https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99395
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- So in the BB SLP attempt from loop vectorization (or in the BB SLP pass with -fno-predictive-commoning) we get confused during DR group building because of a duplicate access and fixup splitting the candidates at odd points. For the reduced testcase we see <bb 3> [local count: 1063004409]: # i_16 = PHI <_5(5), 0(2)> # ivtmp_18 = PHI <ivtmp_15(5), 511(2)> _1 = i_16 + 1; _2 = a[_1]; _3 = a[i_16]; _4 = _2 * _3; a[i_16] = _4; _5 = i_16 + 2; _6 = a[_5]; _7 = a[_1]; _8 = _6 * _7; a[_1] = _8; ivtmp_15 = ivtmp_18 - 1; if (ivtmp_15 != 0) goto <bb 5>; [99.00%] else goto <bb 4>; [1.00%] so a[_1] is loaded twice because CSE doesn't figure that a[i_16] cannot alias it. That causes us to split the load group.