l0: mov r1 l0		// check that ri equals the current block
 	sub r2 r1 ri
 	recovernz r2
 	...
 	intendz r3' ri r4' 	// if r3'=0, intend to go to r4', store intention in ri
 	brz r3 r4 {ri}		// if r3 = 0, go to r4, modify type of ri in fallthrough
 	...
 	mov r1 l0		// check fallthrough was what we intended
 	sub r2 r1 ri
 	recovernz r2
 	...
 	intend r1'		// intend to jump to r1'
 	jmp r1			// jmp to r1