https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125396
--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-16 branch has been updated by Andrea Pinski <[email protected]>: https://gcc.gnu.org/g:6933427282a2f1a22d0e967e16f41b419f83c11e commit r16-9412-g6933427282a2f1a22d0e967e16f41b419f83c11e Author: Andrew Pinski <[email protected]> Date: Wed May 20 13:20:15 2026 -0700 tree-cfgcleanup: Don't remove forwarder blocks (with phis) with phis that have abnormal uses [PR125396] This was a latent bug in the checks for removing of a forwarder block which has a phi. Take: <bb 15> [local count: 182536112]: # arr1$0_32 = PHI <arr1$0_36(ab)(11)> <bb 14> [local count: 206998870]: # arr1$0_43(ab) = PHI <arr1$0_25(ab)(13), 9(15)> # sj12_44(ab) = PHI <sj12_31(ab)(13), arr1$0_32(15)> f8 (); Here bb 15 predecessor is a normal edge. So when merging the forwarder bb 15 into bb14 we end up with: <bb 12> [local count: 206998870]: # arr1$0_42(ab) = PHI <arr1$0_24(ab)(11), 9(9)> # sj12_43(ab) = PHI <sj12_30(ab)(11), arr1$0_35(ab)(9)> f8 (); and now there is an overlap of live range of arr1$0_35 and arr1$0_42. So we need to reject the case where we have phis and the phi arguments that use abnormal uses. Changes since v1: * v2: Look at phi arguments of the forwarder block rather than the dest bb having an abnormal edge out. * v3: Fix bb_phis_references_abnormal_uses to use the gimple_phi_num_args to search over the phi arguments. Also fix the commit message which was wrong. Bootstrapped and tested on x86_64-linux-gnu. PR tree-optimization/125396 gcc/ChangeLog: * tree-cfgcleanup.cc (bb_phis_references_abnormal_uses): New function. (maybe_remove_forwarder_block): Check to make sure the forwarder block does not have a phi that references ssa name that has abnormal uses. gcc/testsuite/ChangeLog: * gcc.dg/torture/pr125396-1.c: New test. Signed-off-by: Andrew Pinski <[email protected]> (cherry picked from commit ec79b0779b6eeb9ef3b8a45f46a596cbb75a7844)
