[llvm-bugs] [Bug 50589] New: [Inliner] Noalias metadata incorrectly added to simplified calls

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50589

            Bug ID: 50589
           Summary: [Inliner] Noalias metadata incorrectly added to
                    simplified calls
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Interprocedural Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: nikita.ppv at gmail.com
                CC: jeroen.dobbelaere at synopsys.com,
                    llvm-bugs at lists.llvm.org

>From https://reviews.llvm.org/D102110#inline-972360:

define <2 x i8> @callee(<2 x i8>* %ptr1, <2 x i8>* noalias %ptr2, <2 x i1>
%mask, <2 x i8> %passthru) {
  %ret = call <2 x i8> @llvm.masked.load.v2i8(<2 x i8>* %ptr1, i32 1, <2 x i1>
%mask, <2 x i8> %passthru)
  store <2 x i8> zeroinitializer, <2 x i8>* %ptr2
  ret <2 x i8> %ret
}

define void @caller(<2 x i8>* %ptr1, <2 x i8>* %ptr2) {
  %passthru = load <2 x i8>, <2 x i8>* %ptr2
  call <2 x i8> @callee(<2 x i8>* %ptr1, <2 x i8>* %ptr2, <2 x i1>
zeroinitializer, <2 x i8> %passthru)
  ret void
}

declare <2 x i8> @llvm.masked.load.v2i8(<2 x i8>*, i32, <2 x i1>, <2 x i8>)

Results in:

define <2 x i8> @callee(<2 x i8>* %ptr1, <2 x i8>* noalias %ptr2, <2 x i1>
%mask, <2 x i8> %passthru) {
  %ret = call <2 x i8> @llvm.masked.load.v2i8.p0v2i8(<2 x i8>* %ptr1, i32 1, <2
x i1> %mask, <2 x i8> %passthru)
  store <2 x i8> zeroinitializer, <2 x i8>* %ptr2, align 2
  ret <2 x i8> %ret
}

define void @caller(<2 x i8>* %ptr1, <2 x i8>* %ptr2) {
  %passthru = load <2 x i8>, <2 x i8>* %ptr2, align 2, !noalias !0
  call void @llvm.experimental.noalias.scope.decl(metadata !0)
  store <2 x i8> zeroinitializer, <2 x i8>* %ptr2, align 2, !alias.scope !0
  ret void
}

In this case, we don't even need the incorrect annotation to go on an
instruction from the caller, it can also happen with a callee instruction:

define <2 x i8> @callee(<2 x i8>* %ptr1, <2 x i8>* noalias %ptr2, <2 x i1>
%mask) {
  %passthru = load <2 x i8>, <2 x i8>* %ptr2
  %ret = call <2 x i8> @llvm.masked.load.v2i8(<2 x i8>* %ptr1, i32 1, <2 x i1>
%mask, <2 x i8> %passthru)
  store <2 x i8> zeroinitializer, <2 x i8>* %ptr2
  ret <2 x i8> %ret
}

define void @caller(<2 x i8>* %ptr1, <2 x i8>* %ptr2) {
  call <2 x i8> @callee(<2 x i8>* %ptr1, <2 x i8>* %ptr2, <2 x i1>
zeroinitializer)
  ret void
}

declare <2 x i8> @llvm.masked.load.v2i8(<2 x i8>*, i32, <2 x i1>, <2 x i8>)

Results in:

define <2 x i8> @callee(<2 x i8>* %ptr1, <2 x i8>* noalias %ptr2, <2 x i1>
%mask) {
  %passthru = load <2 x i8>, <2 x i8>* %ptr2, align 2
  %ret = call <2 x i8> @llvm.masked.load.v2i8.p0v2i8(<2 x i8>* %ptr1, i32 1, <2
x i1> %mask, <2 x i8> %passthru)
  store <2 x i8> zeroinitializer, <2 x i8>* %ptr2, align 2
  ret <2 x i8> %ret
}

define void @caller(<2 x i8>* %ptr1, <2 x i8>* %ptr2) {
  call void @llvm.experimental.noalias.scope.decl(metadata !0)
  %passthru.i = load <2 x i8>, <2 x i8>* %ptr2, align 2, !alias.scope !0,
!noalias !0
  store <2 x i8> zeroinitializer, <2 x i8>* %ptr2, align 2, !alias.scope !0
  ret void
}

Note how the metadata is claiming that the load does not alias ... with itself.

We should not be adding noalias metadata to instructions that are the result of
simplification, as they may not correspond to the instruction from the original
function.

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