diff options
Diffstat (limited to 'compiler/coreSyn/CoreUtils.lhs')
| -rw-r--r-- | compiler/coreSyn/CoreUtils.lhs | 29 |
1 files changed, 18 insertions, 11 deletions
diff --git a/compiler/coreSyn/CoreUtils.lhs b/compiler/coreSyn/CoreUtils.lhs index 3bf07febf3..baf7e4fa80 100644 --- a/compiler/coreSyn/CoreUtils.lhs +++ b/compiler/coreSyn/CoreUtils.lhs @@ -908,13 +908,22 @@ it's applied only to dictionaries. -- Note [exprOkForSpeculation: case expressions] below -- -- Precisely, it returns @True@ iff: +-- a) The expression guarantees to terminate, +-- b) soon, +-- c) without causing a write side effect (e.g. writing a mutable variable) +-- d) without throwing a Haskell exception +-- e) without risking an unchecked runtime exception (array out of bounds, +-- divide by zero) -- --- * The expression guarantees to terminate, --- * soon, --- * without raising an exception, --- * without causing a side effect (e.g. writing a mutable variable) +-- For @exprOkForSideEffects@ the list is the same, but omitting (e). +-- +-- Note that +-- exprIsHNF implies exprOkForSpeculation +-- exprOkForSpeculation implies exprOkForSideEffects +-- +-- See Note [PrimOp can_fail and has_side_effects] in PrimOp +-- and Note [Implementation: how can_fail/has_side_effects affect transformations] -- --- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@. -- As an example of the considerations in this test, consider: -- -- > let x = case y# +# 1# of { r# -> I# r# } @@ -964,7 +973,7 @@ app_ok :: (PrimOp -> Bool) -> Id -> [Expr b] -> Bool app_ok primop_ok fun args = case idDetails fun of DFunId _ new_type -> not new_type - -- DFuns terminate, unless the dict is implemented + -- DFuns terminate, unless the dict is implemented -- with a newtype in which case they may not DataConWorkId {} -> True @@ -983,14 +992,12 @@ app_ok primop_ok fun args -> True | otherwise - -> primop_ok op -- A bit conservative: we don't really need - && all (expr_ok primop_ok) args - - -- to care about lazy arguments, but this is easy + -> primop_ok op -- A bit conservative: we don't really need + && all (expr_ok primop_ok) args -- to care about lazy arguments, but this is easy _other -> isUnLiftedType (idType fun) -- c.f. the Var case of exprIsHNF || idArity fun > n_val_args -- Partial apps - || (n_val_args == 0 && + || (n_val_args == 0 && isEvaldUnfolding (idUnfolding fun)) -- Let-bound values where n_val_args = valArgCount args |