[commit: ghc] ghc-8.0: Do not init record accessors as exported (9d9eaec)

[git at git.haskell.org]

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

On branch  : ghc-8.0
Link       : http://ghc.haskell.org/trac/ghc/changeset/9d9eaeca03e138e0b35351c9401c832996398641/ghc

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

commit 9d9eaeca03e138e0b35351c9401c832996398641
Author: Ömer Sinan Ağacan <omeragacan at gmail.com>
Date:   Fri May 27 11:02:47 2016 -0400

    Do not init record accessors as exported
    
    This was causing redundant code generation when accessors are not
    actually exported, as they were being marked as "exported" at
    initialization.
    
    Test Plan: validate
    
    Reviewers: simonpj, austin, bgamari
    
    Reviewed By: simonpj
    
    Subscribers: mpickering, thomie
    
    Differential Revision: https://phabricator.haskell.org/D2270
    
    (cherry picked from commit 3a00ff92a3ee66c096b85b180d247d1a471a6b6e)


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

9d9eaeca03e138e0b35351c9401c832996398641
 compiler/basicTypes/Id.hs       | 7 +++++++
 compiler/deSugar/Desugar.hs     | 5 ++++-
 compiler/typecheck/TcTyDecls.hs | 7 ++++++-
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/compiler/basicTypes/Id.hs b/compiler/basicTypes/Id.hs
index e55259b..990a192 100644
--- a/compiler/basicTypes/Id.hs
+++ b/compiler/basicTypes/Id.hs
@@ -33,6 +33,7 @@ module Id (
         mkLocalId, mkLocalCoVar, mkLocalIdOrCoVar,
         mkLocalIdOrCoVarWithInfo,
         mkLocalIdWithInfo, mkExportedLocalId, mkExportedVanillaId,
+        mkNonExportedLocalId,
         mkSysLocal, mkSysLocalM, mkSysLocalOrCoVar, mkSysLocalOrCoVarM,
         mkUserLocal, mkUserLocalOrCoVar,
         mkTemplateLocals, mkTemplateLocalsNum, mkTemplateLocal,
@@ -287,6 +288,12 @@ mkExportedLocalId :: IdDetails -> Name -> Type -> Id
 mkExportedLocalId details name ty = Var.mkExportedLocalVar details name ty vanillaIdInfo
         -- Note [Free type variables]
 
+-- | Create a local 'Id' that is marked as not-exported.
+-- These may be removed as dead code.
+mkNonExportedLocalId :: IdDetails -> Name -> Type -> Id
+mkNonExportedLocalId details name ty =
+  Var.mkLocalVar details name ty vanillaIdInfo
+
 mkExportedVanillaId :: Name -> Type -> Id
 mkExportedVanillaId name ty = Var.mkExportedLocalVar VanillaId name ty vanillaIdInfo
         -- Note [Free type variables]
diff --git a/compiler/deSugar/Desugar.hs b/compiler/deSugar/Desugar.hs
index db4c867..365e7c9 100644
--- a/compiler/deSugar/Desugar.hs
+++ b/compiler/deSugar/Desugar.hs
@@ -295,7 +295,10 @@ deSugar hsc_env
                      (text "Desugar"<+>brackets (ppr mod))
                      (const ()) $
      do { -- Desugar the program
-        ; let export_set = availsToNameSet exports
+        ; let export_set =
+                -- Used to be 'availsToNameSet', but we now export selectors
+                -- only when necessary. See #12125.
+                availsToNameSetWithSelectors exports
               target     = hscTarget dflags
               hpcInfo    = emptyHpcInfo other_hpc_info
 
diff --git a/compiler/typecheck/TcTyDecls.hs b/compiler/typecheck/TcTyDecls.hs
index 233857c..4623744 100644
--- a/compiler/typecheck/TcTyDecls.hs
+++ b/compiler/typecheck/TcTyDecls.hs
@@ -949,7 +949,12 @@ mkOneRecordSelector all_cons idDetails fl
     lbl      = flLabel fl
     sel_name = flSelector fl
 
-    sel_id = mkExportedLocalId rec_details sel_name sel_ty
+    sel_id =
+      -- Do not mark record selectors as exported to avoid keeping these Ids
+      -- alive unnecessarily. See #12125. Selectors are now marked as exported
+      -- when necessary by desugarer ('Desugar.addExportFlagsAndRules', also see
+      -- uses of 'availsToNameSetWithSelectors' in 'Desugar.hs').
+      mkNonExportedLocalId rec_details sel_name sel_ty
     rec_details = RecSelId { sel_tycon = idDetails, sel_naughty = is_naughty }
 
     -- Find a representative constructor, con1