path: root/compiler/GHC/Cmm.hs

-- Cmm representations using Hoopl's Graph CmmNode e x.
{-# LANGUAGE GADTs #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE ExplicitNamespaces #-}

module GHC.Cmm (
     -- * Cmm top-level datatypes
     CmmProgram, CmmGroup, CmmGroupSRTs, RawCmmGroup, GenCmmGroup,
     CmmDecl, CmmDeclSRTs, GenCmmDecl(..),
     CmmGraph, GenCmmGraph(..),
     CmmBlock, RawCmmDecl,
     Section(..), SectionType(..),
     GenCmmStatics(..), type CmmStatics, type RawCmmStatics, CmmStatic(..),
     SectionProtection(..), sectionProtection,

     -- ** Blocks containing lists
     GenBasicBlock(..), blockId,
     ListGraph(..), pprBBlock,

     -- * Info Tables
     CmmTopInfo(..), CmmStackInfo(..), CmmInfoTable(..), topInfoTable,
     ClosureTypeInfo(..),
     ProfilingInfo(..), ConstrDescription,

     -- * Statements, expressions and types
     module GHC.Cmm.Node,
     module GHC.Cmm.Expr,
  ) where

import GHC.Prelude

import GHC.Types.Id
import GHC.Types.CostCentre
import GHC.Cmm.CLabel
import GHC.Cmm.BlockId
import GHC.Cmm.Node
import GHC.Runtime.Heap.Layout
import GHC.Cmm.Expr
import GHC.Cmm.Dataflow.Block
import GHC.Cmm.Dataflow.Collections
import GHC.Cmm.Dataflow.Graph
import GHC.Cmm.Dataflow.Label
import GHC.Utils.Outputable
import Data.ByteString (ByteString)

-----------------------------------------------------------------------------
--  Cmm, GenCmm
-----------------------------------------------------------------------------

-- A CmmProgram is a list of CmmGroups
-- A CmmGroup is a list of top-level declarations

-- When object-splitting is on, each group is compiled into a separate
-- .o file. So typically we put closely related stuff in a CmmGroup.
-- Section-splitting follows suit and makes one .text subsection for each
-- CmmGroup.

type CmmProgram = [CmmGroup]

type GenCmmGroup d h g = [GenCmmDecl d h g]
-- | Cmm group before SRT generation
type CmmGroup     = GenCmmGroup CmmStatics    CmmTopInfo               CmmGraph
-- | Cmm group with SRTs
type CmmGroupSRTs = GenCmmGroup RawCmmStatics CmmTopInfo               CmmGraph
-- | "Raw" cmm group (TODO (osa): not sure what that means)
type RawCmmGroup  = GenCmmGroup RawCmmStatics (LabelMap RawCmmStatics) CmmGraph

-----------------------------------------------------------------------------
--  CmmDecl, GenCmmDecl
-----------------------------------------------------------------------------

-- GenCmmDecl is abstracted over
--   d, the type of static data elements in CmmData
--   h, the static info preceding the code of a CmmProc
--   g, the control-flow graph of a CmmProc
--
-- We expect there to be two main instances of this type:
--   (a) C--, i.e. populated with various C-- constructs
--   (b) Native code, populated with data/instructions

-- | A top-level chunk, abstracted over the type of the contents of
-- the basic blocks (Cmm or instructions are the likely instantiations).
data GenCmmDecl d h g
  = CmmProc     -- A procedure
     h                 -- Extra header such as the info table
     CLabel            -- Entry label
     [GlobalReg]       -- Registers live on entry. Note that the set of live
                       -- registers will be correct in generated C-- code, but
                       -- not in hand-written C-- code. However,
                       -- splitAtProcPoints calculates correct liveness
                       -- information for CmmProcs.
     g                 -- Control-flow graph for the procedure's code

  | CmmData     -- Static data
        Section
        d

type CmmDecl     = GenCmmDecl CmmStatics    CmmTopInfo CmmGraph
type CmmDeclSRTs = GenCmmDecl RawCmmStatics CmmTopInfo CmmGraph

type RawCmmDecl
   = GenCmmDecl
        RawCmmStatics
        (LabelMap RawCmmStatics)
        CmmGraph

-----------------------------------------------------------------------------
--     Graphs
-----------------------------------------------------------------------------

type CmmGraph = GenCmmGraph CmmNode
data GenCmmGraph n = CmmGraph { g_entry :: BlockId, g_graph :: Graph n C C }
type CmmBlock = Block CmmNode C C

-----------------------------------------------------------------------------
--     Info Tables
-----------------------------------------------------------------------------

-- | CmmTopInfo is attached to each CmmDecl (see defn of CmmGroup), and contains
-- the extra info (beyond the executable code) that belongs to that CmmDecl.
data CmmTopInfo   = TopInfo { info_tbls  :: LabelMap CmmInfoTable
                            , stack_info :: CmmStackInfo }

topInfoTable :: GenCmmDecl a CmmTopInfo (GenCmmGraph n) -> Maybe CmmInfoTable
topInfoTable (CmmProc infos _ _ g) = mapLookup (g_entry g) (info_tbls infos)
topInfoTable _                     = Nothing

data CmmStackInfo
   = StackInfo {
       arg_space :: ByteOff,
               -- number of bytes of arguments on the stack on entry to the
               -- the proc.  This is filled in by GHC.StgToCmm.codeGen, and
               -- used by the stack allocator later.
       do_layout :: Bool
               -- Do automatic stack layout for this proc.  This is
               -- True for all code generated by the code generator,
               -- but is occasionally False for hand-written Cmm where
               -- we want to do the stack manipulation manually.
  }

-- | Info table as a haskell data type
data CmmInfoTable
  = CmmInfoTable {
      cit_lbl  :: CLabel, -- Info table label
      cit_rep  :: SMRep,
      cit_prof :: ProfilingInfo,
      cit_srt  :: Maybe CLabel,   -- empty, or a closure address
      cit_clo  :: Maybe (Id, CostCentreStack)
        -- Just (id,ccs) <=> build a static closure later
        -- Nothing <=> don't build a static closure
        --
        -- Static closures for FUNs and THUNKs are *not* generated by
        -- the code generator, because we might want to add SRT
        -- entries to them later (for FUNs at least; THUNKs are
        -- treated the same for consistency). See Note [SRTs] in
        -- GHC.Cmm.Info.Build, in particular the [FUN] optimisation.
        --
        -- This is strictly speaking not a part of the info table that
        -- will be finally generated, but it's the only convenient
        -- place to convey this information from the code generator to
        -- where we build the static closures in
        -- GHC.Cmm.Info.Build.doSRTs.
    }

data ProfilingInfo
  = NoProfilingInfo
  | ProfilingInfo ByteString ByteString -- closure_type, closure_desc

-----------------------------------------------------------------------------
--              Static Data
-----------------------------------------------------------------------------

data SectionType
  = Text
  | Data
  | ReadOnlyData
  | RelocatableReadOnlyData
  | UninitialisedData
  | ReadOnlyData16      -- .rodata.cst16 on x86_64, 16-byte aligned
  | CString
  | OtherSection String
  deriving (Show)

data SectionProtection
  = ReadWriteSection
  | ReadOnlySection
  | WriteProtectedSection -- See Note [Relocatable Read-Only Data]
  deriving (Eq)

-- | Should a data in this section be considered constant at runtime
sectionProtection :: Section -> SectionProtection
sectionProtection (Section t _) = case t of
    Text                    -> ReadOnlySection
    ReadOnlyData            -> ReadOnlySection
    RelocatableReadOnlyData -> WriteProtectedSection
    ReadOnlyData16          -> ReadOnlySection
    CString                 -> ReadOnlySection
    Data                    -> ReadWriteSection
    UninitialisedData       -> ReadWriteSection
    (OtherSection _)        -> ReadWriteSection

{-
Note [Relocatable Read-Only Data]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Relocatable data are only read-only after relocation at the start of the
program. They should be writable from the source code until then. Failure to
do so would end up in segfaults at execution when using linkers that do not
enforce writability of those sections, such as the gold linker.
-}

data Section = Section SectionType CLabel

data CmmStatic
  = CmmStaticLit CmmLit
        -- ^ a literal value, size given by cmmLitRep of the literal.
  | CmmUninitialised Int
        -- ^ uninitialised data, N bytes long
  | CmmString ByteString
        -- ^ string of 8-bit values only, not zero terminated.
  | CmmFileEmbed FilePath
        -- ^ an embedded binary file

-- Static data before SRT generation
data GenCmmStatics (rawOnly :: Bool) where
    CmmStatics
      :: CLabel       -- Label of statics
      -> CmmInfoTable
      -> CostCentreStack
      -> [CmmLit]     -- Payload
      -> GenCmmStatics 'False

    -- | Static data, after SRTs are generated
    CmmStaticsRaw
      :: CLabel       -- Label of statics
      -> [CmmStatic]  -- The static data itself
      -> GenCmmStatics a

type CmmStatics    = GenCmmStatics 'False
type RawCmmStatics = GenCmmStatics 'True

-- -----------------------------------------------------------------------------
-- Basic blocks consisting of lists

-- These are used by the LLVM and NCG backends, when populating Cmm
-- with lists of instructions.

data GenBasicBlock i = BasicBlock BlockId [i]

-- | The branch block id is that of the first block in
-- the branch, which is that branch's entry point
blockId :: GenBasicBlock i -> BlockId
blockId (BasicBlock blk_id _ ) = blk_id

newtype ListGraph i = ListGraph [GenBasicBlock i]

instance Outputable instr => Outputable (ListGraph instr) where
    ppr (ListGraph blocks) = vcat (map ppr blocks)

instance Outputable instr => Outputable (GenBasicBlock instr) where
    ppr = pprBBlock

pprBBlock :: Outputable stmt => GenBasicBlock stmt -> SDoc
pprBBlock (BasicBlock ident stmts) =
    hang (ppr ident <> colon) 4 (vcat (map ppr stmts))