possible bug in `initializes` semantics

[regehr]

here's a function:

define void @f(ptr %0, ptr %1) {
  %3 = load i64, ptr %1, align 4
  store i64 %3, ptr %0, align 4
  ret void
}

opt infers that %0 initializes 8 bytes of storage. this is fine by my reading of langref (the fact that %1 might alias some or all of the initialized storage is OK, according to the text)

but Alive is not happy about the aliasing case:

~$ ~/alive2-regehr/build/alive-tv foo.ll

----------------------------------------
define void @f(ptr %#0, ptr %#1) {
#2:
  %#3 = load i64, ptr %#1, align 4
  store i64 %#3, ptr %#0, align 4
  ret void
}
=>
define void @f(ptr nocapture noread initializes((0, 8)) %#0, ptr nocapture nowrite %#1) nofree willreturn memory(argmem: readwrite) {
#2:
  %#3 = load i64, ptr nocapture nowrite %#1, align 4
  store i64 %#3, ptr nocapture noread initializes((0, 8)) %#0, align 4
  ret void
}
Transformation doesn't verify!

ERROR: Source is more defined than target

Example:
ptr %#0 = pointer(non-local, block_id=1, offset=0, attrs=8) / Address=#x04
ptr %#1 = pointer(non-local, block_id=1, offset=0, attrs=8) / Address=#x04

Source:
i64 %#3 = poison

SOURCE MEMORY STATE
===================
NON-LOCAL BLOCKS:
Block 0 >	size: 0	align: 4	alloc type: 0	alive: false	address: 0
Block 1 >	size: 9	align: 1	alloc type: 0	alive: true	address: 4
Block 2 >	size: 0	align: 1	alloc type: 0	alive: true	address: 4

Target:
i64 %#3 = UB triggered!


Summary:
  0 correct transformations
  1 incorrect transformations
  0 failed-to-prove transformations
  0 Alive2 errors
~$ 

[regehr]

just a note that this one comes up a lot for me in practice -- I'll start stripping initializes out of lifted code for the time being