never executed always true always false

    1 -- | One ounce of sanity checking is worth 10000000000000000 ounces
    2 -- of staring blindly at assembly code trying to find the problem..
    3 module GHC.CmmToAsm.SPARC.CodeGen.Sanity (
    4         checkBlock
    5 )
    6 
    7 where
    8 
    9 import GHC.Prelude
   10 import GHC.Platform
   11 
   12 import GHC.CmmToAsm.SPARC.Instr
   13 import GHC.CmmToAsm.SPARC.Ppr        () -- For Outputable instances
   14 import GHC.CmmToAsm.Types
   15 
   16 import GHC.Cmm
   17 
   18 import GHC.Utils.Outputable
   19 import GHC.Utils.Panic
   20 
   21 
   22 -- | Enforce intra-block invariants.
   23 --
   24 checkBlock :: Platform
   25            -> CmmBlock
   26            -> NatBasicBlock Instr
   27            -> NatBasicBlock Instr
   28 
   29 checkBlock platform cmm block@(BasicBlock _ instrs)
   30         | checkBlockInstrs instrs
   31         = block
   32 
   33         | otherwise
   34         = pprPanic
   35                 ("SPARC.CodeGen: bad block\n")
   36                 ( vcat  [ text " -- cmm -----------------\n"
   37                         , pdoc platform cmm
   38                         , text " -- native code ---------\n"
   39                         , pdoc platform block ])
   40 
   41 
   42 checkBlockInstrs :: [Instr] -> Bool
   43 checkBlockInstrs ii
   44 
   45         -- An unconditional jumps end the block.
   46         --      There must be an unconditional jump in the block, otherwise
   47         --      the register liveness determinator will get the liveness
   48         --      information wrong.
   49         --
   50         --      If the block ends with a cmm call that never returns
   51         --      then there can be unreachable instructions after the jump,
   52         --      but we don't mind here.
   53         --
   54         | instr : NOP : _       <- ii
   55         , isUnconditionalJump instr
   56         = True
   57 
   58         -- All jumps must have a NOP in their branch delay slot.
   59         --      The liveness determinator and register allocators aren't smart
   60         --      enough to handle branch delay slots.
   61         --
   62         | instr : NOP : is      <- ii
   63         , isJumpishInstr instr
   64         = checkBlockInstrs is
   65 
   66         -- keep checking
   67         | _:i2:is               <- ii
   68         = checkBlockInstrs (i2:is)
   69 
   70         -- this block is no good
   71         | otherwise
   72         = False