[LoopVectorize] Missing noalias metadata on store

[nikic]

https://llvm.godbolt.org/z/jeT9a97P7

; RUN: opt -S -passes=loop-vectorize -mtriple=x86_64-unknown-linux-gnu
define void @test(ptr %base, i64 %len, ptr %scale.ptr) {
start:
  %len.idx = shl nuw nsw i64 %len, 3
  %end = getelementptr inbounds nuw i8, ptr %base, i64 %len.idx
  %_228 = icmp eq i64 %len, 0
  br i1 %_228, label %bb2, label %bb3.lr.ph

bb3.lr.ph:
  br label %bb3

bb3:
  %iter.sroa.0.09 = phi ptr [ %base, %bb3.lr.ph ], [ %_32, %bb3 ]
  %_32 = getelementptr inbounds nuw i8, ptr %iter.sroa.0.09, i64 8
  %_8 = load float, ptr %scale.ptr , align 4
  %2 = load float, ptr %iter.sroa.0.09, align 4
  %3 = fmul float %_8, %2
  store float %3, ptr %iter.sroa.0.09, align 4
  %_9 = load float, ptr %scale.ptr , align 4
  %4 = getelementptr inbounds nuw i8, ptr %iter.sroa.0.09, i64 4
  %5 = load float, ptr %4, align 4
  %6 = fmul float %_9, %5
  store float %6, ptr %4, align 4
  %_22 = icmp eq ptr %_32, %end
  br i1 %_22, label %bb2.loopexit, label %bb3

bb2.loopexit:
  br label %bb2

bb2:
  ret void
}

Generates a runtime check and this vector body:

vector.body:                                      ; preds = %vector.body, %vector.ph
  %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
  %offset.idx = mul i64 %index, 8
  %next.gep = getelementptr i8, ptr %base, i64 %offset.idx
  %9 = load float, ptr %scale.ptr, align 4, !alias.scope !0
  %broadcast.splatinsert = insertelement <2 x float> poison, float %9, i64 0
  %broadcast.splat = shufflevector <2 x float> %broadcast.splatinsert, <2 x float> poison, <2 x i32> zeroinitializer
  %wide.vec = load <4 x float>, ptr %next.gep, align 4
  %strided.vec = shufflevector <4 x float> %wide.vec, <4 x float> poison, <2 x i32> <i32 0, i32 2>
  %strided.vec2 = shufflevector <4 x float> %wide.vec, <4 x float> poison, <2 x i32> <i32 1, i32 3>
  %10 = fmul <2 x float> %broadcast.splat, %strided.vec
  %11 = load float, ptr %scale.ptr, align 4, !alias.scope !0
  %broadcast.splatinsert3 = insertelement <2 x float> poison, float %11, i64 0
  %broadcast.splat4 = shufflevector <2 x float> %broadcast.splatinsert3, <2 x float> poison, <2 x i32> zeroinitializer
  %12 = fmul <2 x float> %broadcast.splat4, %strided.vec2
  %13 = shufflevector <2 x float> %10, <2 x float> %12, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
  %interleaved.vec = shufflevector <4 x float> %13, <4 x float> poison, <4 x i32> <i32 0, i32 2, i32 1, i32 3>
  store <4 x float> %interleaved.vec, ptr %next.gep, align 4
  %index.next = add nuw i64 %index, 2
  %14 = icmp eq i64 %index.next, %n.vec
  br i1 %14, label %middle.block, label %vector.body, !llvm.loop !3

Note that there is !noalias metadata on the store, which means that the loads of the scaling factor cannot be LICMed.

The metadata is present if the initial loop only stores one value: https://llvm.godbolt.org/z/3Yrhna9je