[commit: ghc] ghc-8.2: Revert "Make raiseIO# produce topRes" (d67f047)

[git at git.haskell.org]

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

On branch  : ghc-8.2
Link       : http://ghc.haskell.org/trac/ghc/changeset/d67f0471cd3584c5a548ff30c9023b599b598d3e/ghc

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

commit d67f0471cd3584c5a548ff30c9023b599b598d3e
Author: David Feuer <david.feuer at gmail.com>
Date:   Mon Apr 3 22:25:55 2017 -0400

    Revert "Make raiseIO# produce topRes"
    
    This reverts commit da4687f63ffe5a6162e3d7856aa53de048dd0f42.
    
    It's not entirely trivial to clean up the dead code this patch
    introduced. In particular, when we see
    
    ```
    case raiseIO# m s of
      s' -> e
    ```
    
    we want to know that `e` is dead. For scrutinees that are properly
    bottom (which we don't want to consider `raiseIO# m s` to be, this
    is handled by rewriting `bot` to `case bot of {}`. But if we do
    that for `raiseIO#`, we end up with
    
    ```
    case raiseIO# m s of {}
    ```
    
    which looks a lot like bottom and could confuse demand analysis.
    I think we need to wait with this change until we have a more
    complete story.
    
    Reviewers: austin, bgamari
    
    Reviewed By: bgamari
    
    Subscribers: rwbarton, thomie
    
    Differential Revision: https://phabricator.haskell.org/D3413
    
    (cherry picked from commit e83af07e3d0b65fe6f37806e86d07f3e8dc1b01e)


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

d67f0471cd3584c5a548ff30c9023b599b598d3e
 compiler/prelude/primops.txt.pp          | 10 ++++++----
 testsuite/tests/stranal/should_run/all.T |  2 +-
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/compiler/prelude/primops.txt.pp b/compiler/prelude/primops.txt.pp
index 5d0a2a4..e9c844e 100644
--- a/compiler/prelude/primops.txt.pp
+++ b/compiler/prelude/primops.txt.pp
@@ -2005,9 +2005,11 @@ primop  RaiseOp "raise#" GenPrimOp
 -- must be *precise* - we don't want the strictness analyser turning
 -- one kind of bottom into another, as it is allowed to do in pure code.
 --
--- We currently produce topRes, which is much too conservative (interfering
--- with dead code elimination, unfortunately), but nothing else we currently
--- have on tap is actually correct.
+-- But we *do* want to know that it returns bottom after
+-- being applied to two arguments, so that this function is strict in y
+--     f x y | x>0       = raiseIO blah
+--           | y>0       = return 1
+--           | otherwise = return 2
 --
 -- TODO Check that the above notes on @f@ are valid. The function successfully
 -- produces an IO exception when compiled without optimization. If we analyze
@@ -2019,7 +2021,7 @@ primop  RaiseOp "raise#" GenPrimOp
 primop  RaiseIOOp "raiseIO#" GenPrimOp
    a -> State# RealWorld -> (# State# RealWorld, b #)
    with
-   strictness  = { \ _arity -> mkClosedStrictSig [topDmd, topDmd] topRes }
+   strictness  = { \ _arity -> mkClosedStrictSig [topDmd, topDmd] exnRes }
    out_of_line = True
    has_side_effects = True
 
diff --git a/testsuite/tests/stranal/should_run/all.T b/testsuite/tests/stranal/should_run/all.T
index a07900b..0764746 100644
--- a/testsuite/tests/stranal/should_run/all.T
+++ b/testsuite/tests/stranal/should_run/all.T
@@ -14,4 +14,4 @@ test('T11076', normal, multimod_compile_and_run, ['T11076.hs', 'T11076_prim.cmm'
 test('T11555a', normal, compile_and_run, [''])
 test('T12368', exit_code(1), compile_and_run, [''])
 test('T12368a', exit_code(1), compile_and_run, [''])
-test('T13380', exit_code(1), compile_and_run, [''])
+test('T13380', [expect_broken(13380), exit_code(1)], compile_and_run, [''])