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|
-- | The assignment of virtual registers to stack slots
-- We have lots of stack slots. Memory-to-memory moves are a pain on most
-- architectures. Therefore, we avoid having to generate memory-to-memory moves
-- by simply giving every virtual register its own stack slot.
-- The StackMap stack map keeps track of virtual register - stack slot
-- associations and of which stack slots are still free. Once it has been
-- associated, a stack slot is never "freed" or removed from the StackMap again,
-- it remains associated until we are done with the current CmmProc.
--
module GHC.CmmToAsm.Reg.Linear.StackMap (
StackSlot,
StackMap(..),
emptyStackMap,
getStackSlotFor,
getStackUse
)
where
import GhcPrelude
import UniqFM
import Unique
-- | Identifier for a stack slot.
type StackSlot = Int
data StackMap
= StackMap
{ -- | The slots that are still available to be allocated.
stackMapNextFreeSlot :: !Int
-- | Assignment of vregs to stack slots.
, stackMapAssignment :: UniqFM StackSlot }
-- | An empty stack map, with all slots available.
emptyStackMap :: StackMap
emptyStackMap = StackMap 0 emptyUFM
-- | If this vreg unique already has a stack assignment then return the slot number,
-- otherwise allocate a new slot, and update the map.
--
getStackSlotFor :: StackMap -> Unique -> (StackMap, Int)
getStackSlotFor fs@(StackMap _ reserved) reg
| Just slot <- lookupUFM reserved reg = (fs, slot)
getStackSlotFor (StackMap freeSlot reserved) reg =
(StackMap (freeSlot+1) (addToUFM reserved reg freeSlot), freeSlot)
-- | Return the number of stack slots that were allocated
getStackUse :: StackMap -> Int
getStackUse (StackMap freeSlot _) = freeSlot
|
