Fix cost-centre-stacks bug (#5654)

This fixes some cases of wrong stacks being generated by the profiler.
For background and details on the fix see
`Note [Evaluating functions with profiling]` in `rts/Apply.cmm`.

This does have an impact on allocations for some programs when
profiling.  nofib results:

```
   k-nucleotide          +0.0%     +8.8%    +11.0%    +11.0%      0.0%
         puzzle          +0.0%    +12.5%     0.244     0.246      0.0%
      typecheck           0.0%     +8.7%    +16.1%    +16.2%      0.0%
------------------------------------------------------------------------
--------
            Min          -0.0%     -0.0%    -34.4%    -35.5%    -25.0%
            Max          +0.0%    +12.5%    +48.9%    +49.4%    +10.6%
 Geometric Mean          +0.0%     +0.6%     +2.0%     +1.8%     -0.3%

```

But runtimes don't seem to be affected much, and the examples I looked
at were completely legitimate.  For example, in puzzle we have this:

```
position :: ItemType -> StateType ->  BankType
position Bono = bonoPos
position Edge = edgePos
position Larry = larryPos
position Adam = adamPos
```

where the identifiers on the rhs are all record selectors.  Previously
the profiler gave a stack that looked like

```
  position
  bonoPos
  ...
```

i.e. `bonoPos` was at the same level of the call stack as `position`,
but now it looks like

```
  position
   bonoPos
   ...
```

I used the normaliser from the testsuite to diff the profiling output
from other nofib programs and they all looked better.

Test Plan:
* the broken test passes
* validate
* compiled and ran all of nofib, measured perf, diff'd several .prof
files

Reviewers: niteria, erikd, austin, scpmw, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2804

GHC Trac Issues: #5654, #10007

1 files changed, 4 insertions, 2 deletions

diff --git a/compiler/codeGen/StgCmmClosure.hs b/compiler/codeGen/StgCmmClosure.hs
index 0ce119b0bb..1943dc4830 100644
--- a/compiler/codeGen/StgCmmClosure.hs
+++ b/compiler/codeGen/StgCmmClosure.hs
@@ -565,8 +565,10 @@ getCallMethod dflags _ id _ n_args v_args _cg_loc
 
 getCallMethod dflags name id (LFReEntrant _ _ arity _ _) n_args _v_args _cg_loc
               _self_loop_info
-  | n_args == 0    = ASSERT( arity /= 0 )
-                     ReturnIt        -- No args at all
+  | n_args == 0 -- No args at all
+  && not (gopt Opt_SccProfilingOn dflags)
+     -- See Note [Evaluating functions with profiling] in rts/Apply.cmm
+  = ASSERT( arity /= 0 ) ReturnIt
   | n_args < arity = SlowCall        -- Not enough args
   | otherwise      = DirectEntry (enterIdLabel dflags name (idCafInfo id)) arity