test compile
target x86_64 machinst

function %f0(b8) -> b64 {
block0(v0: b8):
  v1 = bextend.b64 v0
  return v1
}

; check:  pushq   %rbp
; nextln: movq    %rsp, %rbp
; nextln: movsbq  %dil, %rsi
; nextln: movq    %rsi, %rax
; nextln: movq    %rbp, %rsp
; nextln: popq    %rbp
; nextln: ret