ldexp intrinsic not understood

[arsenm]

https://alive2.llvm.org/ce/z/6Rw7uw

----------------------------------------
declare float @llvm.ldexp.f32.i32(float, i32) nofree willreturn memory(none)

define float @src(float %x, i32 %y) {
#0:
  %z = call float @llvm.ldexp.f32.i32(float %x, i32 %y) nofree willreturn memory(none)
  ret float %z
}
=>
declare float @llvm.ldexp.f32.i32(float, i32) nofree willreturn memory(none)

define float @tgt(float %x, i32 %y) {
#0:
  %z = call float @llvm.ldexp.f32.i32(float %x, i32 0) nofree willreturn memory(none)
  ret float %z
}
ERROR: Couldn't prove the correctness of the transformation
Alive2 approximated the semantics of the programs and therefore we
cannot conclude whether the bug found is valid or not.

Approximations done:
 - Unknown libcall: @llvm.ldexp.f32.i32

[regehr]

@MitchBriles want to take a crack at adding this intrinsic?

[MitchBriles]

Yeah, I'll give it a go!