https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113907
Jan Hubicka <hubicka at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Summary|[14 regression] ICU |[12/13/14 regression] ICU |miscompiled since on x86 |miscompiled since on x86 |since |since |r14-5109-ga291237b628f41 |r14-5109-ga291237b628f41 --- Comment #41 from Jan Hubicka <hubicka at gcc dot gnu.org> --- OK, the reason why this does not work is that ranger ignores earlier value ranges on everything but default defs and phis. // This is where the ranger picks up global info to seed initial // requests. It is a slightly restricted version of // get_range_global() above. // // The reason for the difference is that we can always pick the // default definition of an SSA with no adverse effects, but for other // SSAs, if we pick things up to early, we may prematurely eliminate // builtin_unreachables. // // Without this restriction, the test in g++.dg/tree-ssa/pr61034.C has // all of its unreachable calls removed too early. // // See discussion here: // https://gcc.gnu.org/pipermail/gcc-patches/2021-June/571709.html void gimple_range_global (vrange &r, tree name, struct function *fun) { tree type = TREE_TYPE (name); gcc_checking_assert (TREE_CODE (name) == SSA_NAME); if (SSA_NAME_IS_DEFAULT_DEF (name) || (fun && fun->after_inlining) || is_a<gphi *> (SSA_NAME_DEF_STMT (name))) { get_range_global (r, name, fun); return; } r.set_varying (type); } This makes ipa-prop to ignore earlier known value range and mask the bug. However adding PHI makes the problem to reproduce: #include <stdio.h> #include <stdlib.h> int data[100]; int c; static __attribute__((noinline)) int bar (int d, unsigned int d2) { if (d2 > 30) c++; return d + d2; } static int test2 (unsigned int i) { if (i > 100) __builtin_unreachable (); if (__builtin_expect (data[i] != 0, 1)) return data[i]; for (int j = 0; j < 100; j++) data[i] += bar (data[j], i&1 ? i+17 : i + 16); return data[i]; } static int test (unsigned int i) { if (i > 10) __builtin_unreachable (); if (__builtin_expect (data[i] != 0, 1)) return data[i]; for (int j = 0; j < 100; j++) data[i] += bar (data[j], i&1 ? i+17 : i + 16); return data[i]; } int main () { int ret = test (1) + test (2) + test (3) + test2 (4) + test2 (30); if (!c) abort (); return ret; } This fails with trunk, gcc12 and gcc13 and also with Jakub's patch.