GHC/Cmm/Info/Build.hs

    {-# LANGUAGE GADTs, BangPatterns, RecordWildCards,
        GeneralizedNewtypeDeriving, NondecreasingIndentation, TupleSections,
        ScopedTypeVariables, OverloadedStrings, LambdaCase #-}
    {-# LANGUAGE MultiParamTypeClasses #-}
    {-# LANGUAGE FlexibleInstances #-}
    {-# LANGUAGE StandaloneDeriving #-}
    {-# LANGUAGE DerivingStrategies #-}
    {-# LANGUAGE FlexibleContexts #-}
    {-# LANGUAGE UndecidableInstances #-}

    module GHC.Cmm.Info.Build
      ( CAFSet, CAFEnv, cafAnal, cafAnalData
      , doSRTs, ModuleSRTInfo (..), emptySRT
      , SRTMap, srtMapNonCAFs
      ) where

    import GHC.Prelude hiding (succ)

    import GHC.Platform
    import GHC.Platform.Profile

    import GHC.Types.Id
    import GHC.Types.Id.Info
    import GHC.Cmm.BlockId
    import GHC.Cmm.Dataflow.Block
    import GHC.Cmm.Dataflow.Graph
    import GHC.Cmm.Dataflow.Label
    import GHC.Cmm.Dataflow.Collections
    import GHC.Cmm.Dataflow
    import GHC.Unit.Module
    import GHC.Data.Graph.Directed
    import GHC.Cmm.CLabel
    import GHC.Cmm
    import GHC.Cmm.Utils
    import GHC.Driver.Session
    import GHC.Data.Maybe
    import GHC.Utils.Outputable
    import GHC.Utils.Panic
    import GHC.Runtime.Heap.Layout
    import GHC.Types.Unique.Supply
    import GHC.Types.CostCentre
    import GHC.StgToCmm.Heap
    import GHC.CmmToAsm

    import Control.Monad
    import Data.Map.Strict (Map)
    import qualified Data.Map.Strict as Map
    import Data.Set (Set)
    import qualified Data.Set as Set
    import Control.Monad.Trans.State
    import Control.Monad.Trans.Class
    import Data.List (unzip4)

    import GHC.Types.Name.Set

    {- Note [SRTs]

    SRTs are the mechanism by which the garbage collector can determine
    the live CAFs in the program.

    Representation
    ^^^^^^^^^^^^^^

    +------+
    | info |
    |      |     +-----+---+---+---+
    |   -------->|SRT_2| | | | | 0 |
    |------|     +-----+-|-+-|-+---+
    |      |             |   |
    | code |             |   |
    |      |             v   v

    An SRT is simply an object in the program's data segment. It has the
    same representation as a static constructor.  There are 16
    pre-compiled SRT info tables: stg_SRT_1_info, .. stg_SRT_16_info,
    representing SRT objects with 1-16 pointers, respectively.

    The entries of an SRT object point to static closures, which are either
    - FUN_STATIC, THUNK_STATIC or CONSTR
    - Another SRT (actually just a CONSTR)

    The final field of the SRT is the static link field, used by the
    garbage collector to chain together static closures that it visits and
    to determine whether a static closure has been visited or not. (see
    Note [STATIC_LINK fields])

    By traversing the transitive closure of an SRT, the GC will reach all
    of the CAFs that are reachable from the code associated with this SRT.

    If we need to create an SRT with more than 16 entries, we build a
    chain of SRT objects with all but the last having 16 entries.

    +-----+---+- -+---+---+
    |SRT16| | |   | | | 0 |
    +-----+-|-+- -+-|-+---+
            |       |
            v       v
                  +----+---+---+---+
                  |SRT2| | | | | 0 |
                  +----+-|-+-|-+---+
                         |   |
                         |   |
                         v   v

    Referring to an SRT from the info table
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    The following things have SRTs:

    - Static functions (FUN)
    - Static thunks (THUNK), ie. CAFs
    - Continuations (RET_SMALL, etc.)

    In each case, the info table points to the SRT.

    - info->srt is zero if there's no SRT, otherwise:
    - info->srt == 1 and info->f.srt_offset points to the SRT

    e.g. for a FUN with an SRT:

    StgFunInfoTable       +------+
      info->f.srt_offset  |  ------------> offset to SRT object
    StgStdInfoTable       +------+
      info->layout.ptrs   | ...  |
      info->layout.nptrs  | ...  |
      info->srt           |  1   |
      info->type          | ...  |
                          |------|

    On x86_64, we optimise the info table representation further.  The
    offset to the SRT can be stored in 32 bits (all code lives within a
    2GB region in x86_64's small memory model), so we can save a word in
    the info table by storing the srt_offset in the srt field, which is
    half a word.

    On x86_64 with TABLES_NEXT_TO_CODE (except on MachO, due to #15169):

    - info->srt is zero if there's no SRT, otherwise:
    - info->srt is an offset from the info pointer to the SRT object

    StgStdInfoTable       +------+
      info->layout.ptrs   |      |
      info->layout.nptrs  |      |
      info->srt           |  ------------> offset to SRT object
                          |------|

    EXAMPLE
    ^^^^^^^

    f = \x. ... g ...
      where
        g = \y. ... h ... c1 ...
        h = \z. ... c2 ...

    c1 & c2 are CAFs

    g and h are local functions, but they have no static closures.  When
    we generate code for f, we start with a CmmGroup of four CmmDecls:

       [ f_closure, f_entry, g_entry, h_entry ]

    we process each CmmDecl separately in cpsTop, giving us a list of
    CmmDecls. e.g. for f_entry, we might end up with

       [ f_entry, f1_ret, f2_proc ]

    where f1_ret is a return point, and f2_proc is a proc-point.  We have
    a CAFSet for each of these CmmDecls, let's suppose they are

       [ f_entry{g_info}, f1_ret{g_info}, f2_proc{} ]
       [ g_entry{h_info, c1_closure} ]
       [ h_entry{c2_closure} ]

    Next, we make an SRT for each of these functions:

      f_srt : [g_info]
      g_srt : [h_info, c1_closure]
      h_srt : [c2_closure]

    Now, for g_info and h_info, we want to refer to the SRTs for g and h
    respectively, which we'll label g_srt and h_srt:

      f_srt : [g_srt]
      g_srt : [h_srt, c1_closure]
      h_srt : [c2_closure]

    Now, when an SRT has a single entry, we don't actually generate an SRT
    closure for it, instead we just replace references to it with its
    single element.  So, since h_srt == c2_closure, we have

      f_srt : [g_srt]
      g_srt : [c2_closure, c1_closure]
      h_srt : [c2_closure]

    and the only SRT closure we generate is

      g_srt = SRT_2 [c2_closure, c1_closure]

    Algorithm
    ^^^^^^^^^

    0. let srtMap :: Map CAFLabel (Maybe SRTEntry) = {}
       Maps closures to their SRT entries (i.e. how they appear in a SRT payload)

    1. Start with decls :: [CmmDecl]. This corresponds to an SCC of bindings in STG
       after code-generation.

    2. CPS-convert each CmmDecl (cpsTop), resulting in a list [CmmDecl]. There might
       be multiple CmmDecls in the result, due to proc-point splitting.

    3. In cpsTop, *before* proc-point splitting, when we still have a single
       CmmDecl, we do cafAnal for procs:

       * cafAnal performs a backwards analysis on the code blocks

       * For each labelled block, the analysis produces a CAFSet (= Set CAFLabel),
         representing all the CAFLabels reachable from this label.

       * A label is added to the set if it refers to a FUN, THUNK, or RET,
         and its CafInfo /= NoCafRefs.
         (NB. all CafInfo for Ids in the current module should be initialised to
         MayHaveCafRefs)

       * The result is CAFEnv = LabelMap CAFSet

       (Why *before* proc-point splitting? Because the analysis needs to propagate
       information across branches, and proc-point splitting turns branches into
       CmmCalls to top-level CmmDecls.  The analysis would fail to find all the
       references to CAFFY labels if we did it after proc-point splitting.)

       For static data, cafAnalData simply returns set of all labels that refer to a
       FUN, THUNK, and RET whose CafInfos /= NoCafRefs.

    4. The result of cpsTop is (CAFEnv, [CmmDecl]) for procs and (CAFSet, CmmDecl)
       for static data. So after `mapM cpsTop decls` we have
       [Either (CAFEnv, [CmmDecl]) (CAFSet, CmmDecl)]

    5. For procs concat the decls and union the CAFEnvs to get (CAFEnv, [CmmDecl])

    6. For static data generate a Map CLabel CAFSet (maps static data to their CAFSets)

    7. Dependency-analyse the decls using CAFEnv and CAFSets, giving us SCC CAFLabel

    8. For each SCC in dependency order
       - Let lbls :: [CAFLabel] be the non-recursive labels in this SCC
       - Apply CAFEnv to each label and concat the result :: [CAFLabel]
       - For each CAFLabel in the set apply srtMap (and ignore Nothing) to get
         srt :: [SRTEntry]
       - Make a label for this SRT, call it l
       - If the SRT is not empty (i.e. the group is CAFFY) add FUN_STATICs in the
         group to the SRT (see Note [Invalid optimisation: shortcutting])
       - Add to srtMap: lbls -> if null srt then Nothing else Just l

    9. At the end, for every top-level binding x, if srtMap x == Nothing, then the
       binding is non-CAFFY, otherwise it is CAFFY.

    Optimisations
    ^^^^^^^^^^^^^

    To reduce the code size overhead and the cost of traversing SRTs in
    the GC, we want to simplify SRTs where possible. We therefore apply
    the following optimisations.  Each has a [keyword]; search for the
    keyword in the code below to see where the optimisation is
    implemented.

    1. [Inline] we never create an SRT with a single entry, instead we
       point to the single entry directly from the info table.

       i.e. instead of

        +------+
        | info |
        |      |     +-----+---+---+
        |   -------->|SRT_1| | | 0 |
        |------|     +-----+-|-+---+
        |      |             |
        | code |             |
        |      |             v
                             C

       we can point directly to the closure:

        +------+
        | info |
        |      |
        |   -------->C
        |------|
        |      |
        | code |
        |      |

       Furthermore, the SRT for any code that refers to this info table
       can point directly to C.

       The exception to this is when we're doing dynamic linking. In that
       case, if the closure is not locally defined then we can't point to
       it directly from the info table, because this is the text section
       which cannot contain runtime relocations. In this case we skip this
       optimisation and generate the singleton SRT, because SRTs are in the
       data section and *can* have relocatable references.

    2. [FUN] A static function closure can also be an SRT, we simply put
       the SRT entries as fields in the static closure.  This makes a lot
       of sense: the static references are just like the free variables of
       the FUN closure.

       i.e. instead of

       f_closure:
       +-----+---+
       |  |  | 0 |
       +- |--+---+
          |            +------+
          |            | info |     f_srt:
          |            |      |     +-----+---+---+---+
          |            |   -------->|SRT_2| | | | + 0 |
          `----------->|------|     +-----+-|-+-|-+---+
                       |      |             |   |
                       | code |             |   |
                       |      |             v   v

       We can generate:

       f_closure:
       +-----+---+---+---+
       |  |  | | | | | 0 |
       +- |--+-|-+-|-+---+
          |    |   |   +------+
          |    v   v   | info |
          |            |      |
          |            |   0  |
          `----------->|------|
                       |      |
                       | code |
                       |      |

       (note: we can't do this for THUNKs, because the thunk gets
       overwritten when it is entered, so we wouldn't be able to share
       this SRT with other info tables that want to refer to it (see
       [Common] below). FUNs are immutable so don't have this problem.)

    3. [Common] Identical SRTs can be commoned up.

    4. [Filter] If an SRT A refers to an SRT B and a closure C, and B also
       refers to C (perhaps transitively), then we can omit the reference
       to C from A.

    Note that there are many other optimisations that we could do, but
    aren't implemented. In general, we could omit any reference from an
    SRT if everything reachable from it is also reachable from the other
    fields in the SRT. Our [Filter] optimisation is a special case of
    this.

    Another opportunity we don't exploit is this:

    A = {X,Y,Z}
    B = {Y,Z}
    C = {X,B}

    Here we could use C = {A} and therefore [Inline] C = A.
    -}

    -- ---------------------------------------------------------------------
    {-
    Note [No static object resurrection]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The "static flag" mechanism (see Note [STATIC_LINK fields] in smStorage.h) that
    the GC uses to track liveness of static objects assumes that unreachable
    objects will never become reachable again (i.e. are never "resurrected").
    Breaking this assumption can result in extremely subtle GC soundness issues
    (e.g. #15544, #20959).

    Guaranteeing that this assumption is not violated requires that all CAFfy
    static objects reachable from the object's code are reachable from its SRT.  In
    the past we have gotten this wrong in a few ways:

     * shortcutting references to FUN_STATICs to instead point to the FUN_STATIC's
       SRT. This lead to #15544 and is described in more detail in Note [Invalid
       optimisation: shortcutting].

     * omitting references to static data constructor applications. This previously
       happened due to an oversight (#20959): when generating an SRT for a
       recursive group we would drop references to the CAFfy static data
       constructors.

    To see why we cannot allow object resurrection, see the examples in the
    above-mentioned Notes.

    If a static closure definitely does not transitively refer to any CAFs, then it
    *may* be advertised as not-CAFfy in the interface file and consequently *may*
    be omitted from SRTs. Regardless of whether the closure is advertised as CAFfy
    or non-CAFfy, its STATIC_LINK field *must* be set to 3, so that it never
    appears on the static closure list.
    -}

    {-
    Note [Invalid optimisation: shortcutting]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    You might think that if we have something like

    A's SRT = {B}
    B's SRT = {X}

    that we could replace the reference to B in A's SRT with X.

    A's SRT = {X}
    B's SRT = {X}

    and thereby perhaps save a little work at runtime, because we don't
    have to visit B.

    But this is NOT valid.

    Consider these cases:

    0. B can't be a constructor, because constructors don't have SRTs

    1. B is a CAF. This is the easy one. Obviously we want A's SRT to
       point to B, so that it keeps B alive.

    2. B is a function.  This is the tricky one. The reason we can't
       shortcut in this case is that we aren't allowed to resurrect static
       objects for the reason described in Note [No static object resurrection].
       We noticed this in #15544.

    The particular case that cropped up when we tried this in #15544 was:

    - A is a thunk
    - B is a static function
    - X is a CAF
    - suppose we GC when A is alive, and B is not otherwise reachable.
    - B is "collected", meaning that it doesn't make it onto the static
      objects list during this GC, but nothing bad happens yet.
    - Next, suppose we enter A, and then call B. (remember that A refers to B)
      At the entry point to B, we GC. This puts B on the stack, as part of the
      RET_FUN stack frame that gets pushed when we GC at a function entry point.
    - This GC will now reach B
    - But because B was previous "collected", it breaks the assumption
      that static objects are never resurrected. See Note [STATIC_LINK
      fields] in rts/sm/Storage.h for why this is bad.
    - In practice, the GC thinks that B has already been visited, and so
      doesn't visit X, and catastrophe ensues.

    Note [Ticky labels in SRT analysis]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Raw Cmm data (CmmStaticsRaw) can't contain pointers so they're considered
    non-CAFFY in SRT analysis and we update the SRTMap mapping them to `Nothing`
    (meaning they're not CAFFY).

    However when building with -ticky we generate ticky CLabels using the function's
    `Name`. For example, if we have a top-level function `sat_s1rQ`, in a ticky
    build we get two IdLabels using the name `sat_s1rQ`:

    - For the function itself: IdLabel sat_s1rQ ... Entry
    - For the ticky counter: IdLabel sat_s1rQ ... RednCounts

    In these cases we really want to use the function definition for the SRT
    analysis of this Name, because that's what we export for this Name -- ticky
    counters are not exported. So we ignore ticky counters in SRT analysis (which
    are never CAFFY and never exported).

    Not doing this caused #17947 where we analysed the function first mapped the
    name to CAFFY. We then saw the ticky constructor, and because it has the same
    Name as the function and is not CAFFY we overrode the CafInfo of the name as
    non-CAFFY.
    -}

    -- ---------------------------------------------------------------------
    -- Label types

    -- Labels that come from cafAnal can be:
    --   - _closure labels for static functions or CAFs
    --   - _info labels for dynamic functions, thunks, or continuations
    --   - _entry labels for functions or thunks
    --
    -- Meanwhile the labels on top-level blocks are _entry labels.
    --
    -- To put everything in the same namespace we convert all labels to
    -- closure labels using toClosureLbl.  Note that some of these
    -- labels will not actually exist; that's ok because we're going to
    -- map them to SRTEntry later, which ranges over labels that do exist.
    --
    newtype CAFLabel = CAFLabel CLabel
      deriving (Eq,Ord)

    deriving newtype instance OutputableP env CLabel => OutputableP env CAFLabel

    type CAFSet = Set CAFLabel
    type CAFEnv = LabelMap CAFSet

    -- | Records the CAFfy references of a set of static data decls.
    type DataCAFEnv = Map CLabel CAFSet

    mkCAFLabel :: Platform -> CLabel -> CAFLabel
    mkCAFLabel platform lbl = CAFLabel (toClosureLbl platform lbl)

    -- This is a label that we can put in an SRT.  It *must* be a closure label,
    -- pointing to either a FUN_STATIC, THUNK_STATIC, or CONSTR.
    newtype SRTEntry = SRTEntry CLabel
      deriving (Eq, Ord)

    deriving newtype instance OutputableP env CLabel => OutputableP env SRTEntry

    -- ---------------------------------------------------------------------
    -- CAF analysis

    addCafLabel :: Platform -> CLabel -> CAFSet -> CAFSet
    addCafLabel platform l s
      | Just _ <- hasHaskellName l
      , let caf_label = mkCAFLabel platform l
        -- For imported Ids hasCAF will have accurate CafInfo
        -- Locals are initialized as CAFFY. We turn labels with empty SRTs into
        -- non-CAFFYs in doSRTs
      , hasCAF l
      = Set.insert caf_label s
      | otherwise
      = s

    cafAnalData
      :: Platform
      -> CmmStatics
      -> CAFSet
    cafAnalData platform st = case st of
       CmmStaticsRaw _lbl _data           -> Set.empty
       CmmStatics _lbl _itbl _ccs payload ->
           foldl' analyzeStatic Set.empty payload
         where
           analyzeStatic s lit =
             case lit of
               CmmLabel c -> addCafLabel platform c s
               CmmLabelOff c _ -> addCafLabel platform c s
               CmmLabelDiffOff c1 c2 _ _ -> addCafLabel platform c1 $! addCafLabel platform c2 s
               _ -> s

    -- |
    -- For each code block:
    --   - collect the references reachable from this code block to FUN,
    --     THUNK or RET labels for which hasCAF == True
    --
    -- This gives us a `CAFEnv`: a mapping from code block to sets of labels
    --
    cafAnal
      :: Platform
      -> LabelSet   -- The blocks representing continuations, ie. those
                    -- that will get RET info tables.  These labels will
                    -- get their own SRTs, so we don't aggregate CAFs from
                    -- references to these labels, we just use the label.
      -> CLabel     -- The top label of the proc
      -> CmmGraph
      -> CAFEnv
    cafAnal platform contLbls topLbl cmmGraph =
      analyzeCmmBwd cafLattice
        (cafTransfers platform contLbls (g_entry cmmGraph) topLbl) cmmGraph mapEmpty

    cafLattice :: DataflowLattice CAFSet
    cafLattice = DataflowLattice Set.empty add
      where
        add (OldFact old) (NewFact new) =
            let !new' = old `Set.union` new
            in changedIf (Set.size new' > Set.size old) new'

    cafTransfers :: Platform -> LabelSet -> Label -> CLabel -> TransferFun CAFSet
    cafTransfers platform contLbls entry topLbl
      block@(BlockCC eNode middle xNode) fBase =
        let joined :: CAFSet
            joined = cafsInNode xNode $! live'

            result :: CAFSet
            !result = foldNodesBwdOO cafsInNode middle joined

            facts :: [Set CAFLabel]
            facts = mapMaybe successorFact (successors xNode)

            live' :: CAFSet
            live' = joinFacts cafLattice facts

            successorFact :: Label -> Maybe (Set CAFLabel)
            successorFact s
              -- If this is a loop back to the entry, we can refer to the
              -- entry label.
              | s == entry = Just (addCafLabel platform topLbl Set.empty)
              -- If this is a continuation, we want to refer to the
              -- SRT for the continuation's info table
              | s `setMember` contLbls
              = Just (Set.singleton (mkCAFLabel platform (infoTblLbl s)))
              -- Otherwise, takes the CAF references from the destination
              | otherwise
              = lookupFact s fBase

            cafsInNode :: CmmNode e x -> CAFSet -> CAFSet
            cafsInNode node set = foldExpDeep addCafExpr node set

            addCafExpr :: CmmExpr -> Set CAFLabel -> Set CAFLabel
            addCafExpr expr !set =
              case expr of
                CmmLit (CmmLabel c) ->
                  addCafLabel platform c set
                CmmLit (CmmLabelOff c _) ->
                  addCafLabel platform c set
                CmmLit (CmmLabelDiffOff c1 c2 _ _) ->
                  addCafLabel platform c1 $! addCafLabel platform c2 set
                _ ->
                  set
        in
          srtTrace "cafTransfers" (text "block:"         <+> pdoc platform block $$
                                    text "contLbls:"     <+> ppr contLbls $$
                                    text "entry:"        <+> ppr entry $$
                                    text "topLbl:"       <+> pdoc platform topLbl $$
                                    text "cafs in exit:" <+> pdoc platform joined $$
                                    text "result:"       <+> pdoc platform result) $
            mapSingleton (entryLabel eNode) result

    -- -----------------------------------------------------------------------------
    -- ModuleSRTInfo

    data ModuleSRTInfo = ModuleSRTInfo
      { thisModule :: Module
        -- ^ Current module being compiled. Required for calling labelDynamic.
      , dedupSRTs :: Map (Set SRTEntry) SRTEntry
        -- ^ previous SRTs we've emitted, so we can de-duplicate.
        -- Used to implement the [Common] optimisation.
      , flatSRTs :: Map SRTEntry (Set SRTEntry)
        -- ^ The reverse mapping, so that we can remove redundant
        -- entries. e.g.  if we have an SRT [a,b,c], and we know that b
        -- points to [c,d], we can omit c and emit [a,b].
        -- Used to implement the [Filter] optimisation.
      , moduleSRTMap :: SRTMap
      }

    instance OutputableP env CLabel => OutputableP env ModuleSRTInfo where
      pdoc env ModuleSRTInfo{..} =
        text "ModuleSRTInfo {" $$
          (nest 4 $ text "dedupSRTs ="    <+> pdoc env dedupSRTs $$
                    text "flatSRTs ="     <+> pdoc env flatSRTs $$
                    text "moduleSRTMap =" <+> pdoc env moduleSRTMap) $$ char '}'

    emptySRT :: Module -> ModuleSRTInfo
    emptySRT mod =
      ModuleSRTInfo
        { thisModule = mod
        , dedupSRTs = Map.empty
        , flatSRTs = Map.empty
        , moduleSRTMap = Map.empty
        }

    -- -----------------------------------------------------------------------------
    -- Constructing SRTs

    {- Implementation notes

    - In each CmmDecl there is a mapping info_tbls from Label -> CmmInfoTable

    - The entry in info_tbls corresponding to g_entry is the closure info
      table, the rest are continuations.

    - Each entry in info_tbls possibly needs an SRT.  We need to make a
      label for each of these.

    - We get the CAFSet for each entry from the CAFEnv

    -}

    data SomeLabel
      = BlockLabel !Label
      | DeclLabel CLabel
      deriving (Eq, Ord)

    instance OutputableP env CLabel => OutputableP env SomeLabel where
       pdoc env = \case
          BlockLabel l -> text "b:" <+> pdoc env l
          DeclLabel l  -> text "s:" <+> pdoc env l

    getBlockLabel :: SomeLabel -> Maybe Label
    getBlockLabel (BlockLabel l) = Just l
    getBlockLabel (DeclLabel _) = Nothing

    getBlockLabels :: [SomeLabel] -> [Label]
    getBlockLabels = mapMaybe getBlockLabel

    -- | Return a (Label,CLabel) pair for each labelled block of a CmmDecl,
    --   where the label is
    --   - the info label for a continuation or dynamic closure
    --   - the closure label for a top-level function (not a CAF)
    getLabelledBlocks :: Platform -> CmmDecl -> [(SomeLabel, CAFLabel)]
    getLabelledBlocks platform decl = case decl of
       CmmData _ (CmmStaticsRaw _ _)    -> []
       CmmData _ (CmmStatics lbl _ _ _) -> [ (DeclLabel lbl, mkCAFLabel platform lbl) ]
       CmmProc top_info _ _ _           -> [ (BlockLabel blockId, caf_lbl)
                                           | (blockId, info) <- mapToList (info_tbls top_info)
                                           , let rep = cit_rep info
                                           , not (isStaticRep rep) || not (isThunkRep rep)
                                           , let !caf_lbl = mkCAFLabel platform (cit_lbl info)
                                           ]

    -- | Put the labelled blocks that we will be annotating with SRTs into
    -- dependency order.  This is so that we can process them one at a
    -- time, resolving references to earlier blocks to point to their
    -- SRTs. CAFs themselves are not included here; see getCAFs below.
    depAnalSRTs
      :: Platform
      -> CAFEnv
      -> Map CLabel CAFSet -- CAFEnv for statics
      -> [CmmDecl]
      -> [SCC (SomeLabel, CAFLabel, Set CAFLabel)]
    depAnalSRTs platform cafEnv cafEnv_static decls =
      srtTrace "depAnalSRTs" (text "decls:"  <+> pdoc platform decls $$
                               text "nodes:" <+> pdoc platform (map node_payload nodes) $$
                               text "graph:" <+> pdoc platform graph) graph
     where
      labelledBlocks :: [(SomeLabel, CAFLabel)]
      labelledBlocks = concatMap (getLabelledBlocks platform) decls
      labelToBlock :: Map CAFLabel SomeLabel
      labelToBlock = foldl' (\m (v,k) -> Map.insert k v m) Map.empty labelledBlocks

      nodes :: [Node SomeLabel (SomeLabel, CAFLabel, Set CAFLabel)]
      nodes = [ DigraphNode (l,lbl,cafs') l
                  (mapMaybe (flip Map.lookup labelToBlock) (Set.toList cafs'))
              | (l, lbl) <- labelledBlocks
              , Just (cafs :: Set CAFLabel) <-
                  [case l of
                     BlockLabel l -> mapLookup l cafEnv
                     DeclLabel cl -> Map.lookup cl cafEnv_static]
              , let cafs' = Set.delete lbl cafs
              ]

      graph :: [SCC (SomeLabel, CAFLabel, Set CAFLabel)]
      graph = stronglyConnCompFromEdgedVerticesOrd nodes

    -- | Get (Label, CAFLabel, Set CAFLabel) for each block that represents a CAF.
    -- These are treated differently from other labelled blocks:
    --  - we never shortcut a reference to a CAF to the contents of its
    --    SRT, since the point of SRTs is to keep CAFs alive.
    --  - CAFs therefore don't take part in the dependency analysis in depAnalSRTs.
    --    instead we generate their SRTs after everything else.
    getCAFs :: Platform -> CAFEnv -> [CmmDecl] -> [(Label, CAFLabel, Set CAFLabel)]
    getCAFs platform cafEnv decls =
      [ (g_entry g, mkCAFLabel platform topLbl, cafs)
      | CmmProc top_info topLbl _ g <- decls
      , Just info <- [mapLookup (g_entry g) (info_tbls top_info)]
      , let rep = cit_rep info
      , isStaticRep rep && isThunkRep rep
      , Just cafs <- [mapLookup (g_entry g) cafEnv]
      ]

    -- | Get the list of blocks that correspond to the entry points for
    -- FUN_STATIC closures.  These are the blocks for which if we have an
    -- SRT we can merge it with the static closure. [FUN]
    getStaticFuns :: [CmmDecl] -> [(BlockId, CLabel)]
    getStaticFuns decls =
      [ (g_entry g, lbl)
      | CmmProc top_info _ _ g <- decls
      , Just info <- [mapLookup (g_entry g) (info_tbls top_info)]
      , Just (id, _) <- [cit_clo info]
      , let rep = cit_rep info
      , isStaticRep rep && isFunRep rep
      , let !lbl = mkLocalClosureLabel (idName id) (idCafInfo id)
      ]

    -- | Maps labels from 'cafAnal' to the final CLabel that will appear
    -- in the SRT.
    --   - closures with singleton SRTs resolve to their single entry
    --   - closures with larger SRTs map to the label for that SRT
    --   - CAFs must not map to anything!
    --   - if a labels maps to Nothing, we found that this label's SRT
    --     is empty, so we don't need to refer to it from other SRTs.
    type SRTMap = Map CAFLabel (Maybe SRTEntry)

    -- | Given 'SRTMap' of a module, returns the set of non-CAFFY names in the
    -- module.  Any 'Name's not in the set are CAFFY.
    srtMapNonCAFs :: SRTMap -> NonCaffySet
    srtMapNonCAFs srtMap =
        NonCaffySet $ mkNameSet (mapMaybe get_name (Map.toList srtMap))
      where
        get_name (CAFLabel l, Nothing) = hasHaskellName l
        get_name (_l, Just _srt_entry) = Nothing

    -- | resolve a CAFLabel to its SRTEntry using the SRTMap
    resolveCAF :: Platform -> SRTMap -> CAFLabel -> Maybe SRTEntry
    resolveCAF platform srtMap lbl@(CAFLabel l) =
        srtTrace "resolveCAF" ("l:" <+> pdoc platform l <+> "resolved:" <+> pdoc platform ret) ret
      where
        ret = Map.findWithDefault (Just (SRTEntry (toClosureLbl platform l))) lbl srtMap

    -- | Attach SRTs to all info tables in the CmmDecls, and add SRT
    -- declarations to the ModuleSRTInfo.
    --
    doSRTs
      :: DynFlags
      -> ModuleSRTInfo
      -> [(CAFEnv, [CmmDecl])]
      -> [(CAFSet, CmmDecl)]
      -> IO (ModuleSRTInfo, [CmmDeclSRTs])

    doSRTs dflags moduleSRTInfo procs data_ = do
      us <- mkSplitUniqSupply 'u'

      let profile = targetProfile dflags

      -- Ignore the original grouping of decls, and combine all the
      -- CAFEnvs into a single CAFEnv.
      let static_data_env :: DataCAFEnv
          static_data_env =
            Map.fromList $
            flip map data_ $
            \(set, decl) ->
              case decl of
                CmmProc{} ->
                  pprPanic "doSRTs" (text "Proc in static data list:" <+> pdoc platform decl)
                CmmData _ static ->
                  case static of
                    CmmStatics lbl _ _ _ -> (lbl, set)
                    CmmStaticsRaw lbl _ -> (lbl, set)

          (proc_envs, procss) = unzip procs
          cafEnv = mapUnions proc_envs
          decls = map snd data_ ++ concat procss
          staticFuns = mapFromList (getStaticFuns decls)

          platform = targetPlatform dflags

      -- Put the decls in dependency order. Why? So that we can implement
      -- [Inline] and [Filter].  If we need to refer to an SRT that has
      -- a single entry, we use the entry itself, which means that we
      -- don't need to generate the singleton SRT in the first place.  But
      -- to do this we need to process blocks before things that depend on
      -- them.
      let
        sccs :: [SCC (SomeLabel, CAFLabel, Set CAFLabel)]
        sccs = {-# SCC depAnalSRTs #-} depAnalSRTs platform cafEnv static_data_env decls

        cafsWithSRTs :: [(Label, CAFLabel, Set CAFLabel)]
        cafsWithSRTs = getCAFs platform cafEnv decls

      srtTraceM "doSRTs" (text "data:"            <+> pdoc platform data_ $$
                          text "procs:"           <+> pdoc platform procs $$
                          text "static_data_env:" <+> pdoc platform static_data_env $$
                          text "sccs:"            <+> pdoc platform sccs $$
                          text "cafsWithSRTs:"    <+> pdoc platform cafsWithSRTs)

      -- On each strongly-connected group of decls, construct the SRT
      -- closures and the SRT fields for info tables.
      let result ::
            [ ( [CmmDeclSRTs]          -- generated SRTs
              , [(Label, CLabel)]      -- SRT fields for info tables
              , [(Label, [SRTEntry])]  -- SRTs to attach to static functions
              , Bool                   -- Whether the group has CAF references
              ) ]

          (result, moduleSRTInfo') =
            initUs_ us $
            flip runStateT moduleSRTInfo $ do
              nonCAFs <- mapM (doSCC dflags staticFuns static_data_env) sccs
              cAFs <- forM cafsWithSRTs $ \(l, cafLbl, cafs) ->
                oneSRT dflags staticFuns [BlockLabel l] [cafLbl]
                       True{-is a CAF-} cafs static_data_env
              return (nonCAFs ++ cAFs)

          (srt_declss, pairs, funSRTs, has_caf_refs) = unzip4 result
          srt_decls = concat srt_declss

      -- Next, update the info tables with the SRTs
      let
        srtFieldMap = mapFromList (concat pairs)
        funSRTMap = mapFromList (concat funSRTs)
        has_caf_refs' = or has_caf_refs
        decls' =
          concatMap (updInfoSRTs profile srtFieldMap funSRTMap has_caf_refs') decls

      -- Finally update CafInfos for raw static literals (CmmStaticsRaw). Those are
      -- not analysed in oneSRT so we never add entries for them to the SRTMap.
      let srtMap_w_raws =
            foldl' (\(srtMap :: SRTMap) (_, decl) ->
                      case decl of
                        CmmData _ CmmStatics{} ->
                          -- already updated by oneSRT
                          srtMap
                        CmmData _ (CmmStaticsRaw lbl _)
                          | isIdLabel lbl && not (isTickyLabel lbl) ->
                              -- Raw data are not analysed by oneSRT and they can't
                              -- be CAFFY.
                              -- See Note [Ticky labels in SRT analysis] above for
                              -- why we exclude ticky labels here.
                              Map.insert (mkCAFLabel platform lbl) Nothing srtMap
                          | otherwise ->
                              -- Not an IdLabel, ignore
                              srtMap
                        CmmProc{} ->
                          pprPanic "doSRTs" (text "Found Proc in static data list:" <+> pdoc platform decl))
                   (moduleSRTMap moduleSRTInfo') data_

      return (moduleSRTInfo'{ moduleSRTMap = srtMap_w_raws }, srt_decls ++ decls')

    -- | Build the SRT for a strongly-connected component of blocks
    doSCC
      :: DynFlags
      -> LabelMap CLabel -- which blocks are static function entry points
      -> DataCAFEnv      -- ^ static data
      -> SCC (SomeLabel, CAFLabel, Set CAFLabel)
      -> StateT ModuleSRTInfo UniqSM
            ( [CmmDeclSRTs]          -- generated SRTs
            , [(Label, CLabel)]      -- SRT fields for info tables
            , [(Label, [SRTEntry])]  -- SRTs to attach to static functions
            , Bool                   -- Whether the group has CAF references
            )

    doSCC dflags staticFuns static_data_env (AcyclicSCC (l, cafLbl, cafs)) =
      oneSRT dflags staticFuns [l] [cafLbl] False cafs static_data_env

    doSCC dflags staticFuns static_data_env (CyclicSCC nodes) = do
      -- build a single SRT for the whole cycle, see Note [recursive SRTs]
      let (lbls, caf_lbls, cafsets) = unzip3 nodes
          cafs = Set.unions cafsets
      oneSRT dflags staticFuns lbls caf_lbls False cafs static_data_env

    {- Note [recursive SRTs]

    If the dependency analyser has found us a recursive group of
    declarations, then we build a single SRT for the whole group, on the
    grounds that everything in the group is reachable from everything
    else, so we lose nothing by having a single SRT.

    However, there are a couple of wrinkles to be aware of.

    * The Set CAFfyLabel for this SRT will contain labels in the group
      itself. The SRTMap will therefore not contain entries for these labels
      yet, so we can't turn them into SRTEntries using resolveCAF. BUT we
      can just remove recursive references from the Set CAFLabel before
      generating the SRT - the group SRT will consist of the union of the SRTs of
      each of group's constituents minus recursive references.

    * That is, EXCEPT for static function closures and static data constructor
      applications. For the same reason described in Note [No static object
      resurrection], we cannot omit references to static function closures and
      constructor applications.

      But, since we will merge the SRT with one of the static function
      closures (see [FUN]), we can omit references to *that* static
      function closure from the SRT.

    * Similarly, we must reintroduce recursive references to static data
      constructor applications into the group's SRT.
    -}

    -- | Build an SRT for a set of blocks
    oneSRT
      :: DynFlags
      -> LabelMap CLabel            -- which blocks are static function entry points
      -> [SomeLabel]                -- blocks in this set
      -> [CAFLabel]                 -- labels for those blocks
      -> Bool                       -- True <=> this SRT is for a CAF
      -> Set CAFLabel               -- SRT for this set
      -> DataCAFEnv                 -- Static data labels in this group
      -> StateT ModuleSRTInfo UniqSM
           ( [CmmDeclSRTs]                -- SRT objects we built
           , [(Label, CLabel)]            -- SRT fields for these blocks' itbls
           , [(Label, [SRTEntry])]        -- SRTs to attach to static functions
           , Bool                         -- Whether the group has CAF references
           )

    oneSRT dflags staticFuns lbls caf_lbls isCAF cafs static_data_env = do
      topSRT <- get

      let
        this_mod = thisModule topSRT
        config = initNCGConfig dflags this_mod
        profile = targetProfile dflags
        platform = profilePlatform profile
        srtMap = moduleSRTMap topSRT

        blockids = getBlockLabels lbls

        -- Can we merge this SRT with a FUN_STATIC closure?
        maybeFunClosure :: Maybe (CLabel, Label)
        otherFunLabels :: [CLabel]
        (maybeFunClosure, otherFunLabels) =
          case [ (l,b) | b <- blockids, Just l <- [mapLookup b staticFuns] ] of
            [] -> (Nothing, [])
            ((l,b):xs) -> (Just (l,b), map fst xs)

        -- Remove recursive references from the SRT as described in
        -- Note [recursive SRTs]. We carefully reintroduce references to static
        -- functions and data constructor applications below, as is necessary due
        -- to Note [No static object resurrection].
        nonRec :: Set CAFLabel
        nonRec = cafs `Set.difference` Set.fromList caf_lbls

        -- Resolve references to their SRT entries
        resolved :: [SRTEntry]
        resolved = mapMaybe (resolveCAF platform srtMap) (Set.toList nonRec)

        -- The set of all SRTEntries in SRTs that we refer to from here.
        allBelow =
          Set.unions [ lbls | caf <- resolved
                            , Just lbls <- [Map.lookup caf (flatSRTs topSRT)] ]

        -- Remove SRTEntries that are also in an SRT that we refer to.
        -- Implements the [Filter] optimisation.
        filtered0 = Set.fromList resolved `Set.difference` allBelow

      srtTraceM "oneSRT:"
         (text "srtMap:"          <+> pdoc platform srtMap $$
          text "nonRec:"          <+> pdoc platform nonRec $$
          text "lbls:"            <+> pdoc platform lbls $$
          text "caf_lbls:"        <+> pdoc platform caf_lbls $$
          text "static_data_env:" <+> pdoc platform static_data_env $$
          text "cafs:"            <+> pdoc platform cafs $$
          text "blockids:"        <+> ppr blockids $$
          text "maybeFunClosure:" <+> pdoc platform maybeFunClosure $$
          text "otherFunLabels:"  <+> pdoc platform otherFunLabels $$
          text "resolved:"        <+> pdoc platform resolved $$
          text "allBelow:"        <+> pdoc platform allBelow $$
          text "filtered0:"       <+> pdoc platform filtered0)

      let
        isStaticFun = isJust maybeFunClosure

        -- For a label without a closure (e.g. a continuation), we must
        -- update the SRTMap for the label to point to a closure. It's
        -- important that we don't do this for static functions or CAFs,
        -- see Note [Invalid optimisation: shortcutting].
        updateSRTMap :: Maybe SRTEntry -> StateT ModuleSRTInfo UniqSM ()
        updateSRTMap srtEntry =
          srtTrace "updateSRTMap"
            (pdoc platform srtEntry <+> "isCAF:" <+> ppr isCAF <+>
             "isStaticFun:" <+> ppr isStaticFun) $
          when (not isCAF && (not isStaticFun || isNothing srtEntry)) $
            modify' $ \state ->
               let !srt_map =
                     foldl' (\srt_map cafLbl@(CAFLabel clbl) ->
                              -- Only map static data to Nothing (== not CAFFY). For CAFFY
                              -- statics we refer to the static itself instead of a SRT.
                              if not (Map.member clbl static_data_env) || isNothing srtEntry then
                                Map.insert cafLbl srtEntry srt_map
                              else
                                srt_map)
                            (moduleSRTMap state)
                            caf_lbls
               in
                   state{ moduleSRTMap = srt_map }

        allStaticData =
          all (\(CAFLabel clbl) -> Map.member clbl static_data_env) caf_lbls

      if Set.null filtered0 then do
        srtTraceM "oneSRT: empty" (pdoc platform caf_lbls)
        updateSRTMap Nothing
        return ([], [], [], False)
      else do
        -- We're going to build an SRT for this group, which should include function
        -- references in the group. See Note [recursive SRTs].
        let allBelow_funs =
              Set.fromList (map (SRTEntry . toClosureLbl platform) otherFunLabels)
        -- We must also ensure that all CAFfy static data constructor applications
        -- are included. See Note [recursive SRTs] and #20959.
        let allBelow_data =
              Set.fromList
              [ SRTEntry $ toClosureLbl platform lbl
              | DeclLabel lbl <- lbls
              , Just refs <- pure $ Map.lookup lbl static_data_env
              , not $ Set.null refs
              ]
        let filtered = filtered0 `Set.union` allBelow_funs `Set.union` allBelow_data
        srtTraceM "oneSRT" (text "filtered:"      <+> pdoc platform filtered $$
                            text "allBelow_funs:" <+> pdoc platform allBelow_funs)
        case Set.toList filtered of
          [] -> pprPanic "oneSRT" empty -- unreachable

          -- [Inline] - when we have only one entry there is no need to
          -- build an SRT object at all, instead we put the singleton SRT
          -- entry in the info table.
          [one@(SRTEntry lbl)]
            | -- Info tables refer to SRTs by offset (as noted in the section
              -- "Referring to an SRT from the info table" of Note [SRTs]). However,
              -- when dynamic linking is used we cannot guarantee that the offset
              -- between the SRT and the info table will fit in the offset field.
              -- Consequently we build a singleton SRT in this case.
              not (labelDynamic config lbl)

              -- MachO relocations can't express offsets between compilation units at
              -- all, so we are always forced to build a singleton SRT in this case.
                && (not (osMachOTarget $ platformOS $ profilePlatform profile)
                   || isLocalCLabel this_mod lbl) -> do

              -- If we have a static function closure, then it becomes the
              -- SRT object, and everything else points to it. (the only way
              -- we could have multiple labels here is if this is a
              -- recursive group, see Note [recursive SRTs])
              case maybeFunClosure of
                Just (staticFunLbl,staticFunBlock) ->
                    return ([], withLabels, [], True)
                  where
                    withLabels =
                      [ (b, if b == staticFunBlock then lbl else staticFunLbl)
                      | b <- blockids ]
                Nothing -> do
                  srtTraceM "oneSRT: one" (text "caf_lbls:" <+> pdoc platform caf_lbls $$
                                           text "one:"      <+> pdoc platform one)
                  updateSRTMap (Just one)
                  return ([], map (,lbl) blockids, [], True)

          cafList | allStaticData ->
            return ([], [], [], not (null cafList))

          cafList ->
            -- Check whether an SRT with the same entries has been emitted already.
            -- Implements the [Common] optimisation.
            case Map.lookup filtered (dedupSRTs topSRT) of
              Just srtEntry@(SRTEntry srtLbl)  -> do
                srtTraceM "oneSRT [Common]" (pdoc platform caf_lbls <+> pdoc platform srtLbl)
                updateSRTMap (Just srtEntry)
                return ([], map (,srtLbl) blockids, [], True)
              Nothing -> do
                -- No duplicates: we have to build a new SRT object
                (decls, funSRTs, srtEntry) <-
                  case maybeFunClosure of
                    Just (fun,block) ->
                      return ( [], [(block, cafList)], SRTEntry fun )
                    Nothing -> do
                      (decls, entry) <- lift $ buildSRTChain profile cafList
                      return (decls, [], entry)
                updateSRTMap (Just srtEntry)
                let allBelowThis = Set.union allBelow filtered
                    newFlatSRTs = Map.insert srtEntry allBelowThis (flatSRTs topSRT)
                    -- When all definition in this group are static data we don't
                    -- generate any SRTs.
                    newDedupSRTs = Map.insert filtered srtEntry (dedupSRTs topSRT)
                modify' (\state -> state{ dedupSRTs = newDedupSRTs,
                                          flatSRTs = newFlatSRTs })
                srtTraceM "oneSRT: new" (text "caf_lbls:"      <+> pdoc platform caf_lbls $$
                                          text "filtered:"     <+> pdoc platform filtered $$
                                          text "srtEntry:"     <+> pdoc platform srtEntry $$
                                          text "newDedupSRTs:" <+> pdoc platform newDedupSRTs $$
                                          text "newFlatSRTs:"  <+> pdoc platform newFlatSRTs)
                let SRTEntry lbl = srtEntry
                return (decls, map (,lbl) blockids, funSRTs, True)

    -- | Build a static SRT object (or a chain of objects) from a list of
    -- SRTEntries.
    buildSRTChain
       :: Profile
       -> [SRTEntry]
       -> UniqSM
            ( [CmmDeclSRTs] -- The SRT object(s)
            , SRTEntry      -- label to use in the info table
            )
    buildSRTChain _ [] = panic "buildSRT: empty"
    buildSRTChain profile cafSet =
      case splitAt mAX_SRT_SIZE cafSet of
        (these, []) -> do
          (decl,lbl) <- buildSRT profile these
          return ([decl], lbl)
        (these,those) -> do
          (rest, rest_lbl) <- buildSRTChain profile (head these : those)
          (decl,lbl) <- buildSRT profile (rest_lbl : tail these)
          return (decl:rest, lbl)
      where
        mAX_SRT_SIZE = 16

    buildSRT :: Profile -> [SRTEntry] -> UniqSM (CmmDeclSRTs, SRTEntry)
    buildSRT profile refs = do
      id <- getUniqueM
      let
        lbl = mkSRTLabel id
        platform = profilePlatform profile
        srt_n_info = mkSRTInfoLabel (length refs)
        fields =
          mkStaticClosure profile srt_n_info dontCareCCS
            [ CmmLabel lbl | SRTEntry lbl <- refs ]
            [] -- no padding
            [mkIntCLit platform 0] -- link field
            [] -- no saved info
      return (mkDataLits (Section Data lbl) lbl fields, SRTEntry lbl)

    -- | Update info tables with references to their SRTs. Also generate
    -- static closures, splicing in SRT fields as necessary.
    updInfoSRTs
      :: Profile
      -> LabelMap CLabel               -- SRT labels for each block
      -> LabelMap [SRTEntry]           -- SRTs to merge into FUN_STATIC closures
      -> Bool                          -- Whether the CmmDecl's group has CAF references
      -> CmmDecl
      -> [CmmDeclSRTs]

    updInfoSRTs _ _ _ _ (CmmData s (CmmStaticsRaw lbl statics))
      = [CmmData s (CmmStaticsRaw lbl statics)]

    updInfoSRTs profile _ _ caffy (CmmData s (CmmStatics lbl itbl ccs payload))
      = [CmmData s (CmmStaticsRaw lbl (map CmmStaticLit field_lits))]
      where
        caf_info = if caffy then MayHaveCafRefs else NoCafRefs
        field_lits = mkStaticClosureFields profile itbl ccs caf_info payload

    updInfoSRTs profile srt_env funSRTEnv caffy (CmmProc top_info top_l live g)
      | Just (_,closure) <- maybeStaticClosure = [ proc, closure ]
      | otherwise = [ proc ]
      where
        caf_info = if caffy then MayHaveCafRefs else NoCafRefs
        proc = CmmProc top_info { info_tbls = newTopInfo } top_l live g
        newTopInfo = mapMapWithKey updInfoTbl (info_tbls top_info)
        updInfoTbl l info_tbl
          | l == g_entry g, Just (inf, _) <- maybeStaticClosure = inf
          | otherwise  = info_tbl { cit_srt = mapLookup l srt_env }

        -- Generate static closures [FUN].  Note that this also generates
        -- static closures for thunks (CAFs), because it's easier to treat
        -- them uniformly in the code generator.
        maybeStaticClosure :: Maybe (CmmInfoTable, CmmDeclSRTs)
        maybeStaticClosure
          | Just info_tbl@CmmInfoTable{..} <-
               mapLookup (g_entry g) (info_tbls top_info)
          , Just (id, ccs) <- cit_clo
          , isStaticRep cit_rep =
            let
              (newInfo, srtEntries) = case mapLookup (g_entry g) funSRTEnv of
                Nothing ->
                  -- if we don't add SRT entries to this closure, then we
                  -- want to set the srt field in its info table as usual
                  (info_tbl { cit_srt = mapLookup (g_entry g) srt_env }, [])
                Just srtEntries -> srtTrace "maybeStaticFun" (pdoc (profilePlatform profile) res)
                  (info_tbl { cit_rep = new_rep }, res)
                  where res = [ CmmLabel lbl | SRTEntry lbl <- srtEntries ]
              fields = mkStaticClosureFields profile info_tbl ccs caf_info srtEntries
              new_rep = case cit_rep of
                 HeapRep sta ptrs nptrs ty ->
                   HeapRep sta (ptrs + length srtEntries) nptrs ty
                 _other -> panic "maybeStaticFun"
              lbl = mkLocalClosureLabel (idName id) caf_info
            in
              Just (newInfo, mkDataLits (Section Data lbl) lbl fields)
          | otherwise = Nothing

    srtTrace :: String -> SDoc -> b -> b
    -- srtTrace = pprTrace
    srtTrace _ _ b = b

    srtTraceM :: Applicative f => String -> SDoc -> f ()
    srtTraceM str doc = srtTrace str doc (pure ())