GHC/Cmm/CLabel.hs

    -----------------------------------------------------------------------------
    --
    -- Object-file symbols (called CLabel for histerical raisins).
    --
    -- (c) The University of Glasgow 2004-2006
    --
    -----------------------------------------------------------------------------

    {-# LANGUAGE CPP #-}
    {-# LANGUAGE BangPatterns #-}
    {-# LANGUAGE LambdaCase #-}
    {-# LANGUAGE MultiParamTypeClasses #-}
    {-# LANGUAGE FlexibleInstances #-}

    module GHC.Cmm.CLabel (
            CLabel, -- abstract type
            NeedExternDecl (..),
            ForeignLabelSource(..),
            DynamicLinkerLabelInfo(..),
            ConInfoTableLocation(..),
            getConInfoTableLocation,

            -- * Constructors
            mkClosureLabel,
            mkSRTLabel,
            mkInfoTableLabel,
            mkEntryLabel,
            mkRednCountsLabel,
            mkConInfoTableLabel,
            mkApEntryLabel,
            mkApInfoTableLabel,
            mkClosureTableLabel,
            mkBytesLabel,

            mkLocalBlockLabel,
            mkLocalClosureLabel,
            mkLocalInfoTableLabel,
            mkLocalClosureTableLabel,

            mkBlockInfoTableLabel,

            mkBitmapLabel,
            mkStringLitLabel,

            mkAsmTempLabel,
            mkAsmTempDerivedLabel,
            mkAsmTempEndLabel,
            mkAsmTempProcEndLabel,
            mkAsmTempDieLabel,

            mkDirty_MUT_VAR_Label,
            mkNonmovingWriteBarrierEnabledLabel,
            mkUpdInfoLabel,
            mkBHUpdInfoLabel,
            mkIndStaticInfoLabel,
            mkMainCapabilityLabel,
            mkMAP_FROZEN_CLEAN_infoLabel,
            mkMAP_FROZEN_DIRTY_infoLabel,
            mkMAP_DIRTY_infoLabel,
            mkSMAP_FROZEN_CLEAN_infoLabel,
            mkSMAP_FROZEN_DIRTY_infoLabel,
            mkSMAP_DIRTY_infoLabel,
            mkBadAlignmentLabel,
            mkArrWords_infoLabel,
            mkSRTInfoLabel,

            mkTopTickyCtrLabel,
            mkCAFBlackHoleInfoTableLabel,
            mkRtsPrimOpLabel,
            mkRtsSlowFastTickyCtrLabel,

            mkSelectorInfoLabel,
            mkSelectorEntryLabel,
            mkCmmInfoLabel,
            mkCmmEntryLabel,
            mkCmmRetInfoLabel,
            mkCmmRetLabel,
            mkCmmCodeLabel,
            mkCmmDataLabel,
            mkRtsCmmDataLabel,
            mkCmmClosureLabel,
            mkRtsApFastLabel,
            mkPrimCallLabel,
            mkForeignLabel,
            mkCCLabel,
            mkCCSLabel,
            mkIPELabel,
            InfoProvEnt(..),

            mkDynamicLinkerLabel,
            mkPicBaseLabel,
            mkDeadStripPreventer,
            mkHpcTicksLabel,

            -- * Predicates
            hasCAF,
            needsCDecl,
            maybeLocalBlockLabel,
            externallyVisibleCLabel,
            isMathFun,
            isCFunctionLabel,
            isGcPtrLabel,
            labelDynamic,
            isLocalCLabel,
            mayRedirectTo,
            isInfoTableLabel,
            isConInfoTableLabel,
            isIdLabel,
            isTickyLabel,
            hasHaskellName,
            hasIdLabelInfo,
            isBytesLabel,
            isForeignLabel,
            isSomeRODataLabel,
            isStaticClosureLabel,

            -- * Conversions
            toClosureLbl,
            toSlowEntryLbl,
            toEntryLbl,
            toInfoLbl,

            -- * Pretty-printing
            LabelStyle (..),
            pprDebugCLabel,
            pprCLabel,
            ppInternalProcLabel,

            -- * Others
            dynamicLinkerLabelInfo,
            addLabelSize,
            foreignLabelStdcallInfo
        ) where

    #include "HsVersions.h"

    import GHC.Prelude

    import GHC.Types.Id.Info
    import GHC.Types.Basic
    import {-# SOURCE #-} GHC.Cmm.BlockId (BlockId, mkBlockId)
    import GHC.Unit.Types
    import GHC.Types.Name
    import GHC.Types.Unique
    import GHC.Builtin.PrimOps
    import GHC.Types.CostCentre
    import GHC.Utils.Outputable
    import GHC.Utils.Panic
    import GHC.Data.FastString
    import GHC.Driver.Session
    import GHC.Platform
    import GHC.Types.Unique.Set
    import GHC.Utils.Misc
    import GHC.Core.Ppr ( {- instances -} )
    import GHC.CmmToAsm.Config
    import GHC.Types.SrcLoc

    -- -----------------------------------------------------------------------------
    -- The CLabel type

    {- |
      'CLabel' is an abstract type that supports the following operations:

      - Pretty printing

      - In a C file, does it need to be declared before use?  (i.e. is it
        guaranteed to be already in scope in the places we need to refer to it?)

      - If it needs to be declared, what type (code or data) should it be
        declared to have?

      - Is it visible outside this object file or not?

      - Is it "dynamic" (see details below)

      - Eq and Ord, so that we can make sets of CLabels (currently only
        used in outputting C as far as I can tell, to avoid generating
        more than one declaration for any given label).

      - Converting an info table label into an entry label.

      CLabel usage is a bit messy in GHC as they are used in a number of different
      contexts:

      - By the C-- AST to identify labels

      - By the unregisterised C code generator (\"PprC\") for naming functions (hence
        the name 'CLabel')

      - By the native and LLVM code generators to identify labels

      For extra fun, each of these uses a slightly different subset of constructors
      (e.g. 'AsmTempLabel' and 'AsmTempDerivedLabel' are used only in the NCG and
      LLVM backends).

      In general, we use 'IdLabel' to represent Haskell things early in the
      pipeline. However, later optimization passes will often represent blocks they
      create with 'LocalBlockLabel' where there is no obvious 'Name' to hang off the
      label.
    -}

    data CLabel
      = -- | A label related to the definition of a particular Id or Con in a .hs file.
        IdLabel
            Name
            CafInfo
            IdLabelInfo             -- ^ encodes the suffix of the label

      -- | A label from a .cmm file that is not associated with a .hs level Id.
      | CmmLabel
            UnitId                  -- ^ what package the label belongs to.
            NeedExternDecl          -- ^ does the label need an "extern .." declaration
            FastString              -- ^ identifier giving the prefix of the label
            CmmLabelInfo            -- ^ encodes the suffix of the label

      -- | A label with a baked-in \/ algorithmically generated name that definitely
      --    comes from the RTS. The code for it must compile into libHSrts.a \/ libHSrts.so
      --    If it doesn't have an algorithmically generated name then use a CmmLabel
      --    instead and give it an appropriate UnitId argument.
      | RtsLabel
            RtsLabelInfo

      -- | A label associated with a block. These aren't visible outside of the
      -- compilation unit in which they are defined. These are generally used to
      -- name blocks produced by Cmm-to-Cmm passes and the native code generator,
      -- where we don't have a 'Name' to associate the label to and therefore can't
      -- use 'IdLabel'.
      | LocalBlockLabel
            {-# UNPACK #-} !Unique

      -- | A 'C' (or otherwise foreign) label.
      --
      | ForeignLabel
            FastString              -- ^ name of the imported label.

            (Maybe Int)             -- ^ possible '@n' suffix for stdcall functions
                                    -- When generating C, the '@n' suffix is omitted, but when
                                    -- generating assembler we must add it to the label.

            ForeignLabelSource      -- ^ what package the foreign label is in.

            FunctionOrData

      -- | Local temporary label used for native (or LLVM) code generation; must not
      -- appear outside of these contexts. Use primarily for debug information
      | AsmTempLabel
            {-# UNPACK #-} !Unique

      -- | A label \"derived\" from another 'CLabel' by the addition of a suffix.
      -- Must not occur outside of the NCG or LLVM code generators.
      | AsmTempDerivedLabel
            CLabel
            FastString              -- ^ suffix

      | StringLitLabel
            {-# UNPACK #-} !Unique

      | CC_Label  CostCentre
      | CCS_Label CostCentreStack
      | IPE_Label InfoProvEnt

      -- | These labels are generated and used inside the NCG only.
      --    They are special variants of a label used for dynamic linking
      --    see module "GHC.CmmToAsm.PIC" for details.
      | DynamicLinkerLabel DynamicLinkerLabelInfo CLabel

      -- | This label is generated and used inside the NCG only.
      --    It is used as a base for PIC calculations on some platforms.
      --    It takes the form of a local numeric assembler label '1'; and
      --    is pretty-printed as 1b, referring to the previous definition
      --    of 1: in the assembler source file.
      | PicBaseLabel

      -- | A label before an info table to prevent excessive dead-stripping on darwin
      | DeadStripPreventer CLabel

      -- | Per-module table of tick locations
      | HpcTicksLabel Module

      -- | Static reference table
      | SRTLabel
            {-# UNPACK #-} !Unique

      -- | A bitmap (function or case return)
      | LargeBitmapLabel
            {-# UNPACK #-} !Unique

      deriving Eq

    isIdLabel :: CLabel -> Bool
    isIdLabel IdLabel{} = True
    isIdLabel _ = False

    -- Used in SRT analysis. See Note [Ticky labels in SRT analysis] in
    -- GHC.Cmm.Info.Build.
    isTickyLabel :: CLabel -> Bool
    isTickyLabel (IdLabel _ _ RednCounts) = True
    isTickyLabel _ = False

    -- | Indicate if "GHC.CmmToC" has to generate an extern declaration for the
    -- label (e.g. "extern StgWordArray(foo)").  The type is fixed to StgWordArray.
    --
    -- Symbols from the RTS don't need "extern" declarations because they are
    -- exposed via "includes/Stg.h" with the appropriate type. See 'needsCDecl'.
    --
    -- The fixed StgWordArray type led to "conflicting types" issues with user
    -- provided Cmm files (not in the RTS) that declare data of another type (#15467
    -- and test for #17920).  Hence the Cmm parser considers that labels in data
    -- sections don't need the "extern" declaration (just add one explicitly if you
    -- need it).
    --
    -- See https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/compiler/backends/ppr-c#prototypes
    -- for why extern declaration are needed at all.
    newtype NeedExternDecl
       = NeedExternDecl Bool
       deriving (Ord,Eq)

    -- This is laborious, but necessary. We can't derive Ord because
    -- Unique doesn't have an Ord instance. Note nonDetCmpUnique in the
    -- implementation. See Note [No Ord for Unique]
    -- This is non-deterministic but we do not currently support deterministic
    -- code-generation. See Note [Unique Determinism and code generation]
    instance Ord CLabel where
      compare (IdLabel a1 b1 c1) (IdLabel a2 b2 c2) =
        compare a1 a2 `thenCmp`
        compare b1 b2 `thenCmp`
        compare c1 c2
      compare (CmmLabel a1 b1 c1 d1) (CmmLabel a2 b2 c2 d2) =
        compare a1 a2 `thenCmp`
        compare b1 b2 `thenCmp`
        uniqCompareFS c1 c2 `thenCmp`
        compare d1 d2
      compare (RtsLabel a1) (RtsLabel a2) = compare a1 a2
      compare (LocalBlockLabel u1) (LocalBlockLabel u2) = nonDetCmpUnique u1 u2
      compare (ForeignLabel a1 b1 c1 d1) (ForeignLabel a2 b2 c2 d2) =
        uniqCompareFS a1 a2 `thenCmp`
        compare b1 b2 `thenCmp`
        compare c1 c2 `thenCmp`
        compare d1 d2
      compare (AsmTempLabel u1) (AsmTempLabel u2) = nonDetCmpUnique u1 u2
      compare (AsmTempDerivedLabel a1 b1) (AsmTempDerivedLabel a2 b2) =
        compare a1 a2 `thenCmp`
        uniqCompareFS b1 b2
      compare (StringLitLabel u1) (StringLitLabel u2) =
        nonDetCmpUnique u1 u2
      compare (CC_Label a1) (CC_Label a2) =
        compare a1 a2
      compare (CCS_Label a1) (CCS_Label a2) =
        compare a1 a2
      compare (IPE_Label a1) (IPE_Label a2) =
        compare a1 a2
      compare (DynamicLinkerLabel a1 b1) (DynamicLinkerLabel a2 b2) =
        compare a1 a2 `thenCmp`
        compare b1 b2
      compare PicBaseLabel PicBaseLabel = EQ
      compare (DeadStripPreventer a1) (DeadStripPreventer a2) =
        compare a1 a2
      compare (HpcTicksLabel a1) (HpcTicksLabel a2) =
        compare a1 a2
      compare (SRTLabel u1) (SRTLabel u2) =
        nonDetCmpUnique u1 u2
      compare (LargeBitmapLabel u1) (LargeBitmapLabel u2) =
        nonDetCmpUnique u1 u2
      compare IdLabel{} _ = LT
      compare _ IdLabel{} = GT
      compare CmmLabel{} _ = LT
      compare _ CmmLabel{} = GT
      compare RtsLabel{} _ = LT
      compare _ RtsLabel{} = GT
      compare LocalBlockLabel{} _ = LT
      compare _ LocalBlockLabel{} = GT
      compare ForeignLabel{} _ = LT
      compare _ ForeignLabel{} = GT
      compare AsmTempLabel{} _ = LT
      compare _ AsmTempLabel{} = GT
      compare AsmTempDerivedLabel{} _ = LT
      compare _ AsmTempDerivedLabel{} = GT
      compare StringLitLabel{} _ = LT
      compare _ StringLitLabel{} = GT
      compare CC_Label{} _ = LT
      compare _ CC_Label{} = GT
      compare CCS_Label{} _ = LT
      compare _ CCS_Label{} = GT
      compare DynamicLinkerLabel{} _ = LT
      compare _ DynamicLinkerLabel{} = GT
      compare PicBaseLabel{} _ = LT
      compare _ PicBaseLabel{} = GT
      compare DeadStripPreventer{} _ = LT
      compare _ DeadStripPreventer{} = GT
      compare HpcTicksLabel{} _ = LT
      compare _ HpcTicksLabel{} = GT
      compare SRTLabel{} _ = LT
      compare _ SRTLabel{} = GT
      compare (IPE_Label {}) _ = LT
      compare  _ (IPE_Label{}) = GT

    -- | Record where a foreign label is stored.
    data ForeignLabelSource

       -- | Label is in a named package
       = ForeignLabelInPackage UnitId

       -- | Label is in some external, system package that doesn't also
       --   contain compiled Haskell code, and is not associated with any .hi files.
       --   We don't have to worry about Haskell code being inlined from
       --   external packages. It is safe to treat the RTS package as "external".
       | ForeignLabelInExternalPackage

       -- | Label is in the package currently being compiled.
       --   This is only used for creating hacky tmp labels during code generation.
       --   Don't use it in any code that might be inlined across a package boundary
       --   (ie, core code) else the information will be wrong relative to the
       --   destination module.
       | ForeignLabelInThisPackage

       deriving (Eq, Ord)

    -- | For debugging problems with the CLabel representation.
    --      We can't make a Show instance for CLabel because lots of its components don't have instances.
    --      The regular Outputable instance only shows the label name, and not its other info.
    --
    pprDebugCLabel :: Platform -> CLabel -> SDoc
    pprDebugCLabel platform lbl = pprCLabel platform AsmStyle lbl <> parens extra
       where
          extra = case lbl of
             IdLabel _ _ info
                -> text "IdLabel" <> whenPprDebug (text ":" <> ppr info)

             CmmLabel pkg _ext _name _info
                -> text "CmmLabel" <+> ppr pkg

             RtsLabel{}
                -> text "RtsLabel"

             ForeignLabel _name mSuffix src funOrData
                 -> text "ForeignLabel" <+> ppr mSuffix <+> ppr src <+> ppr funOrData

             _  -> text "other CLabel"

    data IdLabelInfo
      = Closure             -- ^ Label for closure
      | InfoTable           -- ^ Info tables for closures; always read-only
      | Entry               -- ^ Entry point
      | Slow                -- ^ Slow entry point

      | LocalInfoTable      -- ^ Like InfoTable but not externally visible
      | LocalEntry          -- ^ Like Entry but not externally visible

      | RednCounts          -- ^ Label of place to keep Ticky-ticky  info for this Id

      | ConEntry ConInfoTableLocation
      -- ^ Constructor entry point, when `-fdistinct-info-tables` is enabled then
      -- each usage of a constructor will be given a unique number and a fresh info
      -- table will be created in the module where the constructor is used. The
      -- argument is used to keep track of which info table a usage of a constructor
      -- should use. When the argument is 'Nothing' then it uses the info table which
      -- is defined in the module where the datatype is declared, this is the usual case.
      -- When it is (Just (m, k)) it will use the kth info table defined in module m. The
      -- point of this inefficiency is so that you can work out where allocations of data
      -- constructors are coming from when you are debugging.

      | ConInfoTable ConInfoTableLocation        -- ^ Corresponding info table

      | ClosureTable        -- ^ Table of closures for Enum tycons

      | Bytes               -- ^ Content of a string literal. See
                            -- Note [Bytes label].
      | BlockInfoTable      -- ^ Like LocalInfoTable but for a proc-point block
                            -- instead of a closure entry-point.
                            -- See Note [Proc-point local block entry-point].

      deriving (Eq, Ord)

    -- | Which module is the info table from, and which number was it.
    data ConInfoTableLocation = UsageSite Module Int
                              | DefinitionSite
                                  deriving (Eq, Ord)

    instance Outputable ConInfoTableLocation where
      ppr (UsageSite m n) = text "Loc(" <> ppr n <> text "):" <+> ppr m
      ppr DefinitionSite = empty

    getConInfoTableLocation :: IdLabelInfo -> Maybe ConInfoTableLocation
    getConInfoTableLocation (ConInfoTable ci) = Just ci
    getConInfoTableLocation _ = Nothing

    instance Outputable IdLabelInfo where
      ppr Closure    = text "Closure"
      ppr InfoTable  = text "InfoTable"
      ppr Entry      = text "Entry"
      ppr Slow       = text "Slow"

      ppr LocalInfoTable  = text "LocalInfoTable"
      ppr LocalEntry      = text "LocalEntry"

      ppr RednCounts      = text "RednCounts"
      ppr (ConEntry mn) = text "ConEntry" <+> ppr mn
      ppr (ConInfoTable mn) = text "ConInfoTable" <+> ppr mn
      ppr ClosureTable = text "ClosureTable"
      ppr Bytes        = text "Bytes"
      ppr BlockInfoTable  = text "BlockInfoTable"

    data RtsLabelInfo
      = RtsSelectorInfoTable Bool{-updatable-} Int{-offset-}  -- ^ Selector thunks
      | RtsSelectorEntry     Bool{-updatable-} Int{-offset-}

      | RtsApInfoTable       Bool{-updatable-} Int{-arity-}    -- ^ AP thunks
      | RtsApEntry           Bool{-updatable-} Int{-arity-}

      | RtsPrimOp            PrimOp
      | RtsApFast            NonDetFastString    -- ^ _fast versions of generic apply
      | RtsSlowFastTickyCtr String

      deriving (Eq,Ord)

    -- | What type of Cmm label we're dealing with.
    --      Determines the suffix appended to the name when a CLabel.CmmLabel
    --      is pretty printed.
    data CmmLabelInfo
      = CmmInfo                     -- ^ misc rts info tables,      suffix _info
      | CmmEntry                    -- ^ misc rts entry points,     suffix _entry
      | CmmRetInfo                  -- ^ misc rts ret info tables,  suffix _info
      | CmmRet                      -- ^ misc rts return points,    suffix _ret
      | CmmData                     -- ^ misc rts data bits, eg CHARLIKE_closure
      | CmmCode                     -- ^ misc rts code
      | CmmClosure                  -- ^ closures eg CHARLIKE_closure
      | CmmPrimCall                 -- ^ a prim call to some hand written Cmm code
      deriving (Eq, Ord)

    data DynamicLinkerLabelInfo
      = CodeStub                    -- MachO: Lfoo$stub, ELF: foo@plt
      | SymbolPtr                   -- MachO: Lfoo$non_lazy_ptr, Windows: __imp_foo
      | GotSymbolPtr                -- ELF: foo@got
      | GotSymbolOffset             -- ELF: foo@gotoff

      deriving (Eq, Ord)

    -- -----------------------------------------------------------------------------
    -- Constructing CLabels
    -- -----------------------------------------------------------------------------

    -- Constructing IdLabels
    -- These are always local:

    mkSRTLabel     :: Unique -> CLabel
    mkSRTLabel u = SRTLabel u

    mkRednCountsLabel :: Name -> CLabel
    mkRednCountsLabel name = IdLabel name NoCafRefs RednCounts  -- Note [ticky for LNE]

    -- These have local & (possibly) external variants:
    mkLocalClosureLabel      :: Name -> CafInfo -> CLabel
    mkLocalInfoTableLabel    :: Name -> CafInfo -> CLabel
    mkLocalClosureTableLabel :: Name -> CafInfo -> CLabel
    mkLocalClosureLabel   !name !c  = IdLabel name  c Closure
    mkLocalInfoTableLabel   name c  = IdLabel name  c LocalInfoTable
    mkLocalClosureTableLabel name c = IdLabel name  c ClosureTable

    mkClosureLabel              :: Name -> CafInfo -> CLabel
    mkInfoTableLabel            :: Name -> CafInfo -> CLabel
    mkEntryLabel                :: Name -> CafInfo -> CLabel
    mkClosureTableLabel         :: Name -> CafInfo -> CLabel
    mkConInfoTableLabel         :: Name -> ConInfoTableLocation -> CLabel
    mkBytesLabel                :: Name -> CLabel
    mkClosureLabel name         c     = IdLabel name c Closure
    mkInfoTableLabel name       c     = IdLabel name c InfoTable
    mkEntryLabel name           c     = IdLabel name c Entry
    mkClosureTableLabel name    c     = IdLabel name c ClosureTable
    -- Special case for the normal 'DefinitionSite' case so that the 'ConInfoTable' application can be floated to a CAF.
    mkConInfoTableLabel name DefinitionSite = IdLabel name NoCafRefs (ConInfoTable DefinitionSite)
    mkConInfoTableLabel name k = IdLabel name NoCafRefs (ConInfoTable k)
    mkBytesLabel name                 = IdLabel name NoCafRefs Bytes

    mkBlockInfoTableLabel :: Name -> CafInfo -> CLabel
    mkBlockInfoTableLabel name c = IdLabel name c BlockInfoTable
                                   -- See Note [Proc-point local block entry-point].

    -- Constructing Cmm Labels
    mkDirty_MUT_VAR_Label,
        mkNonmovingWriteBarrierEnabledLabel,
        mkUpdInfoLabel,
        mkBHUpdInfoLabel, mkIndStaticInfoLabel, mkMainCapabilityLabel,
        mkMAP_FROZEN_CLEAN_infoLabel, mkMAP_FROZEN_DIRTY_infoLabel,
        mkMAP_DIRTY_infoLabel,
        mkArrWords_infoLabel,
        mkTopTickyCtrLabel,
        mkCAFBlackHoleInfoTableLabel,
        mkSMAP_FROZEN_CLEAN_infoLabel, mkSMAP_FROZEN_DIRTY_infoLabel,
        mkSMAP_DIRTY_infoLabel, mkBadAlignmentLabel :: CLabel
    mkDirty_MUT_VAR_Label           = mkForeignLabel (fsLit "dirty_MUT_VAR") Nothing ForeignLabelInExternalPackage IsFunction
    mkNonmovingWriteBarrierEnabledLabel
                                    = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "nonmoving_write_barrier_enabled") CmmData
    mkUpdInfoLabel                  = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_upd_frame")         CmmInfo
    mkBHUpdInfoLabel                = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_bh_upd_frame" )     CmmInfo
    mkIndStaticInfoLabel            = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_IND_STATIC")        CmmInfo
    mkMainCapabilityLabel           = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "MainCapability")        CmmData
    mkMAP_FROZEN_CLEAN_infoLabel    = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_MUT_ARR_PTRS_FROZEN_CLEAN") CmmInfo
    mkMAP_FROZEN_DIRTY_infoLabel    = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_MUT_ARR_PTRS_FROZEN_DIRTY") CmmInfo
    mkMAP_DIRTY_infoLabel           = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_MUT_ARR_PTRS_DIRTY") CmmInfo
    mkTopTickyCtrLabel              = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "top_ct")                CmmData
    mkCAFBlackHoleInfoTableLabel    = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_CAF_BLACKHOLE")     CmmInfo
    mkArrWords_infoLabel            = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_ARR_WORDS")         CmmInfo
    mkSMAP_FROZEN_CLEAN_infoLabel   = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_SMALL_MUT_ARR_PTRS_FROZEN_CLEAN") CmmInfo
    mkSMAP_FROZEN_DIRTY_infoLabel   = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_SMALL_MUT_ARR_PTRS_FROZEN_DIRTY") CmmInfo
    mkSMAP_DIRTY_infoLabel          = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_SMALL_MUT_ARR_PTRS_DIRTY") CmmInfo
    mkBadAlignmentLabel             = CmmLabel rtsUnitId (NeedExternDecl False) (fsLit "stg_badAlignment")      CmmEntry

    mkSRTInfoLabel :: Int -> CLabel
    mkSRTInfoLabel n = CmmLabel rtsUnitId (NeedExternDecl False) lbl CmmInfo
     where
       lbl =
         case n of
           1 -> fsLit "stg_SRT_1"
           2 -> fsLit "stg_SRT_2"
           3 -> fsLit "stg_SRT_3"
           4 -> fsLit "stg_SRT_4"
           5 -> fsLit "stg_SRT_5"
           6 -> fsLit "stg_SRT_6"
           7 -> fsLit "stg_SRT_7"
           8 -> fsLit "stg_SRT_8"
           9 -> fsLit "stg_SRT_9"
           10 -> fsLit "stg_SRT_10"
           11 -> fsLit "stg_SRT_11"
           12 -> fsLit "stg_SRT_12"
           13 -> fsLit "stg_SRT_13"
           14 -> fsLit "stg_SRT_14"
           15 -> fsLit "stg_SRT_15"
           16 -> fsLit "stg_SRT_16"
           _ -> panic "mkSRTInfoLabel"

    -----
    mkCmmInfoLabel,   mkCmmEntryLabel, mkCmmRetInfoLabel, mkCmmRetLabel,
      mkCmmCodeLabel, mkCmmClosureLabel
            :: UnitId -> FastString -> CLabel

    mkCmmDataLabel    :: UnitId -> NeedExternDecl -> FastString -> CLabel
    mkRtsCmmDataLabel :: FastString -> CLabel

    mkCmmInfoLabel       pkg str     = CmmLabel pkg (NeedExternDecl True) str CmmInfo
    mkCmmEntryLabel      pkg str     = CmmLabel pkg (NeedExternDecl True) str CmmEntry
    mkCmmRetInfoLabel    pkg str     = CmmLabel pkg (NeedExternDecl True) str CmmRetInfo
    mkCmmRetLabel        pkg str     = CmmLabel pkg (NeedExternDecl True) str CmmRet
    mkCmmCodeLabel       pkg str     = CmmLabel pkg (NeedExternDecl True) str CmmCode
    mkCmmClosureLabel    pkg str     = CmmLabel pkg (NeedExternDecl True) str CmmClosure
    mkCmmDataLabel       pkg ext str = CmmLabel pkg ext  str CmmData
    mkRtsCmmDataLabel    str         = CmmLabel rtsUnitId (NeedExternDecl False)  str CmmData
                                        -- RTS symbols don't need "GHC.CmmToC" to
                                        -- generate \"extern\" declaration (they are
                                        -- exposed via includes/Stg.h)

    mkLocalBlockLabel :: Unique -> CLabel
    mkLocalBlockLabel u = LocalBlockLabel u

    -- Constructing RtsLabels
    mkRtsPrimOpLabel :: PrimOp -> CLabel
    mkRtsPrimOpLabel primop = RtsLabel (RtsPrimOp primop)

    mkSelectorInfoLabel :: Platform -> Bool -> Int -> CLabel
    mkSelectorInfoLabel platform upd offset =
       ASSERT(offset >= 0 && offset <= pc_MAX_SPEC_SELECTEE_SIZE (platformConstants platform))
       RtsLabel (RtsSelectorInfoTable upd offset)

    mkSelectorEntryLabel :: Platform -> Bool -> Int -> CLabel
    mkSelectorEntryLabel platform upd offset =
       ASSERT(offset >= 0 && offset <= pc_MAX_SPEC_SELECTEE_SIZE (platformConstants platform))
       RtsLabel (RtsSelectorEntry upd offset)

    mkApInfoTableLabel :: Platform -> Bool -> Int -> CLabel
    mkApInfoTableLabel platform upd arity =
       ASSERT(arity > 0 && arity <= pc_MAX_SPEC_AP_SIZE (platformConstants platform))
       RtsLabel (RtsApInfoTable upd arity)

    mkApEntryLabel :: Platform -> Bool -> Int -> CLabel
    mkApEntryLabel platform upd arity =
       ASSERT(arity > 0 && arity <= pc_MAX_SPEC_AP_SIZE (platformConstants platform))
       RtsLabel (RtsApEntry upd arity)

    -- A call to some primitive hand written Cmm code
    mkPrimCallLabel :: PrimCall -> CLabel
    mkPrimCallLabel (PrimCall str pkg)
            = CmmLabel (toUnitId pkg) (NeedExternDecl True) str CmmPrimCall

    -- Constructing ForeignLabels

    -- | Make a foreign label
    mkForeignLabel
            :: FastString           -- name
            -> Maybe Int            -- size prefix
            -> ForeignLabelSource   -- what package it's in
            -> FunctionOrData
            -> CLabel

    mkForeignLabel = ForeignLabel

    -- | Update the label size field in a ForeignLabel
    addLabelSize :: CLabel -> Int -> CLabel
    addLabelSize (ForeignLabel str _ src  fod) sz
        = ForeignLabel str (Just sz) src fod
    addLabelSize label _
        = label

    -- | Whether label is a top-level string literal
    isBytesLabel :: CLabel -> Bool
    isBytesLabel (IdLabel _ _ Bytes) = True
    isBytesLabel _lbl = False

    -- | Whether label is a non-haskell label (defined in C code)
    isForeignLabel :: CLabel -> Bool
    isForeignLabel (ForeignLabel _ _ _ _) = True
    isForeignLabel _lbl = False

    -- | Whether label is a static closure label (can come from haskell or cmm)
    isStaticClosureLabel :: CLabel -> Bool
    -- Closure defined in haskell (.hs)
    isStaticClosureLabel (IdLabel _ _ Closure) = True
    -- Closure defined in cmm
    isStaticClosureLabel (CmmLabel _ _ _ CmmClosure) = True
    isStaticClosureLabel _lbl = False

    -- | Whether label is a .rodata label
    isSomeRODataLabel :: CLabel -> Bool
    -- info table defined in haskell (.hs)
    isSomeRODataLabel (IdLabel _ _ ClosureTable) = True
    isSomeRODataLabel (IdLabel _ _ ConInfoTable {}) = True
    isSomeRODataLabel (IdLabel _ _ InfoTable) = True
    isSomeRODataLabel (IdLabel _ _ LocalInfoTable) = True
    isSomeRODataLabel (IdLabel _ _ BlockInfoTable) = True
    -- info table defined in cmm (.cmm)
    isSomeRODataLabel (CmmLabel _ _ _ CmmInfo) = True
    isSomeRODataLabel _lbl = False

    -- | Whether label is points to some kind of info table
    isInfoTableLabel :: CLabel -> Bool
    isInfoTableLabel (IdLabel _ _ InfoTable)      = True
    isInfoTableLabel (IdLabel _ _ LocalInfoTable) = True
    isInfoTableLabel (IdLabel _ _ ConInfoTable {})   = True
    isInfoTableLabel (IdLabel _ _ BlockInfoTable) = True
    isInfoTableLabel _                            = False

    -- | Whether label is points to constructor info table
    isConInfoTableLabel :: CLabel -> Bool
    isConInfoTableLabel (IdLabel _ _ ConInfoTable {})   = True
    isConInfoTableLabel _                            = False

    -- | Get the label size field from a ForeignLabel
    foreignLabelStdcallInfo :: CLabel -> Maybe Int
    foreignLabelStdcallInfo (ForeignLabel _ info _ _) = info
    foreignLabelStdcallInfo _lbl = Nothing

    -- Constructing Large*Labels
    mkBitmapLabel   :: Unique -> CLabel
    mkBitmapLabel   uniq            = LargeBitmapLabel uniq

    -- | Info Table Provenance Entry
    -- See Note [Mapping Info Tables to Source Positions]
    data InfoProvEnt = InfoProvEnt
                                   { infoTablePtr :: !CLabel
                                   -- Address of the info table
                                   , infoProvEntClosureType :: !Int
                                   -- The closure type of the info table (from ClosureMacros.h)
                                   , infoTableType :: !String
                                   -- The rendered Haskell type of the closure the table represents
                                   , infoProvModule :: !Module
                                   -- Origin module
                                   , infoTableProv :: !(Maybe (RealSrcSpan, String)) }
                                   -- Position and information about the info table
                                   deriving (Eq, Ord)

    -- Constructing Cost Center Labels
    mkCCLabel  :: CostCentre      -> CLabel
    mkCCSLabel :: CostCentreStack -> CLabel
    mkIPELabel :: InfoProvEnt -> CLabel
    mkCCLabel           cc          = CC_Label cc
    mkCCSLabel          ccs         = CCS_Label ccs
    mkIPELabel          ipe         = IPE_Label ipe

    mkRtsApFastLabel :: FastString -> CLabel
    mkRtsApFastLabel str = RtsLabel (RtsApFast (NonDetFastString str))

    mkRtsSlowFastTickyCtrLabel :: String -> CLabel
    mkRtsSlowFastTickyCtrLabel pat = RtsLabel (RtsSlowFastTickyCtr pat)

    -- Constructing Code Coverage Labels
    mkHpcTicksLabel :: Module -> CLabel
    mkHpcTicksLabel                = HpcTicksLabel

    -- Constructing labels used for dynamic linking
    mkDynamicLinkerLabel :: DynamicLinkerLabelInfo -> CLabel -> CLabel
    mkDynamicLinkerLabel            = DynamicLinkerLabel

    dynamicLinkerLabelInfo :: CLabel -> Maybe (DynamicLinkerLabelInfo, CLabel)
    dynamicLinkerLabelInfo (DynamicLinkerLabel info lbl) = Just (info, lbl)
    dynamicLinkerLabelInfo _        = Nothing

    mkPicBaseLabel :: CLabel
    mkPicBaseLabel                  = PicBaseLabel

    -- Constructing miscellaneous other labels
    mkDeadStripPreventer :: CLabel -> CLabel
    mkDeadStripPreventer lbl        = DeadStripPreventer lbl

    mkStringLitLabel :: Unique -> CLabel
    mkStringLitLabel                = StringLitLabel

    mkAsmTempLabel :: Uniquable a => a -> CLabel
    mkAsmTempLabel a                = AsmTempLabel (getUnique a)

    mkAsmTempDerivedLabel :: CLabel -> FastString -> CLabel
    mkAsmTempDerivedLabel = AsmTempDerivedLabel

    mkAsmTempEndLabel :: CLabel -> CLabel
    mkAsmTempEndLabel l = mkAsmTempDerivedLabel l (fsLit "_end")

    -- | A label indicating the end of a procedure.
    mkAsmTempProcEndLabel :: CLabel -> CLabel
    mkAsmTempProcEndLabel l = mkAsmTempDerivedLabel l (fsLit "_proc_end")

    -- | Construct a label for a DWARF Debug Information Entity (DIE)
    -- describing another symbol.
    mkAsmTempDieLabel :: CLabel -> CLabel
    mkAsmTempDieLabel l = mkAsmTempDerivedLabel l (fsLit "_die")

    -- -----------------------------------------------------------------------------
    -- Convert between different kinds of label

    toClosureLbl :: Platform -> CLabel -> CLabel
    toClosureLbl platform lbl = case lbl of
       IdLabel n c _        -> IdLabel n c Closure
       CmmLabel m ext str _ -> CmmLabel m ext str CmmClosure
       _                    -> pprPanic "toClosureLbl" (pprDebugCLabel platform lbl)

    toSlowEntryLbl :: Platform -> CLabel -> CLabel
    toSlowEntryLbl platform lbl = case lbl of
       IdLabel n _ BlockInfoTable -> pprPanic "toSlowEntryLbl" (ppr n)
       IdLabel n c _              -> IdLabel n c Slow
       _                          -> pprPanic "toSlowEntryLbl" (pprDebugCLabel platform lbl)

    toEntryLbl :: Platform -> CLabel -> CLabel
    toEntryLbl platform lbl = case lbl of
       IdLabel n c LocalInfoTable    -> IdLabel n c LocalEntry
       IdLabel n c (ConInfoTable k)  -> IdLabel n c (ConEntry k)

       IdLabel n _ BlockInfoTable    -> mkLocalBlockLabel (nameUnique n)
                       -- See Note [Proc-point local block entry-point].
       IdLabel n c _                 -> IdLabel n c Entry
       CmmLabel m ext str CmmInfo    -> CmmLabel m ext str CmmEntry
       CmmLabel m ext str CmmRetInfo -> CmmLabel m ext str CmmRet
       _                             -> pprPanic "toEntryLbl" (pprDebugCLabel platform lbl)

    toInfoLbl :: Platform -> CLabel -> CLabel
    toInfoLbl platform lbl = case lbl of
       IdLabel n c LocalEntry      -> IdLabel n c LocalInfoTable
       IdLabel n c (ConEntry k)    -> IdLabel n c (ConInfoTable k)

       IdLabel n c _               -> IdLabel n c InfoTable
       CmmLabel m ext str CmmEntry -> CmmLabel m ext str CmmInfo
       CmmLabel m ext str CmmRet   -> CmmLabel m ext str CmmRetInfo
       _                           -> pprPanic "CLabel.toInfoLbl" (pprDebugCLabel platform lbl)

    hasHaskellName :: CLabel -> Maybe Name
    hasHaskellName (IdLabel n _ _) = Just n
    hasHaskellName _               = Nothing

    hasIdLabelInfo :: CLabel -> Maybe IdLabelInfo
    hasIdLabelInfo (IdLabel _ _ l) = Just l
    hasIdLabelInfo _ = Nothing

    -- -----------------------------------------------------------------------------
    -- Does a CLabel's referent itself refer to a CAF?
    hasCAF :: CLabel -> Bool
    hasCAF (IdLabel _ _ RednCounts) = False -- Note [ticky for LNE]
    hasCAF (IdLabel _ MayHaveCafRefs _) = True
    hasCAF _                            = False

    -- Note [ticky for LNE]
    -- ~~~~~~~~~~~~~~~~~~~~~

    -- Until 14 Feb 2013, every ticky counter was associated with a
    -- closure. Thus, ticky labels used IdLabel. It is odd that
    -- GHC.Cmm.Info.Build.cafTransfers would consider such a ticky label
    -- reason to add the name to the CAFEnv (and thus eventually the SRT),
    -- but it was harmless because the ticky was only used if the closure
    -- was also.
    --
    -- Since we now have ticky counters for LNEs, it is no longer the case
    -- that every ticky counter has an actual closure. So I changed the
    -- generation of ticky counters' CLabels to not result in their
    -- associated id ending up in the SRT.
    --
    -- NB IdLabel is still appropriate for ticky ids (as opposed to
    -- CmmLabel) because the LNE's counter is still related to an .hs Id,
    -- that Id just isn't for a proper closure.

    -- -----------------------------------------------------------------------------
    -- Does a CLabel need declaring before use or not?
    --
    -- See wiki:commentary/compiler/backends/ppr-c#prototypes

    needsCDecl :: CLabel -> Bool
      -- False <=> it's pre-declared; don't bother
      -- don't bother declaring Bitmap labels, we always make sure
      -- they are defined before use.
    needsCDecl (SRTLabel _)                 = True
    needsCDecl (LargeBitmapLabel _)         = False
    needsCDecl (IdLabel _ _ _)              = True
    needsCDecl (LocalBlockLabel _)          = True

    needsCDecl (StringLitLabel _)           = False
    needsCDecl (AsmTempLabel _)             = False
    needsCDecl (AsmTempDerivedLabel _ _)    = False
    needsCDecl (RtsLabel _)                 = False

    needsCDecl (CmmLabel pkgId (NeedExternDecl external) _ _)
            -- local labels mustn't have it
            | not external                  = False

            -- Prototypes for labels defined in the runtime system are imported
            --      into HC files via includes/Stg.h.
            | pkgId == rtsUnitId            = False

            -- For other labels we inline one into the HC file directly.
            | otherwise                     = True

    needsCDecl l@(ForeignLabel{})           = not (isMathFun l)
    needsCDecl (CC_Label _)                 = True
    needsCDecl (CCS_Label _)                = True
    needsCDecl (IPE_Label {})               = True
    needsCDecl (HpcTicksLabel _)            = True
    needsCDecl (DynamicLinkerLabel {})      = panic "needsCDecl DynamicLinkerLabel"
    needsCDecl PicBaseLabel                 = panic "needsCDecl PicBaseLabel"
    needsCDecl (DeadStripPreventer {})      = panic "needsCDecl DeadStripPreventer"

    -- | If a label is a local block label then return just its 'BlockId', otherwise
    -- 'Nothing'.
    maybeLocalBlockLabel :: CLabel -> Maybe BlockId
    maybeLocalBlockLabel (LocalBlockLabel uq)  = Just $ mkBlockId uq
    maybeLocalBlockLabel _                     = Nothing

    -- | Check whether a label corresponds to a C function that has
    --      a prototype in a system header somewhere, or is built-in
    --      to the C compiler. For these labels we avoid generating our
    --      own C prototypes.
    isMathFun :: CLabel -> Bool
    isMathFun (ForeignLabel fs _ _ _)       = fs `elementOfUniqSet` math_funs
    isMathFun _ = False

    math_funs :: UniqSet FastString
    math_funs = mkUniqSet [
            -- _ISOC99_SOURCE
            (fsLit "acos"),         (fsLit "acosf"),        (fsLit "acosh"),
            (fsLit "acoshf"),       (fsLit "acoshl"),       (fsLit "acosl"),
            (fsLit "asin"),         (fsLit "asinf"),        (fsLit "asinl"),
            (fsLit "asinh"),        (fsLit "asinhf"),       (fsLit "asinhl"),
            (fsLit "atan"),         (fsLit "atanf"),        (fsLit "atanl"),
            (fsLit "atan2"),        (fsLit "atan2f"),       (fsLit "atan2l"),
            (fsLit "atanh"),        (fsLit "atanhf"),       (fsLit "atanhl"),
            (fsLit "cbrt"),         (fsLit "cbrtf"),        (fsLit "cbrtl"),
            (fsLit "ceil"),         (fsLit "ceilf"),        (fsLit "ceill"),
            (fsLit "copysign"),     (fsLit "copysignf"),    (fsLit "copysignl"),
            (fsLit "cos"),          (fsLit "cosf"),         (fsLit "cosl"),
            (fsLit "cosh"),         (fsLit "coshf"),        (fsLit "coshl"),
            (fsLit "erf"),          (fsLit "erff"),         (fsLit "erfl"),
            (fsLit "erfc"),         (fsLit "erfcf"),        (fsLit "erfcl"),
            (fsLit "exp"),          (fsLit "expf"),         (fsLit "expl"),
            (fsLit "exp2"),         (fsLit "exp2f"),        (fsLit "exp2l"),
            (fsLit "expm1"),        (fsLit "expm1f"),       (fsLit "expm1l"),
            (fsLit "fabs"),         (fsLit "fabsf"),        (fsLit "fabsl"),
            (fsLit "fdim"),         (fsLit "fdimf"),        (fsLit "fdiml"),
            (fsLit "floor"),        (fsLit "floorf"),       (fsLit "floorl"),
            (fsLit "fma"),          (fsLit "fmaf"),         (fsLit "fmal"),
            (fsLit "fmax"),         (fsLit "fmaxf"),        (fsLit "fmaxl"),
            (fsLit "fmin"),         (fsLit "fminf"),        (fsLit "fminl"),
            (fsLit "fmod"),         (fsLit "fmodf"),        (fsLit "fmodl"),
            (fsLit "frexp"),        (fsLit "frexpf"),       (fsLit "frexpl"),
            (fsLit "hypot"),        (fsLit "hypotf"),       (fsLit "hypotl"),
            (fsLit "ilogb"),        (fsLit "ilogbf"),       (fsLit "ilogbl"),
            (fsLit "ldexp"),        (fsLit "ldexpf"),       (fsLit "ldexpl"),
            (fsLit "lgamma"),       (fsLit "lgammaf"),      (fsLit "lgammal"),
            (fsLit "llrint"),       (fsLit "llrintf"),      (fsLit "llrintl"),
            (fsLit "llround"),      (fsLit "llroundf"),     (fsLit "llroundl"),
            (fsLit "log"),          (fsLit "logf"),         (fsLit "logl"),
            (fsLit "log10l"),       (fsLit "log10"),        (fsLit "log10f"),
            (fsLit "log1pl"),       (fsLit "log1p"),        (fsLit "log1pf"),
            (fsLit "log2"),         (fsLit "log2f"),        (fsLit "log2l"),
            (fsLit "logb"),         (fsLit "logbf"),        (fsLit "logbl"),
            (fsLit "lrint"),        (fsLit "lrintf"),       (fsLit "lrintl"),
            (fsLit "lround"),       (fsLit "lroundf"),      (fsLit "lroundl"),
            (fsLit "modf"),         (fsLit "modff"),        (fsLit "modfl"),
            (fsLit "nan"),          (fsLit "nanf"),         (fsLit "nanl"),
            (fsLit "nearbyint"),    (fsLit "nearbyintf"),   (fsLit "nearbyintl"),
            (fsLit "nextafter"),    (fsLit "nextafterf"),   (fsLit "nextafterl"),
            (fsLit "nexttoward"),   (fsLit "nexttowardf"),  (fsLit "nexttowardl"),
            (fsLit "pow"),          (fsLit "powf"),         (fsLit "powl"),
            (fsLit "remainder"),    (fsLit "remainderf"),   (fsLit "remainderl"),
            (fsLit "remquo"),       (fsLit "remquof"),      (fsLit "remquol"),
            (fsLit "rint"),         (fsLit "rintf"),        (fsLit "rintl"),
            (fsLit "round"),        (fsLit "roundf"),       (fsLit "roundl"),
            (fsLit "scalbln"),      (fsLit "scalblnf"),     (fsLit "scalblnl"),
            (fsLit "scalbn"),       (fsLit "scalbnf"),      (fsLit "scalbnl"),
            (fsLit "sin"),          (fsLit "sinf"),         (fsLit "sinl"),
            (fsLit "sinh"),         (fsLit "sinhf"),        (fsLit "sinhl"),
            (fsLit "sqrt"),         (fsLit "sqrtf"),        (fsLit "sqrtl"),
            (fsLit "tan"),          (fsLit "tanf"),         (fsLit "tanl"),
            (fsLit "tanh"),         (fsLit "tanhf"),        (fsLit "tanhl"),
            (fsLit "tgamma"),       (fsLit "tgammaf"),      (fsLit "tgammal"),
            (fsLit "trunc"),        (fsLit "truncf"),       (fsLit "truncl"),
            -- ISO C 99 also defines these function-like macros in math.h:
            -- fpclassify, isfinite, isinf, isnormal, signbit, isgreater,
            -- isgreaterequal, isless, islessequal, islessgreater, isunordered

            -- additional symbols from _BSD_SOURCE
            (fsLit "drem"),         (fsLit "dremf"),        (fsLit "dreml"),
            (fsLit "finite"),       (fsLit "finitef"),      (fsLit "finitel"),
            (fsLit "gamma"),        (fsLit "gammaf"),       (fsLit "gammal"),
            (fsLit "isinf"),        (fsLit "isinff"),       (fsLit "isinfl"),
            (fsLit "isnan"),        (fsLit "isnanf"),       (fsLit "isnanl"),
            (fsLit "j0"),           (fsLit "j0f"),          (fsLit "j0l"),
            (fsLit "j1"),           (fsLit "j1f"),          (fsLit "j1l"),
            (fsLit "jn"),           (fsLit "jnf"),          (fsLit "jnl"),
            (fsLit "lgamma_r"),     (fsLit "lgammaf_r"),    (fsLit "lgammal_r"),
            (fsLit "scalb"),        (fsLit "scalbf"),       (fsLit "scalbl"),
            (fsLit "significand"),  (fsLit "significandf"), (fsLit "significandl"),
            (fsLit "y0"),           (fsLit "y0f"),          (fsLit "y0l"),
            (fsLit "y1"),           (fsLit "y1f"),          (fsLit "y1l"),
            (fsLit "yn"),           (fsLit "ynf"),          (fsLit "ynl"),

            -- These functions are described in IEEE Std 754-2008 -
            -- Standard for Floating-Point Arithmetic and ISO/IEC TS 18661
            (fsLit "nextup"),       (fsLit "nextupf"),      (fsLit "nextupl"),
            (fsLit "nextdown"),     (fsLit "nextdownf"),    (fsLit "nextdownl")
        ]

    -- -----------------------------------------------------------------------------
    -- | Is a CLabel visible outside this object file or not?
    --      From the point of view of the code generator, a name is
    --      externally visible if it has to be declared as exported
    --      in the .o file's symbol table; that is, made non-static.
    externallyVisibleCLabel :: CLabel -> Bool -- not C "static"
    externallyVisibleCLabel (StringLitLabel _)      = False
    externallyVisibleCLabel (AsmTempLabel _)        = False
    externallyVisibleCLabel (AsmTempDerivedLabel _ _)= False
    externallyVisibleCLabel (RtsLabel _)            = True
    externallyVisibleCLabel (LocalBlockLabel _)     = False
    externallyVisibleCLabel (CmmLabel _ _ _ _)      = True
    externallyVisibleCLabel (ForeignLabel{})        = True
    externallyVisibleCLabel (IdLabel name _ info)   = isExternalName name && externallyVisibleIdLabel info
    externallyVisibleCLabel (CC_Label _)            = True
    externallyVisibleCLabel (CCS_Label _)           = True
    externallyVisibleCLabel (IPE_Label {})          = True
    externallyVisibleCLabel (DynamicLinkerLabel _ _)  = False
    externallyVisibleCLabel (HpcTicksLabel _)       = True
    externallyVisibleCLabel (LargeBitmapLabel _)    = False
    externallyVisibleCLabel (SRTLabel _)            = False
    externallyVisibleCLabel (PicBaseLabel {}) = panic "externallyVisibleCLabel PicBaseLabel"
    externallyVisibleCLabel (DeadStripPreventer {}) = panic "externallyVisibleCLabel DeadStripPreventer"

    externallyVisibleIdLabel :: IdLabelInfo -> Bool
    externallyVisibleIdLabel LocalInfoTable  = False
    externallyVisibleIdLabel LocalEntry      = False
    externallyVisibleIdLabel BlockInfoTable  = False
    externallyVisibleIdLabel _               = True

    -- -----------------------------------------------------------------------------
    -- Finding the "type" of a CLabel

    -- For generating correct types in label declarations:

    data CLabelType
      = CodeLabel   -- Address of some executable instructions
      | DataLabel   -- Address of data, not a GC ptr
      | GcPtrLabel  -- Address of a (presumably static) GC object

    isCFunctionLabel :: CLabel -> Bool
    isCFunctionLabel lbl = case labelType lbl of
                            CodeLabel -> True
                            _other    -> False

    isGcPtrLabel :: CLabel -> Bool
    isGcPtrLabel lbl = case labelType lbl of
                            GcPtrLabel -> True
                            _other     -> False

    -- | Work out the general type of data at the address of this label
    --    whether it be code, data, or static GC object.
    labelType :: CLabel -> CLabelType
    labelType (IdLabel _ _ info)                    = idInfoLabelType info
    labelType (CmmLabel _ _ _ CmmData)              = DataLabel
    labelType (CmmLabel _ _ _ CmmClosure)           = GcPtrLabel
    labelType (CmmLabel _ _ _ CmmCode)              = CodeLabel
    labelType (CmmLabel _ _ _ CmmInfo)              = DataLabel
    labelType (CmmLabel _ _ _ CmmEntry)             = CodeLabel
    labelType (CmmLabel _ _ _ CmmPrimCall)          = CodeLabel
    labelType (CmmLabel _ _ _ CmmRetInfo)           = DataLabel
    labelType (CmmLabel _ _ _ CmmRet)               = CodeLabel
    labelType (RtsLabel (RtsSelectorInfoTable _ _)) = DataLabel
    labelType (RtsLabel (RtsApInfoTable _ _))       = DataLabel
    labelType (RtsLabel (RtsApFast _))              = CodeLabel
    labelType (RtsLabel _)                          = DataLabel
    labelType (LocalBlockLabel _)                   = CodeLabel
    labelType (SRTLabel _)                          = DataLabel
    labelType (ForeignLabel _ _ _ IsFunction)       = CodeLabel
    labelType (ForeignLabel _ _ _ IsData)           = DataLabel
    labelType (AsmTempLabel _)                      = panic "labelType(AsmTempLabel)"
    labelType (AsmTempDerivedLabel _ _)             = panic "labelType(AsmTempDerivedLabel)"
    labelType (StringLitLabel _)                    = DataLabel
    labelType (CC_Label _)                          = DataLabel
    labelType (CCS_Label _)                         = DataLabel
    labelType (IPE_Label {})                        = DataLabel
    labelType (DynamicLinkerLabel _ _)              = DataLabel -- Is this right?
    labelType PicBaseLabel                          = DataLabel
    labelType (DeadStripPreventer _)                = DataLabel
    labelType (HpcTicksLabel _)                     = DataLabel
    labelType (LargeBitmapLabel _)                  = DataLabel

    idInfoLabelType :: IdLabelInfo -> CLabelType
    idInfoLabelType info =
      case info of
        InfoTable     -> DataLabel
        LocalInfoTable -> DataLabel
        BlockInfoTable -> DataLabel
        Closure       -> GcPtrLabel
        ConInfoTable {} -> DataLabel
        ClosureTable  -> DataLabel
        RednCounts    -> DataLabel
        Bytes         -> DataLabel
        _             -> CodeLabel

    -- -----------------------------------------------------------------------------

    -- | Is a 'CLabel' defined in the current module being compiled?
    --
    -- Sometimes we can optimise references within a compilation unit in ways that
    -- we couldn't for inter-module references. This provides a conservative
    -- estimate of whether a 'CLabel' lives in the current module.
    isLocalCLabel :: Module -> CLabel -> Bool
    isLocalCLabel this_mod lbl =
      case lbl of
        IdLabel name _ _
          | isInternalName name -> True
          | otherwise           -> nameModule name == this_mod
        LocalBlockLabel _       -> True
        _                       -> False

    -- -----------------------------------------------------------------------------

    -- | Does a 'CLabel' need dynamic linkage?
    --
    -- When referring to data in code, we need to know whether
    -- that data resides in a DLL or not. [Win32 only.]
    -- @labelDynamic@ returns @True@ if the label is located
    -- in a DLL, be it a data reference or not.
    labelDynamic :: NCGConfig -> CLabel -> Bool
    labelDynamic config lbl =
      case lbl of
       -- is the RTS in a DLL or not?
       RtsLabel _ ->
         externalDynamicRefs && (this_unit /= rtsUnitId)

       IdLabel n _ _ ->
         externalDynamicRefs && isDynLinkName platform this_mod n

       -- When compiling in the "dyn" way, each package is to be linked into
       -- its own shared library.
       CmmLabel lbl_unit _ _ _
        | os == OSMinGW32 -> externalDynamicRefs && (this_unit /= lbl_unit)
        | otherwise       -> externalDynamicRefs

       LocalBlockLabel _    -> False

       ForeignLabel _ _ source _  ->
           if os == OSMinGW32
           then case source of
                -- Foreign label is in some un-named foreign package (or DLL).
                ForeignLabelInExternalPackage -> True

                -- Foreign label is linked into the same package as the
                -- source file currently being compiled.
                ForeignLabelInThisPackage -> False

                -- Foreign label is in some named package.
                -- When compiling in the "dyn" way, each package is to be
                -- linked into its own DLL.
                ForeignLabelInPackage pkgId ->
                    externalDynamicRefs && (this_unit /= pkgId)

           else -- On Mac OS X and on ELF platforms, false positives are OK,
                -- so we claim that all foreign imports come from dynamic
                -- libraries
                True

       CC_Label cc ->
         externalDynamicRefs && not (ccFromThisModule cc this_mod)

       -- CCS_Label always contains a CostCentre defined in the current module
       CCS_Label _ -> False
       IPE_Label {} -> True

       HpcTicksLabel m ->
         externalDynamicRefs && this_mod /= m

       -- Note that DynamicLinkerLabels do NOT require dynamic linking themselves.
       _                 -> False
      where
        externalDynamicRefs = ncgExternalDynamicRefs config
        platform = ncgPlatform config
        os = platformOS platform
        this_mod = ncgThisModule config
        this_unit = toUnitId (moduleUnit this_mod)

    -----------------------------------------------------------------------------
    -- Printing out CLabels.

    {-
    Convention:

          <name>_<type>

    where <name> is <Module>_<name> for external names and <unique> for
    internal names. <type> is one of the following:

             info                   Info table
             srt                    Static reference table
             entry                  Entry code (function, closure)
             slow                   Slow entry code (if any)
             ret                    Direct return address
             vtbl                   Vector table
             <n>_alt                Case alternative (tag n)
             dflt                   Default case alternative
             btm                    Large bitmap vector
             closure                Static closure
             con_entry              Dynamic Constructor entry code
             con_info               Dynamic Constructor info table
             static_entry           Static Constructor entry code
             static_info            Static Constructor info table
             sel_info               Selector info table
             sel_entry              Selector entry code
             cc                     Cost centre
             ccs                    Cost centre stack

    Many of these distinctions are only for documentation reasons.  For
    example, _ret is only distinguished from _entry to make it easy to
    tell whether a code fragment is a return point or a closure/function
    entry.

    Note [Closure and info labels]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    For a function 'foo, we have:
       foo_info    : Points to the info table describing foo's closure
                     (and entry code for foo with tables next to code)
       foo_closure : Static (no-free-var) closure only:
                     points to the statically-allocated closure

    For a data constructor (such as Just or Nothing), we have:
        Just_con_info: Info table for the data constructor itself
                       the first word of a heap-allocated Just
        Just_info:     Info table for the *worker function*, an
                       ordinary Haskell function of arity 1 that
                       allocates a (Just x) box:
                          Just = \x -> Just x
        Just_closure:  The closure for this worker

        Nothing_closure: a statically allocated closure for Nothing
        Nothing_static_info: info table for Nothing_closure

    All these must be exported symbol, EXCEPT Just_info.  We don't need to
    export this because in other modules we either have
           * A reference to 'Just'; use Just_closure
           * A saturated call 'Just x'; allocate using Just_con_info
    Not exporting these Just_info labels reduces the number of symbols
    somewhat.

    Note [Bytes label]
    ~~~~~~~~~~~~~~~~~~
    For a top-level string literal 'foo', we have just one symbol 'foo_bytes', which
    points to a static data block containing the content of the literal.

    Note [Proc-point local block entry-points]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    A label for a proc-point local block entry-point has no "_entry" suffix. With
    `infoTblLbl` we derive an info table label from a proc-point block ID. If
    we convert such an info table label into an entry label we must produce
    the label without an "_entry" suffix. So an info table label records
    the fact that it was derived from a block ID in `IdLabelInfo` as
    `BlockInfoTable`.

    The info table label and the local block label are both local labels
    and are not externally visible.
    -}

    instance OutputableP Platform CLabel where
      pdoc platform lbl = getPprStyle $ \case
                            PprCode CStyle   -> pprCLabel platform CStyle lbl
                            PprCode AsmStyle -> pprCLabel platform AsmStyle lbl
                            _                -> pprCLabel platform CStyle lbl
                                                -- default to CStyle

    pprCLabel :: Platform -> LabelStyle -> CLabel -> SDoc
    pprCLabel platform sty lbl =
      let
        -- some platform (e.g. Darwin) require a leading "_" for exported asm
        -- symbols
        maybe_underscore :: SDoc -> SDoc
        maybe_underscore doc = case sty of
          AsmStyle | platformLeadingUnderscore platform -> pp_cSEP <> doc
          _                                             -> doc

        tempLabelPrefixOrUnderscore :: Platform -> SDoc
        tempLabelPrefixOrUnderscore platform = case sty of
          AsmStyle -> ptext (asmTempLabelPrefix platform)
          CStyle   -> char '_'

      in case lbl of
       LocalBlockLabel u -> case sty of
          AsmStyle -> tempLabelPrefixOrUnderscore platform <> pprUniqueAlways u
          CStyle   -> tempLabelPrefixOrUnderscore platform <> text "blk_" <> pprUniqueAlways u

       AsmTempLabel u
          -> tempLabelPrefixOrUnderscore platform <> pprUniqueAlways u

       AsmTempDerivedLabel l suf
          -> ptext (asmTempLabelPrefix platform)
             <> case l of AsmTempLabel u    -> pprUniqueAlways u
                          LocalBlockLabel u -> pprUniqueAlways u
                          _other            -> pprCLabel platform sty l
             <> ftext suf

       DynamicLinkerLabel info lbl
          -> pprDynamicLinkerAsmLabel platform info (pprCLabel platform AsmStyle lbl)

       PicBaseLabel
          -> text "1b"

       DeadStripPreventer lbl
          ->
          {-
             `lbl` can be temp one but we need to ensure that dsp label will stay
             in the final binary so we prepend non-temp prefix ("dsp_") and
             optional `_` (underscore) because this is how you mark non-temp symbols
             on some platforms (Darwin)
          -}
          maybe_underscore $ text "dsp_" <> pprCLabel platform sty lbl <> text "_dsp"

       StringLitLabel u
          -> maybe_underscore $ pprUniqueAlways u <> ptext (sLit "_str")

       ForeignLabel fs (Just sz) _ _
          | AsmStyle <- sty
          , OSMinGW32 <- platformOS platform
          -> -- In asm mode, we need to put the suffix on a stdcall ForeignLabel.
             -- (The C compiler does this itself).
             maybe_underscore $ ftext fs <> char '@' <> int sz

       ForeignLabel fs _ _ _
          -> maybe_underscore $ ftext fs

       IdLabel name _cafs flavor -> case sty of
          AsmStyle -> maybe_underscore $ internalNamePrefix <> ppr name <> ppIdFlavor flavor
                       where
                          isRandomGenerated = not (isExternalName name)
                          internalNamePrefix =
                             if isRandomGenerated
                                then ptext (asmTempLabelPrefix platform)
                                else empty
          CStyle   -> ppr name <> ppIdFlavor flavor

       SRTLabel u
          -> maybe_underscore $ tempLabelPrefixOrUnderscore platform <> pprUniqueAlways u <> pp_cSEP <> text "srt"

       RtsLabel (RtsApFast (NonDetFastString str))
          -> maybe_underscore $ ftext str <> text "_fast"

       RtsLabel (RtsSelectorInfoTable upd_reqd offset)
          -> maybe_underscore $ hcat [text "stg_sel_", text (show offset),
                                      ptext (if upd_reqd
                                             then (sLit "_upd_info")
                                             else (sLit "_noupd_info"))
                                     ]

       RtsLabel (RtsSelectorEntry upd_reqd offset)
          -> maybe_underscore $ hcat [text "stg_sel_", text (show offset),
                                            ptext (if upd_reqd
                                                    then (sLit "_upd_entry")
                                                    else (sLit "_noupd_entry"))
                                     ]

       RtsLabel (RtsApInfoTable upd_reqd arity)
          -> maybe_underscore $ hcat [text "stg_ap_", text (show arity),
                                            ptext (if upd_reqd
                                                    then (sLit "_upd_info")
                                                    else (sLit "_noupd_info"))
                                     ]

       RtsLabel (RtsApEntry upd_reqd arity)
          -> maybe_underscore $ hcat [text "stg_ap_", text (show arity),
                                            ptext (if upd_reqd
                                                    then (sLit "_upd_entry")
                                                    else (sLit "_noupd_entry"))
                                     ]

       RtsLabel (RtsPrimOp primop)
          -> maybe_underscore $ text "stg_" <> ppr primop

       RtsLabel (RtsSlowFastTickyCtr pat)
          -> maybe_underscore $ text "SLOW_CALL_fast_" <> text pat <> ptext (sLit "_ctr")

       LargeBitmapLabel u
          -> maybe_underscore $ tempLabelPrefixOrUnderscore platform
                                <> char 'b' <> pprUniqueAlways u <> pp_cSEP <> text "btm"
                                -- Some bitmaps for tuple constructors have a numeric tag (e.g. '7')
                                -- until that gets resolved we'll just force them to start
                                -- with a letter so the label will be legal assembly code.

       HpcTicksLabel mod
          -> maybe_underscore $ text "_hpc_tickboxes_"  <> ppr mod <> ptext (sLit "_hpc")

       CC_Label cc   -> maybe_underscore $ ppr cc
       CCS_Label ccs -> maybe_underscore $ ppr ccs
       IPE_Label (InfoProvEnt l _ _ m _) -> maybe_underscore $ (pprCode CStyle (pdoc platform l) <> text "_" <> ppr m <> text "_ipe")

       CmmLabel _ _ fs CmmCode     -> maybe_underscore $ ftext fs
       CmmLabel _ _ fs CmmData     -> maybe_underscore $ ftext fs
       CmmLabel _ _ fs CmmPrimCall -> maybe_underscore $ ftext fs
       CmmLabel _ _ fs CmmInfo     -> maybe_underscore $ ftext fs <> text "_info"
       CmmLabel _ _ fs CmmEntry    -> maybe_underscore $ ftext fs <> text "_entry"
       CmmLabel _ _ fs CmmRetInfo  -> maybe_underscore $ ftext fs <> text "_info"
       CmmLabel _ _ fs CmmRet      -> maybe_underscore $ ftext fs <> text "_ret"
       CmmLabel _ _ fs CmmClosure  -> maybe_underscore $ ftext fs <> text "_closure"

    -- Note [Internal proc labels]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    --
    -- Some tools (e.g. the `perf` utility on Linux) rely on the symbol table
    -- for resolution of function names. To help these tools we provide the
    -- (enabled by default) -fexpose-all-symbols flag which causes GHC to produce
    -- symbols even for symbols with are internal to a module (although such
    -- symbols will have only local linkage).
    --
    -- Note that these labels are *not* referred to by code. They are strictly for
    -- diagnostics purposes.
    --
    -- To avoid confusion, it is desirable to add a module-qualifier to the
    -- symbol name. However, the Name type's Internal constructor doesn't carry
    -- knowledge of the current Module. Consequently, we have to pass this around
    -- explicitly.

    -- | Generate a label for a procedure internal to a module (if
    -- 'Opt_ExposeAllSymbols' is enabled).
    -- See Note [Internal proc labels].
    ppInternalProcLabel :: Module     -- ^ the current module
                        -> CLabel
                        -> Maybe SDoc -- ^ the internal proc label
    ppInternalProcLabel this_mod (IdLabel nm _ flavour)
      | isInternalName nm
      = Just
         $ text "_" <> ppr this_mod
        <> char '_'
        <> ztext (zEncodeFS (occNameFS (occName nm)))
        <> char '_'
        <> pprUniqueAlways (getUnique nm)
        <> ppIdFlavor flavour
    ppInternalProcLabel _ _ = Nothing

    ppIdFlavor :: IdLabelInfo -> SDoc
    ppIdFlavor x = pp_cSEP <> case x of
       Closure          -> text "closure"
       InfoTable        -> text "info"
       LocalInfoTable   -> text "info"
       Entry            -> text "entry"
       LocalEntry       -> text "entry"
       Slow             -> text "slow"
       RednCounts       -> text "ct"
       ConEntry loc      ->
          case loc of
            DefinitionSite -> text "con_entry"
            UsageSite m n ->
              ppr m <> pp_cSEP <> ppr n <> pp_cSEP <> text "con_entry"
       ConInfoTable k   ->
        case k of
          DefinitionSite -> text "con_info"
          UsageSite m n ->
            ppr m <> pp_cSEP <> ppr n <> pp_cSEP <> text "con_info"
       ClosureTable     -> text "closure_tbl"
       Bytes            -> text "bytes"
       BlockInfoTable   -> text "info"

    pp_cSEP :: SDoc
    pp_cSEP = char '_'

    instance Outputable ForeignLabelSource where
     ppr fs
      = case fs of
            ForeignLabelInPackage pkgId     -> parens $ text "package: " <> ppr pkgId
            ForeignLabelInThisPackage       -> parens $ text "this package"
            ForeignLabelInExternalPackage   -> parens $ text "external package"

    -- -----------------------------------------------------------------------------
    -- Machine-dependent knowledge about labels.

    asmTempLabelPrefix :: Platform -> PtrString  -- for formatting labels
    asmTempLabelPrefix platform = case platformOS platform of
        OSDarwin -> sLit "L"
        OSAIX    -> sLit "__L" -- follow IBM XL C's convention
        _        -> sLit ".L"

    pprDynamicLinkerAsmLabel :: Platform -> DynamicLinkerLabelInfo -> SDoc -> SDoc
    pprDynamicLinkerAsmLabel platform dllInfo ppLbl =
        case platformOS platform of
          OSDarwin
            | platformArch platform == ArchX86_64 ->
              case dllInfo of
                CodeStub        -> char 'L' <> ppLbl <> text "$stub"
                SymbolPtr       -> char 'L' <> ppLbl <> text "$non_lazy_ptr"
                GotSymbolPtr    -> ppLbl <> text "@GOTPCREL"
                GotSymbolOffset -> ppLbl
            | otherwise ->
              case dllInfo of
                CodeStub  -> char 'L' <> ppLbl <> text "$stub"
                SymbolPtr -> char 'L' <> ppLbl <> text "$non_lazy_ptr"
                _         -> panic "pprDynamicLinkerAsmLabel"

          OSAIX ->
              case dllInfo of
                SymbolPtr -> text "LC.." <> ppLbl -- GCC's naming convention
                _         -> panic "pprDynamicLinkerAsmLabel"

          _ | osElfTarget (platformOS platform) -> elfLabel

          OSMinGW32 ->
              case dllInfo of
                SymbolPtr -> text "__imp_" <> ppLbl
                _         -> panic "pprDynamicLinkerAsmLabel"

          _ -> panic "pprDynamicLinkerAsmLabel"
      where
        elfLabel
          | platformArch platform == ArchPPC
          = case dllInfo of
              CodeStub  -> -- See Note [.LCTOC1 in PPC PIC code]
                           ppLbl <> text "+32768@plt"
              SymbolPtr -> text ".LC_" <> ppLbl
              _         -> panic "pprDynamicLinkerAsmLabel"

          | platformArch platform == ArchX86_64
          = case dllInfo of
              CodeStub        -> ppLbl <> text "@plt"
              GotSymbolPtr    -> ppLbl <> text "@gotpcrel"
              GotSymbolOffset -> ppLbl
              SymbolPtr       -> text ".LC_" <> ppLbl

          | platformArch platform == ArchPPC_64 ELF_V1
            || platformArch platform == ArchPPC_64 ELF_V2
          = case dllInfo of
              GotSymbolPtr    -> text ".LC_"  <> ppLbl <> text "@toc"
              GotSymbolOffset -> ppLbl
              SymbolPtr       -> text ".LC_" <> ppLbl
              _               -> panic "pprDynamicLinkerAsmLabel"

          | otherwise
          = case dllInfo of
              CodeStub        -> ppLbl <> text "@plt"
              SymbolPtr       -> text ".LC_" <> ppLbl
              GotSymbolPtr    -> ppLbl <> text "@got"
              GotSymbolOffset -> ppLbl <> text "@gotoff"

    -- Figure out whether `symbol` may serve as an alias
    -- to `target` within one compilation unit.
    --
    -- This is true if any of these holds:
    -- * `target` is a module-internal haskell name.
    -- * `target` is an exported name, but comes from the same
    --   module as `symbol`
    --
    -- These are sufficient conditions for establishing e.g. a
    -- GNU assembly alias ('.equiv' directive). Sadly, there is
    -- no such thing as an alias to an imported symbol (conf.
    -- http://blog.omega-prime.co.uk/2011/07/06/the-sad-state-of-symbol-aliases/)
    -- See note [emit-time elimination of static indirections].
    --
    -- Precondition is that both labels represent the
    -- same semantic value.

    mayRedirectTo :: CLabel -> CLabel -> Bool
    mayRedirectTo symbol target
     | Just nam <- haskellName
     , staticClosureLabel
     , isExternalName nam
     , Just mod <- nameModule_maybe nam
     , Just anam <- hasHaskellName symbol
     , Just amod <- nameModule_maybe anam
     = amod == mod

     | Just nam <- haskellName
     , staticClosureLabel
     , isInternalName nam
     = True

     | otherwise = False
       where staticClosureLabel = isStaticClosureLabel target
             haskellName = hasHaskellName target

    {-
    Note [emit-time elimination of static indirections]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    As described in #15155, certain static values are representationally
    equivalent, e.g. 'cast'ed values (when created by 'newtype' wrappers).

                 newtype A = A Int
                 {-# NOINLINE a #-}
                 a = A 42

    a1_rYB :: Int
    [GblId, Caf=NoCafRefs, Unf=OtherCon []]
    a1_rYB = GHC.Types.I# 42#

    a [InlPrag=NOINLINE] :: A
    [GblId, Unf=OtherCon []]
    a = a1_rYB `cast` (Sym (T15155.N:A[0]) :: Int ~R# A)

    Formerly we created static indirections for these (IND_STATIC), which
    consist of a statically allocated forwarding closure that contains
    the (possibly tagged) indirectee. (See CMM/assembly below.)
    This approach is suboptimal for two reasons:
      (a) they occupy extra space,
      (b) they need to be entered in order to obtain the indirectee,
          thus they cannot be tagged.

    Fortunately there is a common case where static indirections can be
    eliminated while emitting assembly (native or LLVM), viz. when the
    indirectee is in the same module (object file) as the symbol that
    points to it. In this case an assembly-level identification can
    be created ('.equiv' directive), and as such the same object will
    be assigned two names in the symbol table. Any of the identified
    symbols can be referenced by a tagged pointer.

    Currently the 'mayRedirectTo' predicate will
    give a clue whether a label can be equated with another, already
    emitted, label (which can in turn be an alias). The general mechanics
    is that we identify data (IND_STATIC closures) that are amenable
    to aliasing while pretty-printing of assembly output, and emit the
    '.equiv' directive instead of static data in such a case.

    Here is a sketch how the output is massaged:

                         Consider
    newtype A = A Int
    {-# NOINLINE a #-}
    a = A 42                                -- I# 42# is the indirectee
                                            -- 'a' is exported

                     results in STG

    a1_rXq :: GHC.Types.Int
    [GblId, Caf=NoCafRefs, Unf=OtherCon []] =
        CCS_DONT_CARE GHC.Types.I#! [42#];

    T15155.a [InlPrag=NOINLINE] :: T15155.A
    [GblId, Unf=OtherCon []] =
        CAF_ccs  \ u  []  a1_rXq;

                     and CMM

    [section ""data" . a1_rXq_closure" {
         a1_rXq_closure:
             const GHC.Types.I#_con_info;
             const 42;
     }]

    [section ""data" . T15155.a_closure" {
         T15155.a_closure:
             const stg_IND_STATIC_info;
             const a1_rXq_closure+1;
             const 0;
             const 0;
     }]

    The emitted assembly is

    ==== INDIRECTEE
    a1_rXq_closure:                         -- module local haskell value
            .quad   GHC.Types.I#_con_info   -- an Int
            .quad   42

    ==== BEFORE
    .globl T15155.a_closure                 -- exported newtype wrapped value
    T15155.a_closure:
            .quad   stg_IND_STATIC_info     -- the closure info
            .quad   a1_rXq_closure+1        -- indirectee ('+1' being the tag)
            .quad   0
            .quad   0

    ==== AFTER
    .globl T15155.a_closure                 -- exported newtype wrapped value
    .equiv a1_rXq_closure,T15155.a_closure  -- both are shared

    The transformation is performed because
         T15155.a_closure `mayRedirectTo` a1_rXq_closure+1
    returns True.
    -}