Revert "Make raiseIO# produce topRes"

This reverts commit da4687f6.

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 e83af07e)

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
 

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, [''])