from it much, so the following patch just restores the above condition/previous behavior for the adjust_last_stmt call only.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2023-08-30 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/110914 * tree-ssa-strlen.cc (strlen_pass::handle_builtin_memcpy): Don't call adjust_last_stmt unless len is known constant. * gcc.c-torture/execute/pr110914.c: New test. --- gcc/tree-ssa-strlen.cc.jj 2023-04-27 10:17:46.406486796 +0200 +++ gcc/tree-ssa-strlen.cc 2023-08-29 18:13:38.189327203 +0200 @@ -3340,7 +3340,8 @@ strlen_pass::handle_builtin_memcpy (buil && !integer_zerop (len)) { maybe_warn_overflow (stmt, false, len, olddsi, false, true); - adjust_last_stmt (olddsi, stmt, false); + if (tree_fits_uhwi_p (len)) + adjust_last_stmt (olddsi, stmt, false); } int idx = get_stridx (src, stmt); --- gcc/testsuite/gcc.c-torture/execute/pr110914.c.jj 2023-08-29 18:38:33.305699206 +0200 +++ gcc/testsuite/gcc.c-torture/execute/pr110914.c 2023-08-29 18:38:18.678901007 +0200 @@ -0,0 +1,22 @@ +/* PR tree-optimization/110914 */ + +__attribute__ ((noipa)) int +foo (const char *s, unsigned long l) +{ + unsigned char r = 0; + __builtin_memcpy (&r, s, l != 0); + return r; +} + +int +main () +{ + const char *p = "123456"; + int a = foo (p, __builtin_strlen (p) - 5); + int b = foo (p, __builtin_strlen (p) - 6); + if (a != '1') + __builtin_abort (); + if (b != 0) + __builtin_abort (); + return 0; +} Jakub