diff options
Diffstat (limited to 'compiler/GHC/Stg/Unarise.hs')
| -rw-r--r-- | compiler/GHC/Stg/Unarise.hs | 24 |
1 files changed, 23 insertions, 1 deletions
diff --git a/compiler/GHC/Stg/Unarise.hs b/compiler/GHC/Stg/Unarise.hs index d46719298e..23c2646f73 100644 --- a/compiler/GHC/Stg/Unarise.hs +++ b/compiler/GHC/Stg/Unarise.hs @@ -186,6 +186,18 @@ So we pass type arguments of the DataCon's TyCon in StgConApp to decide what layout to use. Note that unlifted values can't be let-bound, so we don't need types in StgRhsCon. +Note [UnariseEnv] +~~~~~~~~~~~~~~~~~~ +At any variable occurrence 'v', +* If the UnariseEnv has a binding for 'v', the binding says what 'v' is bound to +* If not, 'v' stands just for itself. + +Most variables are unaffected by unarisation, and (for efficiency) we don't put +them in the UnariseEnv at all. But NB: when we go under a binding for 'v' we must +remember to delete 'v' from the UnariseEnv, lest occurrences of 'v' see the outer +binding for the variable (#21396). + + Note [UnariseEnv can map to literals] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ To avoid redundant case expressions when unarising unboxed sums, UnariseEnv @@ -305,6 +317,8 @@ instance Outputable UnariseVal where ppr (UnaryVal arg) = text "UnaryVal" <+> ppr arg -- | Extend the environment, checking the UnariseEnv invariant. +-- The id is mapped to one or more things. +-- See Note [UnariseEnv] extendRho :: UnariseEnv -> Id -> UnariseVal -> UnariseEnv extendRho rho x (MultiVal args) = assert (all (isNvUnaryType . stgArgType) args) @@ -312,6 +326,14 @@ extendRho rho x (MultiVal args) extendRho rho x (UnaryVal val) = assert (isNvUnaryType (stgArgType val)) extendVarEnv rho x (UnaryVal val) +-- Properly shadow things from an outer scope. +-- See Note [UnariseEnv] + +-- The id stands for itself so we don't record a mapping. +-- See Note [UnariseEnv] +extendRhoWithoutValue :: UnariseEnv -> Id -> UnariseEnv +extendRhoWithoutValue rho x = delVarEnv rho x + -------------------------------------------------------------------------------- @@ -754,7 +776,7 @@ unariseArgBinder is_con_arg rho x = -> do x' <- mkId (mkFastString "us") (primRepToType rep) return (extendRho rho x (MultiVal [StgVarArg x']), [x']) | otherwise - -> return (rho, [x]) + -> return (extendRhoWithoutValue rho x, [x]) reps -> do xs <- mkIds (mkFastString "us") (map primRepToType reps) |