    -- | One ounce of sanity checking is worth 10000000000000000 ounces
    --	of staring blindly at assembly code trying to find the problem..
    --
    module SPARC.CodeGen.Sanity (
    	checkBlock
    )

    where

    import SPARC.Instr
    import SPARC.Ppr	()
    import Instruction

    import Cmm

    import Outputable

    -- | Enforce intra-block invariants.
    --
    checkBlock
    	:: CmmBasicBlock
    	-> NatBasicBlock Instr -> NatBasicBlock Instr

    checkBlock cmm block@(BasicBlock _ instrs)
    	| checkBlockInstrs instrs
    	= block

    	| otherwise
    	= pprPanic
    		("SPARC.CodeGen: bad block\n")
    		( vcat	[ text " -- cmm -----------------\n"
    			, ppr cmm
    			, text " -- native code ---------\n"
    			, ppr block ])

    checkBlockInstrs :: [Instr] -> Bool
    checkBlockInstrs ii

    	-- An unconditional jumps end the block.
    	--	There must be an unconditional jump in the block, otherwise
    	--	the register liveness determinator will get the liveness
    	--	information wrong.
    	--
    	--	If the block ends with a cmm call that never returns
    	--	then there can be unreachable instructions after the jump,
    	--	but we don't mind here.
    	--
    	| instr : NOP : _	<- ii
    	, isUnconditionalJump instr
    	= True

    	-- All jumps must have a NOP in their branch delay slot.
    	--	The liveness determinator and register allocators aren't smart
    	--	enough to handle branch delay slots.
    	--
    	| instr : NOP : is	<- ii
    	, isJumpishInstr instr
    	= checkBlockInstrs is

    	-- keep checking
    	| _:i2:is		<- ii
    	= checkBlockInstrs (i2:is)

    	-- this block is no good
    	| otherwise
    	= False