[commit: ghc] master: Reduce non-determinism in ABI hashes with RULES and instance decls (3448f98)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/3448f9827d2364b91bc60134aa38b74849b9d54e/ghc

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

commit 3448f9827d2364b91bc60134aa38b74849b9d54e
Author: Bartosz Nitka <niteria at gmail.com>
Date:   Fri Jul 17 16:50:52 2015 +0100

    Reduce non-determinism in ABI hashes with RULES and instance decls
    
    Summary:
    Before this change the `RULES` would be attached to one for the names from
    the module that appear on the left hand side. The choice depended on the
    `uniq` that was generated, which are known to be non-deterministic (a
    separate, bigger problem). Now we use `OccName`s which should be stable.
    
    Analogously for instance declarations, but they are attached to one of
    the types involved.
    
    Test Plan:
    contbuild
    it made `Data.Text.Internal.Fusion.Common` interface stable, previously
    stream fusion rule would be attached either to `streamList` or
    `unstreamList` depending on if the module was compiled after `cabal
    clean` or after `find | grep '\.o$' | xargs rm`.
    
    Reviewers: simonpj, austin, bgamari, simonmar
    
    Subscribers: puffnfresh, thomie
    
    Differential Revision: https://phabricator.haskell.org/D1073
    
    GHC Trac Issues: #4012


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

3448f9827d2364b91bc60134aa38b74849b9d54e
 compiler/specialise/Rules.hs | 12 +++++++++---
 compiler/types/InstEnv.hs    | 13 ++++++++++---
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/compiler/specialise/Rules.hs b/compiler/specialise/Rules.hs
index cb71e3a..7cf6e56 100644
--- a/compiler/specialise/Rules.hs
+++ b/compiler/specialise/Rules.hs
@@ -180,9 +180,15 @@ mkRule this_mod is_auto is_local name act fn bndrs args rhs
     lhs_names = nameSetElems (extendNameSet (exprsOrphNames args) fn)
         -- TODO: copied from ruleLhsOrphNames
 
-    orph = case filter (nameIsLocalOrFrom this_mod) lhs_names of
-                        (n : _) -> NotOrphan (nameOccName n)
-                        []      -> IsOrphan
+        -- Since rules get eventually attached to one of the free names
+        -- from the definition when compiling the ABI hash, we should make
+        -- it deterministic. This chooses the one with minimal OccName
+        -- as opposed to uniq value.
+    local_lhs_names = filter (nameIsLocalOrFrom this_mod) lhs_names
+    anchor = minimum $ map nameOccName local_lhs_names
+    orph = case local_lhs_names of
+             (_ : _) -> NotOrphan anchor
+             []      -> IsOrphan
 
 --------------
 roughTopNames :: [CoreExpr] -> [Maybe Name]
diff --git a/compiler/types/InstEnv.hs b/compiler/types/InstEnv.hs
index f810850..db8f531 100644
--- a/compiler/types/InstEnv.hs
+++ b/compiler/types/InstEnv.hs
@@ -236,10 +236,17 @@ mkLocalInstance dfun oflag tvs cls tys
     do_one (_ltvs, rtvs) = choose_one [ns | (tv,ns) <- cls_tvs `zip` arg_names
                                           , not (tv `elem` rtvs)]
 
+    -- Since instance declarations get eventually attached to one of the types
+    -- from the definition when compiling the ABI hash, we should make
+    -- it deterministic. This chooses the one with minimal OccName
+    -- as opposed to uniq value.
     choose_one :: [NameSet] -> IsOrphan
-    choose_one nss = case nameSetElems (unionNameSets nss) of
-                        []      -> IsOrphan
-                        (n : _) -> NotOrphan (nameOccName n)
+    choose_one nss = case local_names of
+                       []      -> IsOrphan
+                       (_ : _) -> NotOrphan anchor
+      where
+      local_names = nameSetElems (unionNameSets nss)
+      anchor = minimum $ map nameOccName local_names
 
 mkImportedInstance :: Name
                    -> [Maybe Name]