https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121190
--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Tamar Christina <tnfch...@gcc.gnu.org>: https://gcc.gnu.org/g:46a862ef08f3c44780c8d9043ce16382d8a70ada commit r16-2632-g46a862ef08f3c44780c8d9043ce16382d8a70ada Author: Pengfei Li <pengfei....@arm.com> Date: Wed Jul 30 10:51:11 2025 +0100 vect: Fix insufficient alignment requirement for speculative loads [PR121190] This patch fixes a segmentation fault issue that can occur in vectorized loops with an early break. When GCC vectorizes such loops, it may insert a versioning check to ensure that data references (DRs) with speculative loads are aligned. The check normally requires DRs to be aligned to the vector mode size, which prevents generated vector load instructions from crossing page boundaries. However, this is not sufficient when a single scalar load is vectorized into multiple loads within the same iteration. In such cases, even if none of the vector loads crosses page boundaries, subsequent loads after the first one may still access memory beyond current valid page. Consider the following loop as an example: while (i < MAX_COMPARE) { if (*(p + i) != *(q + i)) return i; i++; } When compiled with "-O3 -march=znver2" on x86, the vectorized loop may include instructions like: vmovdqa (%rcx,%rax), %ymm0 vmovdqa 32(%rcx,%rax), %ymm1 vpcmpeqq (%rdx,%rax), %ymm0, %ymm0 vpcmpeqq 32(%rdx,%rax), %ymm1, %ymm1 Note two speculative vector loads are generated for each DR (p and q). The first vmovdqa and vpcmpeqq are safe due to the vector size (32-byte) alignment, but the following ones (at offset 32) may not be safe because they could read from the beginning of the next memory page, potentially leading to segmentation faults. To avoid the issue, this patch increases the alignment requirement for speculative loads to DR_TARGET_ALIGNMENT. It ensures all vector loads in the same vector iteration access memory within the same page. gcc/ChangeLog: PR tree-optimization/121190 * tree-vect-data-refs.cc (vect_enhance_data_refs_alignment): Increase alignment requirement for speculative loads. gcc/testsuite/ChangeLog: PR tree-optimization/121190 * gcc.dg/vect/vect-early-break_52.c: Update an unsafe test. * gcc.dg/vect/vect-early-break_137-pr121190.c: New test.
