False positive when devirtualizing call with memory attributes

[nikic]

https://alive2.llvm.org/ce/z/cyCxQ6

@vtable = constant ptr @fn
declare void @fn() memory(none)

define void @src() {
  %fn = load ptr, ptr @vtable
  call void %fn()
  ret void
}

Results in:

ERROR: Source is more defined than target

Example:

Source:
  >> Jump to %#0
ptr %fn = pointer(non-local, block_id=2, offset=0)
void = function did not return!

SOURCE MEMORY STATE
===================
NON-LOCAL BLOCKS:
Block 0 >	size: 0	align: 8	alloc type: 0	alive: false	address: 0
Block 1 >	size: 8	align: 8	alloc type: 0	alive: true	address: 128	const
Block 2 >	size: 8	align: 8	alloc type: 0	alive: true	address: 8	const
Block 3 >	size: 4	align: 4	alloc type: 0	alive: true	address: 4
Block 4 >	size: 1	align: 8	alloc type: 0	alive: true	address: 128

Target:
  >> Jump to %#0
Function @fn triggered UB

Seen in https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=a4dd1863f139db90&test=Transforms%2FSimpleLoopUnswitch%2Fmemssa-readnone-access.ll.