Test: Transforms/InstSimplify/insertelement.ll
Summary: We can't remove insertelement undef to a vector, since it may be replacing a poison value.

define <4 x i32> @PR1286(<4 x i32> %A) {
  %B = insertelement <4 x i32> %A, i32 undef, i32 1
  ret <4 x i32> %B
}
=>
define <4 x i32> @PR1286(<4 x i32> %A) {
  ret <4 x i32> %A
}
Transformation doesn't verify!
ERROR: Target is more poisonous than source

Example:
<4 x i32> %A = < poison, poison, poison, poison >

Source:
<4 x i32> %B = < poison, undef, poison, poison >

Target:
Source value: < poison, undef, poison, poison >
Target value: < poison, poison, poison, poison >


Report: https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=ed3ac07d4817b221&test=Transforms%2FInstSimplify%2Finsertelement.ll