diff options
Diffstat (limited to 'compiler/GHC/CoreToStg')
| -rw-r--r-- | compiler/GHC/CoreToStg/Prep.hs | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/compiler/GHC/CoreToStg/Prep.hs b/compiler/GHC/CoreToStg/Prep.hs index 78ce8e16f1..c0b72cefed 100644 --- a/compiler/GHC/CoreToStg/Prep.hs +++ b/compiler/GHC/CoreToStg/Prep.hs @@ -1648,12 +1648,16 @@ long as the callee might evaluate it. And if it is evaluated on most code paths anyway, we get to turn the unknown eval in the callee into a known call at the call site. -However, we must be very careful not to speculate recursive calls! -Doing so might well change termination behavior. +Very Nasty Wrinkle + +We must be very careful not to speculate recursive calls! Doing so +might well change termination behavior. That comes up in practice for DFuns, which are considered ok-for-spec, because they always immediately return a constructor. -Not so if you speculate the recursive call, as #20836 shows: +See Note [NON-BOTTOM-DICTS invariant] in GHC.Core. + +But not so if you speculate the recursive call, as #20836 shows: class Foo m => Foo m where runFoo :: m a -> m a |