    -- | 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 :: CmmBlock
               -> 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