See here: https://github.com/llvm/llvm-project/blob/master/llvm/lib/Target/X86/X86InterleavedAccess.cpp#L219

    Value *NewBasePtr =
        Builder.CreateGEP(VecBaseTy, VecBasePtr, Builder.getInt32(i));
    Instruction *NewLoad =
        Builder.CreateAlignedLoad(VecBaseTy, NewBasePtr, LI->getAlign());

Newly created loads inherit the original load's alignment. This is not correct, as the original load may have a larger alignment than the GEP done above.

A concrete failure we see is in: Transforms/InterleavedAccess/X86/interleavedLoad.ll

define <32 x i8> @interleaved_load_vf32_i8_stride3(* %ptr) {
  %wide.vec = load <96 x i8>, * %ptr, align 128
...
}
=>
define <32 x i8> @interleaved_load_vf32_i8_stride3(* %ptr) {
  %1 = bitcast * %ptr to *
  %2 = gep * %1, 16 x i32 0
  %3 = load <16 x i8>, * %2, align 128  ; <-- this is not 128-byte aligned
  %4 = gep * %1, 16 x i32 1
  %5 = load <16 x i8>, * %4, align 128
  %6 = gep * %1, 16 x i32 2
  %7 = load <16 x i8>, * %6, align 128
...
}


Report: https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=72296a443c683892&test=Transforms%2FInterleavedAccess%2FX86%2FinterleavedLoad.ll