[MemCpyOpt] The store instruction should not be removed by DSE.

[dianqk]

This IR is reduced from rust-lang/rust#116976.

declare void @f_byval(ptr byval(i32))
declare void @llvm.memcpy.p0.p0.i64(ptr, ptr, i64, i1)

define void @byval_param_noalias_metadata(ptr align 4 byval(i32) %ptr) {
  %tmp = alloca i32, align 4
  store i32 1, ptr %ptr, !noalias !2
  call void @llvm.memcpy.p0.p0.i64(ptr align 4 %tmp, ptr align 4 %ptr, i64 4, i1 false)
  call void @f_byval(ptr align 4 byval(i32) %tmp), !alias.scope !2
  ret void
}

!0 = !{!0}
!1 = !{!1, !0}
!2 = !{!1}

The DSE removed the store instruction because MemCpyOpt did not update the alias information.

declare void @f_byval(ptr byval(i32))

declare void @llvm.memcpy.p0.p0.i64(ptr noalias nocapture writeonly, ptr noalias nocapture readonly, i64, i1 immarg) #0

define void @byval_param_noalias_metadata(ptr byval(i32) align 4 %ptr) {
  call void @f_byval(ptr byval(i32) align 4 %ptr), !alias.scope !0
  ret void
}

attributes #0 = { nocallback nofree nounwind willreturn memory(argmem: readwrite) }

!0 = !{!1}
!1 = distinct !{!1, !2}
!2 = distinct !{!2}

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

Similar to #67539.

[dianqk]

/cherry-pick 0c4f326

[llvmbot]

/branch llvm/llvm-project-release-prs/issue70578

[llvmbot]

/pull-request llvm/llvm-project-release-prs#757