Compiler emits unreachable assembly code

[vbgl]

The following jasmin program

export fn main(reg u32 x) -> reg u32 {
  reg u32 s = 0;
  if x >s s {
    while (x > 1) { x >>= 1; }
  } else { s -= 1; }
  return s;
}

is compiled to

main:
	movl	$0, %eax
	cmpl	%eax, %edi
	jnle	Lmain$3
	addl	$-1, %eax
	jmp 	Lmain$2
Lmain$1:
	jmp 	Lmain$3
Lmain$4:
	shrl	$1, %edi
Lmain$3:
	cmpl	$1, %edi
	jnbe	Lmain$4
Lmain$2:
	ret

Label Lmain$1 is unreacheable so the instruction jmp Lmain$3 is dead.

[eponier]

It seems that tunneling does only half of its job?