[LV] Add test case for #119173. NFC

This showcases a miscompile involving a widened reduction-phi.

Author: lukel97

llvm/test/Transforms/LoopVectorize/AArch64/mul-simplification.ll

@@ -56,9 +56,59 @@ exit:
   %res = phi i64 [ %red.next, %loop ]
   ret i64 %res
 }
+
+define i32 @add_reduction_select_operand_constant_but_non_uniform() {
+; CHECK-LABEL: define i32 @add_reduction_select_operand_constant_but_non_uniform() {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
+; CHECK:       [[VECTOR_PH]]:
+; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
+; CHECK:       [[VECTOR_BODY]]:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x i32> [ <i32 42, i32 0, i32 0, i32 0>, %[[VECTOR_PH]] ], [ splat (i32 42), %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <4 x i32> [ zeroinitializer, %[[VECTOR_PH]] ], [ splat (i32 42), %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 8
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp eq i32 [[INDEX_NEXT]], 64
+; CHECK-NEXT:    br i1 [[TMP0]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
+; CHECK:       [[MIDDLE_BLOCK]]:
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> splat (i32 84))
+; CHECK-NEXT:    br i1 true, label %[[EXIT:.*]], label %[[SCALAR_PH]]
+; CHECK:       [[SCALAR_PH]]:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ 64, %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP1]], %[[MIDDLE_BLOCK]] ], [ 42, %[[ENTRY]] ]
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[ADD2_REASS:%.*]], %[[LOOP]] ]
+; CHECK-NEXT:    [[RDX:%.*]] = phi i32 [ [[BC_MERGE_RDX]], %[[SCALAR_PH]] ], [ [[RDX_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT:    [[ADD2_REASS]] = add i32 [[IV]], 1
+; CHECK-NEXT:    [[RDX_NEXT]] = add i32 0, [[RDX]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[ADD2_REASS]], 64
+; CHECK-NEXT:    br i1 [[CMP]], label %[[LOOP]], label %[[EXIT]], !llvm.loop [[LOOP5:![0-9]+]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    [[ADD_LCSSA:%.*]] = phi i32 [ [[RDX_NEXT]], %[[LOOP]] ], [ [[TMP1]], %[[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    ret i32 [[ADD_LCSSA]]
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+  %rdx = phi i32 [ 42, %entry ], [ %rdx.next, %loop ]
+
+  %iv.next = add i32 %iv, 1
+  %rdx.next = add i32 0, %rdx
+
+  %cmp = icmp ult i32 %iv.next, 64
+  br i1 %cmp, label %loop, label %exit
+
+exit:
+  ret i32 %rdx.next
+}
 ;.
 ; CHECK: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]], [[META2:![0-9]+]]}
 ; CHECK: [[META1]] = !{!"llvm.loop.isvectorized", i32 1}
 ; CHECK: [[META2]] = !{!"llvm.loop.unroll.runtime.disable"}
 ; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META2]], [[META1]]}
+; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META1]], [[META2]]}
+; CHECK: [[LOOP5]] = distinct !{[[LOOP5]], [[META2]], [[META1]]}
 ;.