https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126405
--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-16 branch has been updated by Kyrylo Tkachov <[email protected]>: https://gcc.gnu.org/g:3e5af3a489291ed5adba26132351ae6c59d6d629 commit r16-9425-g3e5af3a489291ed5adba26132351ae6c59d6d629 Author: Kyrylo Tkachov <[email protected]> Date: Sun Jul 26 01:48:55 2026 -0700 out-of-SSA: Use all partition names to find the decl to split [PR126405] split_overlapping_partition_decls gives every partition but one of a memory-resident VAR_DECL its own artificial decl, so that distinct stack slots do not end up sharing a MEM_EXPR. It takes the variable of a partition from that partition's representative. set_rtl attaches the base variable of any name in a partition to that partition's location, so the variable a partition is given need not be the one of its representative. Here the partition holding the loop-carried versions of an oversized vector temporary has an anonymous representative: Partition 1 (_2 - 2 14 16 ) _2 has no base variable, while 14 and 16 are g18_lsm.11_14 and _16 Partition 30 (g18_lsm.11_41 - 41 ) Partition 1 is skipped because SSA_NAME_VAR of _2 is null, so partition 30 believes it is the only partition of g18_lsm.11 and keeps the user decl. Both 128 byte slots then get MEM_EXPR g18_lsm.11. The load/store pair-fusion pass groups accesses by MEM_EXPR base and MEM_OFFSET, so it treated two stores that are 144 bytes apart as adjacent and fused them: before (set (mem:V4SI [sp+240]) (reg v17)) ; g18_lsm.11+96 (set (mem:V4SI [sp+384]) (reg v27)) ; g18_lsm.11+112 after (set (mem:V2x16QI [sp+240]) (unspec [(reg v17) (reg v27)] UNSPEC_STP)) [sp+384] is never written. Work out the variable each partition will be given and key the keep/split decision on that, reusing the function set_rtl makes the same choice with, renamed to expand_leader_merge now. That function keeps the variable it is given first unless a later one is DECL_IGNORED_P, and expansion hands set_rtl the representative before the other names, so the representative's variable goes in first. A partition holding names of two variables would otherwise be keyed on the wrong one. Bootstrapped and tested on aarch64-none-linux-gnu. gcc/ChangeLog: PR middle-end/126405 * cfgexpand.cc (leader_merge): Rename to... (expand_leader_merge): ...this. Make external. * cfgexpand.h (expand_leader_merge): Declare. * tree-outof-ssa.cc: Include cfgexpand.h. (split_overlapping_partition_decls): Determine the variable of a partition from all of its names. gcc/testsuite/ChangeLog: PR middle-end/126405 * gcc.c-torture/execute/pr126405.c: New test. * gcc.c-torture/execute/pr126405-2.c: New test. * gcc.dg/pr126405-1.c: New test. * gcc.dg/pr126405-2.c: New test. * gcc.dg/pr126405-3.c: New test. Signed-off-by: Kyrylo Tkachov <[email protected]> (cherry picked from commit 6f8fff34e8d854c3f66b2b7c9c64e973a71661cb)
