[PhaseOrdering] Add test for PR39282 (NFC)

While the actually incorrect transform happens in LoopUnroll, it
is based on noalias metadata inserted by the inliner, and
ultimately manifests in GVN. Add a phase ordering test that checks
this even if our representation of noalias metadata changes in
the future.

llvm/test/Transforms/PhaseOrdering/pr39282.ll

@@ -0,0 +1,45 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -O2 -S < %s | FileCheck %s
+; RUN: opt -passes='default<O2>' -aa-pipeline=default -S < %s | FileCheck %s
+
+define void @copy(i32* noalias %to, i32* noalias %from) {
+; CHECK-LABEL: @copy(
+; CHECK-NEXT:    [[X:%.*]] = load i32, i32* [[FROM:%.*]], align 4
+; CHECK-NEXT:    store i32 [[X]], i32* [[TO:%.*]], align 4
+; CHECK-NEXT:    ret void
+;
+  %x = load i32, i32* %from
+  store i32 %x, i32* %to
+  ret void
+}
+
+; Consider that %addr1 = %addr2 + 1, in which case %addr2i and %addr1i are
+; noalias within one iteration, but may alias across iterations.
+; TODO: This is a micompile.
+define void @pr39282(i32* %addr1, i32* %addr2) {
+; CHECK-LABEL: @pr39282(
+; CHECK-NEXT:  start:
+; CHECK-NEXT:    [[X_I:%.*]] = load i32, i32* [[ADDR1:%.*]], align 4, !alias.scope !0, !noalias !3
+; CHECK-NEXT:    [[ADDR1I_1:%.*]] = getelementptr inbounds i32, i32* [[ADDR1]], i64 1
+; CHECK-NEXT:    [[ADDR2I_1:%.*]] = getelementptr inbounds i32, i32* [[ADDR2:%.*]], i64 1
+; CHECK-NEXT:    [[X_I_1:%.*]] = load i32, i32* [[ADDR1I_1]], align 4, !alias.scope !0, !noalias !3
+; CHECK-NEXT:    store i32 [[X_I]], i32* [[ADDR2]], align 4, !alias.scope !3, !noalias !0
+; CHECK-NEXT:    store i32 [[X_I_1]], i32* [[ADDR2I_1]], align 4, !alias.scope !3, !noalias !0
+; CHECK-NEXT:    ret void
+;
+start:
+  br label %body
+
+body:
+  %i = phi i32 [ 0, %start ], [ %i.next, %body ]
+  %j = and i32 %i, 1
+  %addr1i = getelementptr inbounds i32, i32* %addr1, i32 %j
+  %addr2i = getelementptr inbounds i32, i32* %addr2, i32 %j
+  call void @copy(i32* %addr2i, i32* %addr1i)
+  %i.next = add i32 %i, 1
+  %cmp = icmp slt i32 %i.next, 4
+  br i1 %cmp, label %body, label %end
+
+end:
+  ret void
+}