diff options
Diffstat (limited to 'libraries/base/Unsafe/Coerce.hs')
| -rw-r--r-- | libraries/base/Unsafe/Coerce.hs | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/libraries/base/Unsafe/Coerce.hs b/libraries/base/Unsafe/Coerce.hs index cc230facbe..cfb4eac439 100644 --- a/libraries/base/Unsafe/Coerce.hs +++ b/libraries/base/Unsafe/Coerce.hs @@ -22,7 +22,6 @@ import GHC.Natural () -- See Note [Depend on GHC.Natural] in GHC.Base import GHC.Types {- Note [Implementing unsafeCoerce] - ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The implementation of unsafeCoerce is surprisingly subtle. This Note describes the moving parts. You will find more @@ -126,9 +125,13 @@ several ways Flaoting the case is OK here, even though it broardens the scope, becuase we are done with simplification. -(U4) GHC.CoreToStg.Prep.cpeExprIsTrivial anticipated the +(U4) GHC.CoreToStg.Prep.cpeExprIsTrivial anticipates the upcoming discard of unsafeEqualityProof. +(U4a) Ditto GHC.Core.Unfold.inlineBoringOk we want to treat + the RHS of unsafeCoerce as very small; see + Note [Inline unsafeCoerce] in that module. + (U5) The definition of unsafeEqualityProof in Unsafe.Coerce looks very strange: unsafeEqualityProof = case unsafeEqualityProof @a @b of @@ -161,7 +164,7 @@ several ways to simplify the ase when the two tpyes are equal. (U8) The is a super-magic RULE in GHC.base - map cocerce = coerce + map coerce = coerce (see Note [Getting the map/coerce RULE to work] in CoreOpt) But it's all about turning coerce into a cast, and unsafeCoerce no longer does that. So we need a separate map/unsafeCoerce |