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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 RegAlloc.Linear.StackMap (
StackSlot,
StackMap(..),
emptyStackMap,
getStackSlotFor
)
where
import RegAlloc.Linear.FreeRegs
import Outputable
import Platform
import UniqFM
import Unique
-- | Identifier for a stack slot.
type StackSlot = Int
data StackMap
= StackMap
{ -- | The slots that are still available to be allocated.
stackMapFreeSlots :: [StackSlot]
-- | Assignment of vregs to stack slots.
, stackMapAssignment :: UniqFM StackSlot }
-- | An empty stack map, with all slots available.
emptyStackMap :: Platform -> StackMap
emptyStackMap platform = StackMap [0 .. maxSpillSlots platform] 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 (StackMap [] _) _
-- This happens all the time when trying to compile darcs' SHA1.hs, see Track #1993
-- SHA1.lhs has also been added to the Crypto library on Hackage,
-- so we see this all the time.
--
-- It would be better to automatically invoke the graph allocator, or do something
-- else besides panicing, but that's a job for a different day. -- BL 2009/02
--
= panic $ "RegAllocLinear.getStackSlotFor: out of stack slots\n"
++ " If you are trying to compile SHA1.hs from the crypto library then this\n"
++ " is a known limitation in the linear allocator.\n"
++ "\n"
++ " Try enabling the graph colouring allocator with -fregs-graph instead."
++ " You can still file a bug report if you like.\n"
getStackSlotFor fs@(StackMap (freeSlot:stack') reserved) reg =
case lookupUFM reserved reg of
Just slot -> (fs, slot)
Nothing -> (StackMap stack' (addToUFM reserved reg freeSlot), freeSlot)
|