https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124037
--- Comment #9 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Victor Do Nascimento <[email protected]>: https://gcc.gnu.org/g:4a30b45ffe3cb4ad2e35d73f1714f1a80e32edd7 commit r16-7915-g4a30b45ffe3cb4ad2e35d73f1714f1a80e32edd7 Author: Victor Do Nascimento <[email protected]> Date: Tue Feb 10 16:36:31 2026 +0000 vect: fix vectorization of non-gather elementwise loads [PR124037] For the vectorization of non-contiguous memory accesses such as the vectorization of loads from a particular struct member, specifically when vectorizing with unknown bounds (thus using a pointer and not an array) it is observed that inadequate alignment checking allows for the crossing of a page boundary within a single vectorized loop iteration. This leads to potential segmentation faults in the resulting binaries. For example, for the given datatype: typedef struct { uint64_t a; uint64_t b; uint32_t flag; uint32_t pad; } Data; and a loop such as: int foo (Data *ptr) { if (ptr == NULL) return -1; int cnt; for (cnt = 0; cnt < MAX; cnt++) { if (ptr->flag == 0) break; ptr++; } return cnt; } the vectorizer yields the following cfg on armhf: <bb 1>: _41 = ptr_4(D) + 16; <bb 2>: _44 = MEM[(unsigned int *)ivtmp_42]; ivtmp_45 = ivtmp_42 + 24; _46 = MEM[(unsigned int *)ivtmp_45]; ivtmp_47 = ivtmp_45 + 24; _48 = MEM[(unsigned int *)ivtmp_47]; ivtmp_49 = ivtmp_47 + 24; _50 = MEM[(unsigned int *)ivtmp_49]; vect_cst__51 = {_44, _46, _48, _50}; mask_patt_6.17_52 = vect_cst__51 == { 0, 0, 0, 0 }; if (mask_patt_6.17_52 != { 0, 0, 0, 0 }) goto <bb 4>; else ivtmp_43 = ivtmp_42 + 96; goto <bb 2>; <bb4> ... without any proper address alignment checks on the starting address or on whether alignment is preserved across iterations. We therefore fix the handling of such cases. To correct this, we modify the logic in `get_load_store_type', particularly the logic responsible for ensuring we don't read more than the scalar code would in the context of early breaks, extending it from handling not only gather-scatter and strided SLP accesses but also allowing it to properly handle element-wise accesses, wherein we specify that these need correct block alignment, thus promoting their `alignment_support_scheme' from `dr_unaligned_supported' to `dr_aligned'. gcc/ChangeLog: PR tree-optimization/124037 * tree-vect-stmts.cc (get_load_store_type): Fix alignment_support_scheme categorization for early break VMAT_ELEMENTWISE accesses. gcc/testsuite/ChangeLog: * gcc.dg/vect/vect-pr124037.c: New. * g++.dg/vect/vect-pr124037.cc: New.
