[commit: ghc] ghc-8.6: Revert "Disable the SRT offset optimisation on MachO platforms" (c15d44f)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : ghc-8.6
Link       : http://ghc.haskell.org/trac/ghc/changeset/c15d44f8b3f00bfe152c2f9d3c6f60efd204fb23/ghc

>---------------------------------------------------------------

commit c15d44f8b3f00bfe152c2f9d3c6f60efd204fb23
Author: Simon Marlow <marlowsd at gmail.com>
Date:   Thu Jul 26 17:19:54 2018 -0400

    Revert "Disable the SRT offset optimisation on MachO platforms"
    
    This reverts commit bf10456edaa03dc010821cd4c3d9f49cb11d89da.


>---------------------------------------------------------------

c15d44f8b3f00bfe152c2f9d3c6f60efd204fb23
 compiler/cmm/CLabel.hs             | 22 ++--------------------
 compiler/cmm/CmmBuildInfoTables.hs | 18 ++----------------
 compiler/cmm/CmmInfo.hs            |  5 +----
 includes/rts/storage/InfoTables.h  |  3 ---
 4 files changed, 5 insertions(+), 43 deletions(-)

diff --git a/compiler/cmm/CLabel.hs b/compiler/cmm/CLabel.hs
index 1a9bc73..472bd3c 100644
--- a/compiler/cmm/CLabel.hs
+++ b/compiler/cmm/CLabel.hs
@@ -94,12 +94,10 @@ module CLabel (
 
         mkHpcTicksLabel,
 
-        -- * Predicates
         hasCAF,
         needsCDecl, maybeLocalBlockLabel, externallyVisibleCLabel,
         isMathFun,
         isCFunctionLabel, isGcPtrLabel, labelDynamic,
-        isLocalCLabel,
 
         -- * Conversions
         toClosureLbl, toSlowEntryLbl, toEntryLbl, toInfoLbl, hasHaskellName,
@@ -976,29 +974,13 @@ idInfoLabelType info =
 
 
 -- -----------------------------------------------------------------------------
+-- Does a CLabel need dynamic linkage?
 
--- | 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 :: DynFlags -> Module -> CLabel -> Bool
 labelDynamic dflags this_mod lbl =
   case lbl of
diff --git a/compiler/cmm/CmmBuildInfoTables.hs b/compiler/cmm/CmmBuildInfoTables.hs
index 3d13fc7..ecbe89d 100644
--- a/compiler/cmm/CmmBuildInfoTables.hs
+++ b/compiler/cmm/CmmBuildInfoTables.hs
@@ -16,7 +16,6 @@ import Hoopl.Label
 import Hoopl.Collections
 import Hoopl.Dataflow
 import Module
-import Platform
 import Digraph
 import CLabel
 import PprCmmDecl ()
@@ -121,7 +120,7 @@ offset to the SRT can be stored in 32 bits (all code lives within a
 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):
+On x86_64 with TABLES_NEXT_TO_CODE:
 
 - info->srt is zero if there's no SRT, otherwise:
 - info->srt is an offset from the info pointer to the SRT object
@@ -637,27 +636,14 @@ oneSRT dflags staticFuns blockids lbls isCAF cafs = do
         let newSRTMap = Map.fromList [(cafLbl, srtEntry) | cafLbl <- lbls]
         put (Map.union newSRTMap srtMap)
 
-    this_mod = thisModule topSRT
-
   case Set.toList filtered of
     [] -> do
       srtTrace "oneSRT: empty" (ppr lbls) $ return ()
       updateSRTMap Nothing
       return ([], [], [])
 
-    -- When we have only one entry there is no need to build a new SRT at all.
     [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 in this case.
-        not (labelDynamic dflags this_mod 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 $ targetPlatform dflags)
-             || isLocalCLabel this_mod lbl) -> do
+      | not (labelDynamic dflags (thisModule topSRT) lbl) -> do
         updateSRTMap (Just one)
         return ([], map (,lbl) blockids, [])
 
diff --git a/compiler/cmm/CmmInfo.hs b/compiler/cmm/CmmInfo.hs
index 43cba25..3b2eea1 100644
--- a/compiler/cmm/CmmInfo.hs
+++ b/compiler/cmm/CmmInfo.hs
@@ -271,10 +271,7 @@ mkSRTLit dflags _ Nothing    = ([], CmmInt 0 (halfWordWidth dflags))
 mkSRTLit dflags _ (Just lbl) = ([CmmLabel lbl], CmmInt 1 (halfWordWidth dflags))
 
 
--- | Is the SRT offset field inline in the info table on this platform?
---
--- See the section "Referring to an SRT from the info table" in
--- Note [SRTs] in CmmBuildInfoTables.hs
+-- | is the SRT offset field inline in the info table on this platform?
 inlineSRT :: DynFlags -> Bool
 inlineSRT dflags = platformArch (targetPlatform dflags) == ArchX86_64
   && tablesNextToCode dflags
diff --git a/includes/rts/storage/InfoTables.h b/includes/rts/storage/InfoTables.h
index db50d16..137cfe2 100644
--- a/includes/rts/storage/InfoTables.h
+++ b/includes/rts/storage/InfoTables.h
@@ -156,9 +156,6 @@ typedef union {
 #if defined(x86_64_TARGET_ARCH) && defined(TABLES_NEXT_TO_CODE)
 // On x86_64 we can fit a pointer offset in half a word, so put the SRT offset
 // in the info->srt field directly.
-//
-// See the section "Referring to an SRT from the info table" in
-// Note [SRTs] in CmmBuildInfoTables.hs
 #define USE_INLINE_SRT_FIELD
 #endif