AllocationSizeMovingUp.hs

-- | Move size variables used in allocation statements upwards in the bodies of
-- a program to enable more memory block reuses.
--
-- This should be run *before* the reuse pass, as it enables more optimisations.
-- Specifically, it helps with reusing memory whose size needs to be changed to
-- be the maximum of itself and another size -- and so, that other size needs to
-- have been hoisted so that is in scope at that point.  This module hoists all
-- sizes as much as possible.
module Futhark.Optimise.MemoryBlockMerging.Reuse.AllocationSizeMovingUp
  ( moveUpAllocSizesFunDef
  ) where

import qualified Data.Map.Strict as M
import Data.Maybe (fromMaybe)

import Futhark.Representation.AST
import Futhark.Representation.ExplicitMemory (ExplicitMemory)

import Futhark.Optimise.MemoryBlockMerging.CrudeMovingUp
import Futhark.Optimise.MemoryBlockMerging.Reuse.AllocationSizes

findAllocSizeHoistees :: Body ExplicitMemory -> Maybe [FParam ExplicitMemory]
                      -> [VName]
findAllocSizeHoistees body params =
  let subexps = map fst $ M.elems
                $ memBlockSizesParamsBodyNonRec (fromMaybe [] params) body
  in subExpVars subexps

moveUpAllocSizesFunDef :: FunDef ExplicitMemory
                      -> FunDef ExplicitMemory
moveUpAllocSizesFunDef fundef =
  moveUpInFunDef fundef findAllocSizeHoistees