[commit: ghc] wip/T11770: Demand Analyzer: Do not set OneShot information (d140500)

[git at git.haskell.org]

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

On branch  : wip/T11770
Link       : http://ghc.haskell.org/trac/ghc/changeset/d14050006e3db1aa90d063884c4cd98f0fd5e859/ghc

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

commit d14050006e3db1aa90d063884c4cd98f0fd5e859
Author: Joachim Breitner <mail at joachim-breitner.de>
Date:   Wed Mar 30 10:05:28 2016 +0200

    Demand Analyzer: Do not set OneShot information
    
    as suggested in ticket:11770#comment:1. This naturally fixes
    issue #117700; performance validation pending.
    (Pushing this as a branch to get perf.haskell.org to measure it).


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

d14050006e3db1aa90d063884c4cd98f0fd5e859
 compiler/stranal/DmdAnal.hs                  | 27 +++------------------------
 testsuite/tests/stranal/should_compile/all.T |  2 +-
 2 files changed, 4 insertions(+), 25 deletions(-)

diff --git a/compiler/stranal/DmdAnal.hs b/compiler/stranal/DmdAnal.hs
index 6ef911f..aae0c74 100644
--- a/compiler/stranal/DmdAnal.hs
+++ b/compiler/stranal/DmdAnal.hs
@@ -260,17 +260,13 @@ dmdAnal' env dmd (Case scrut case_bndr ty alts)
     (res_ty, Case scrut' case_bndr' ty alts')
 
 dmdAnal' env dmd (Let (NonRec id rhs) body)
-  = (body_ty2, Let (NonRec id2 annotated_rhs) body')
+  = (body_ty2, Let (NonRec id2 rhs') body')
   where
     (sig, lazy_fv, id1, rhs') = dmdAnalRhs NotTopLevel Nothing env id rhs
     (body_ty, body')          = dmdAnal (extendAnalEnv NotTopLevel env id sig) dmd body
     (body_ty1, id2)           = annotateBndr env body_ty id1
     body_ty2                  = addLazyFVs body_ty1 lazy_fv
 
-    -- Annotate top-level lambdas at RHS basing on the aggregated demand info
-    -- See Note [Annotating lambdas at right-hand side]
-    annotated_rhs = annLamWithShotness (idDemandInfo id2) rhs'
-
         -- If the actual demand is better than the vanilla call
         -- demand, you might think that we might do better to re-analyse
         -- the RHS with the stronger demand.
@@ -317,8 +313,8 @@ annLamWithShotness d e
       | Just (c, u') <- peelUseCall u
       , Lam bndr body <- e
       = if isTyVar bndr
-        then Lam bndr                    (go u  body)
-        else Lam (setOneShotness c bndr) (go u' body)
+        then Lam bndr (go u  body)
+        else Lam bndr (go u' body)
       | otherwise
       = e
 
@@ -432,23 +428,6 @@ free variable |y|. Conversely, if the demand on |h| is unleashed right
 on the spot, we will get the desired result, namely, that |f| is
 strict in |y|.
 
-Note [Annotating lambdas at right-hand side]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Let us take a look at the following example:
-
-g f = let x = 100
-          h = \y -> f x y
-       in h 5
-
-One can see that |h| is called just once, therefore the RHS of h can
-be annotated as a one-shot lambda. This is done by the function
-annLamWithShotness *a posteriori*, i.e., basing on the aggregated
-usage demand on |h| from the body of |let|-expression, which is C1(U)
-in this case.
-
-In other words, for locally-bound lambdas we can infer
-one-shotness.
-
 
 ************************************************************************
 *                                                                      *
diff --git a/testsuite/tests/stranal/should_compile/all.T b/testsuite/tests/stranal/should_compile/all.T
index 3ac075b..dabc9fc 100644
--- a/testsuite/tests/stranal/should_compile/all.T
+++ b/testsuite/tests/stranal/should_compile/all.T
@@ -45,6 +45,6 @@ test('T9208', when(compiler_debugged(), expect_broken(9208)), compile, [''])
 # Hence the above expect_broken.  See comments in the Trac ticket
 
 test('T10694', [ grepCoreString(r'Str=') ],   compile, ['-dppr-cols=200 -ddump-simpl'])
-test('T11770', [ expect_broken(117700), checkCoreString("OneShot") ], compile, ['-ddump-simpl'])
+test('T11770', [ checkCoreString('OneShot') ], compile, ['-ddump-simpl'])