https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112303
--- Comment #15 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:d5a3b4afcdf4d517334a2717dbb65ae0d2c26507 commit r14-9707-gd5a3b4afcdf4d517334a2717dbb65ae0d2c26507 Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Mar 28 15:00:44 2024 +0100 profile-count: Avoid overflows into uninitialized [PR112303] The testcase in the patch ICEs with --- gcc/tree-scalar-evolution.cc +++ gcc/tree-scalar-evolution.cc @@ -3881,7 +3881,7 @@ final_value_replacement_loop (class loop *loop) /* Propagate constants immediately, but leave an unused initialization around to avoid invalidating the SCEV cache. */ - if (CONSTANT_CLASS_P (def) && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rslt)) + if (0 && CONSTANT_CLASS_P (def) && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rslt)) replace_uses_by (rslt, def); /* Create the replacement statements. */ (the addition of the above made the ICE latent), because profile_count addition doesn't check for overflows and if unlucky, we can even overflow into the uninitialized value. Getting really huge profile counts is very easy even when not using recursive inlining in loops, e.g. __attribute__((noipa)) void bar (void) { __builtin_exit (0); } __attribute__((noipa)) void foo (void) { for (int i = 0; i < 1000; ++i) for (int j = 0; j < 1000; ++j) for (int k = 0; k < 1000; ++k) for (int l = 0; l < 1000; ++l) for (int m = 0; m < 1000; ++m) for (int n = 0; n < 1000; ++n) for (int o = 0; o < 1000; ++o) for (int p = 0; p < 1000; ++p) for (int q = 0; q < 1000; ++q) for (int r = 0; r < 1000; ++r) for (int s = 0; s < 1000; ++s) for (int t = 0; t < 1000; ++t) for (int u = 0; u < 1000; ++u) for (int v = 0; v < 1000; ++v) for (int w = 0; w < 1000; ++w) for (int x = 0; x < 1000; ++x) for (int y = 0; y < 1000; ++y) for (int z = 0; z < 1000; ++z) for (int a = 0; a < 1000; ++a) for (int b = 0; b < 1000; ++b) bar (); } int main () { foo (); } reaches the maximum count already on the 11th loop. Some other methods of profile_count like apply_scale already do use MIN (val, max_count) before assignment to m_val, this patch just extends that to operator{+,+=} methods. Furthermore, one overload of apply_probability wasn't using safe_scale_64bit and so could very easily overflow as well - prob is required to be [0, 10000] and if m_val is near the max_count, it can overflow even with multiplications by 8. 2024-03-28 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/112303 * profile-count.h (profile_count::operator+): Perform addition in uint64_t variable and set m_val to MIN of that val and max_count. (profile_count::operator+=): Likewise. (profile_count::operator-=): Formatting fix. (profile_count::apply_probability): Use safe_scale_64bit even in the int overload. * gcc.c-torture/compile/pr112303.c: New test.
