diff options
Diffstat (limited to 'utils')
| -rw-r--r-- | utils/genprimopcode/Main.hs | 37 |
1 files changed, 30 insertions, 7 deletions
diff --git a/utils/genprimopcode/Main.hs b/utils/genprimopcode/Main.hs index bf1ed76f9e..6984f4a296 100644 --- a/utils/genprimopcode/Main.hs +++ b/utils/genprimopcode/Main.hs @@ -417,18 +417,41 @@ asInfix :: String -> String asInfix nm | isAlpha (head nm) = "`" ++ nm ++ "`" | otherwise = nm + +{- Note [OPTIONS_GHC in GHC.PrimopWrappers] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +In PrimopWrappers we set some crucial GHC options + +* Eta reduction: -fno-do-eta-reduction + In PrimopWrappers we builds a wrapper for each primop, thus + plusInt# = \a b. plusInt# a b + That's a pretty odd definition, becaues it looks recursive. What + actually happens is that it makes a curried, top-level bindings for + `plusInt#`. When we compile PrimopWrappers, the code generator spots + (plusInt# a b) and generates an add instruction. + + Its very important that we don't eta-reduce this to + plusInt# = plusInt# + because then the special rule in the code generator doesn't fire. + +* Worker-wrapper: performing WW on this module is harmful even, two reasons: + 1. Inferred strictness signatures are all bottom (because of the apparent + recursion), which is a lie + 2. Doing the worker/wrapper split based on that information will + introduce references to absentError, which isn't available at + this point. + + We prevent strictness analyis and w/w by simply doing -O0. It's + a very simple module and there is no optimisation to be done +-} + gen_wrappers :: Info -> String gen_wrappers (Info _ entries) = "{-# LANGUAGE MagicHash, NoImplicitPrelude, UnboxedTuples #-}\n" -- Dependencies on Prelude must be explicit in libraries/base, but we -- don't need the Prelude here so we add NoImplicitPrelude. - ++ "{-# OPTIONS_GHC -Wno-deprecations -O0 #-}\n" - -- No point in optimising this at all. - -- Performing WW on this module is harmful even, two reasons: - -- 1. Inferred strictness signatures are all bottom, which is a lie - -- 2. Doing the worker/wrapper split based on that information will - -- introduce references to absentError, - -- which isn't available at this point. + ++ "{-# OPTIONS_GHC -Wno-deprecations -O0 -fno-do-eta-reduction #-}\n" + -- Very important OPTIONS_GHC! See Note [OPTIONS_GHC in GHC.PrimopWrappers] ++ "module GHC.PrimopWrappers where\n" ++ "import qualified GHC.Prim\n" ++ "import GHC.Tuple ()\n" |