Add test for PR47322 (NFC)

Author: nikic

llvm/test/Transforms/InstCombine/select.ll

@@ -2487,3 +2487,19 @@ define <2 x i32> @true_undef_vec(i1 %cond, <2 x i32> %x) {
   %s = select i1 %cond, <2 x i32> undef, <2 x i32> %x
   ret <2 x i32> %s
 }
+
+; FIXME: This is a miscompile!
+define i32 @pr47322_more_poisonous_replacement(i32 %arg) {
+; CHECK-LABEL: @pr47322_more_poisonous_replacement(
+; CHECK-NEXT:    [[TRAILING:%.*]] = call i32 @llvm.cttz.i32(i32 [[ARG:%.*]], i1 immarg true), [[RNG0:!range !.*]]
+; CHECK-NEXT:    [[SHIFTED:%.*]] = lshr i32 [[ARG]], [[TRAILING]]
+; CHECK-NEXT:    ret i32 [[SHIFTED]]
+;
+  %cmp = icmp eq i32 %arg, 0
+  %trailing = call i32 @llvm.cttz.i32(i32 %arg, i1 immarg true)
+  %shifted = lshr i32 %arg, %trailing
+  %r1.sroa.0.1 = select i1 %cmp, i32 0, i32 %shifted
+  ret i32 %r1.sroa.0.1
+}
+
+declare i32 @llvm.cttz.i32(i32, i1 immarg)