https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110603
--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:b338fdbc2b74f25c07da263a1f5983421fac1a53 commit r14-8487-gb338fdbc2b74f25c07da263a1f5983421fac1a53 Author: Jakub Jelinek <ja...@redhat.com> Date: Mon Jan 29 10:20:32 2024 +0100 tree-ssa-strlen: Fix pdata->maxlen computation [PR110603] On the following testcase we emit an invalid range of [2, 1] due to UB in the source. Older VRP code silently swapped the boundaries and made [1, 2] range out of it, but newer code just ICEs on it. The reason for pdata->minlen 2 is that we see a memcpy in this case setting both elements of the array to non-zero value, so strlen (a) can't be smaller than 2. The reason for pdata->maxlen 1 is that in char a[2] array without UB there can be at most 1 non-zero character because there needs to be '\0' termination in the buffer too. IMHO we shouldn't create invalid ranges like that and even creating for that case a range [1, 2] looks wrong to me, so the following patch just doesn't set maxlen in that case to the array size - 1, matching what will really happen at runtime when triggering such UB (strlen will be at least 2, perhaps more or will crash). This is what the second hunk of the patch does. The first hunk fixes a fortunately harmless thinko. If the strlen pass knows the string length (i.e. get_string_length function returns non-NULL), we take a different path, we get to this only if all we know is that there are certain number of non-zero characters but we don't know what it is followed with, whether further non-zero characters or zero termination or either of that. If we know exactly how many non-zero characters it is, such as char a[42]; ... memcpy (a, "01234567890123456789", 20); then we take an earlier if for the INTEGER_CST case and set correctly just pdata->minlen to 20 in that case, but if we have something like int len; ... if (len < 15 || len > 32) return; memcpy (a, "0123456789012345678901234567890123456789", len); then we have [15, 32] range for the nonzero_chars and we set pdata->minlen correctly to 15, but incorrectly set also pdata->maxlen to 32. That is not what the above implies, it just means that in some cases we know that there are at least 32 non-zero characters, followed by something we don't know. There is no guarantee that there is '\0' right after it, so it means nothing. The reason this is harmless, just confusing, is that the code a few lines later fortunately overwrites this incorrect pdata->maxlen value with something different (either array length - 1 or all ones etc.). 2024-01-29 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/110603 * tree-ssa-strlen.cc (get_range_strlen_dynamic): Remove incorrect setting of pdata->maxlen to vr.upper_bound (which is unconditionally overwritten anyway). Avoid creating invalid range with minlen larger than maxlen. Formatting fix. * gcc.c-torture/compile/pr110603.c: New test.
