diff options
Diffstat (limited to 'libraries/base/Unsafe/Coerce.hs')
| -rw-r--r-- | libraries/base/Unsafe/Coerce.hs | 32 |
1 files changed, 9 insertions, 23 deletions
diff --git a/libraries/base/Unsafe/Coerce.hs b/libraries/base/Unsafe/Coerce.hs index 07d1f2da9f..5ebc9c637e 100644 --- a/libraries/base/Unsafe/Coerce.hs +++ b/libraries/base/Unsafe/Coerce.hs @@ -90,10 +90,10 @@ several ways (U1) unsafeEqualityProof is /never/ inlined. -(U2) In CoreToStg.coreToStg, we transform - case unsafeEqualityProof of UnsafeRefl -> blah +(U2) In CoreToStg.Prep, we transform + case unsafeEqualityProof of UnsafeRefl g -> blah ==> - blah + blah[unsafe-co/g] This eliminates the overhead of evaluating the unsafe equality proof. @@ -127,18 +127,15 @@ several ways and produce a thunk even after discarding the unsafeEqualityProof. So instead we float out the case to give case unsafeEqualityProof ... of { UnsafeRefl -> - let a = K e + let a = e x = K a - in ... - Flaoting the case is OK here, even though it broardens the + in ... } + Floating the case is OK here, even though it broadens the scope, because we are done with simplification. -(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. +(U4) 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: @@ -212,17 +209,6 @@ There are yet more wrinkles the kind-/homogeneous/ unsafeEqualityProof twice. See Note [Wiring in unsafeCoerce#] in Desugar. - -(U11) We must also be careful to discard unsafeEqualityProof in the - bytecode generator; see ByteCodeGen.bcView. Here we don't really - care about fast execution, but (annoyingly) we /do/ care about the - GHCi debugger, and GHCi itself uses unsafeCoerce. - - Moreover, in GHC.Tc.Module.tcGhciStmts we use unsafeCoerce#, rather - than the more kosher unsafeCoerce, because (with -O0) the latter - may not be inlined. - - Sigh -} -- | This type is treated magically within GHC. Any pattern match of the |