[Git][ghc/ghc][master] Add unsafePtrEquality# restricted to UnliftedTypes
Marge Bot (@marge-bot)
gitlab at gitlab.haskell.org
Tue Nov 22 20:59:53 UTC 2022
Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC
Commits:
9d61c182 by Oleg Grenrus at 2022-11-22T15:59:34-05:00
Add unsafePtrEquality# restricted to UnliftedTypes
- - - - -
4 changed files:
- compiler/GHC/Builtin/primops.txt.pp
- libraries/base/GHC/ArrayArray.hs
- libraries/base/GHC/Exts.hs
- libraries/ghc-prim/GHC/Prim/PtrEq.hs
Changes:
=====================================
compiler/GHC/Builtin/primops.txt.pp
=====================================
@@ -3429,29 +3429,47 @@ primop ReallyUnsafePtrEqualityOp "reallyUnsafePtrEquality#" GenPrimOp
-- The primop `reallyUnsafePtrEquality#` does a direct pointer
-- equality between two (boxed) values. Several things to note:
--
--- * It is levity-polymorphic. It works for TYPE (BoxedRep Lifted) and
--- TYPE (BoxedRep Unlifted). But not TYPE IntRep, for example.
--- This levity-polymorphism comes from the use of the type variables
--- "v" and "w". See Note [Levity and representation polymorphic primops]
+-- (PE1) It is levity-polymorphic. It works for TYPE (BoxedRep Lifted) and
+-- TYPE (BoxedRep Unlifted). But not TYPE IntRep, for example.
+-- This levity-polymorphism comes from the use of the type variables
+-- "v" and "w". See Note [Levity and representation polymorphic primops]
--
--- * It does not evaluate its arguments. The user of the primop is responsible
--- for doing so.
+-- (PE2) It is hetero-typed; you can compare pointers of different types.
+-- This is used in various packages such as containers & unordered-containers.
--
--- * It is hetero-typed; you can compare pointers of different types.
--- This is used in various packages such as containers & unordered-containers.
+-- (PE3) It does not evaluate its arguments. The user of the primop is responsible
+-- for doing so. Consider
+-- let { x = p+q; y = q+p } in reallyUnsafePtrEquality# x y
+-- Here `x` and `y` point to different closures, so the expression will
+-- probably return False; but if `x` and/or `y` were evaluated for some
+-- other reason, then it might return True.
--
--- * It is obviously very dangerous, because
--- let x = f y in reallyUnsafePtrEquality# x x
--- will probably return True, whereas
--- reallyUnsafePtrEquality# (f y) (f y)
--- will probably return False. ("probably", because it's affected
--- by CSE and inlining).
+-- (PE4) It is obviously very dangerous, because replacing equals with equals
+-- in the program can change the result. For example
+-- let x = f y in reallyUnsafePtrEquality# x x
+-- will probably return True, whereas
+-- reallyUnsafePtrEquality# (f y) (f y)
+-- will probably return False. ("probably", because it's affected
+-- by CSE and inlining).
--
--- * reallyUnsafePtrEquality# can't fail, but it is marked as such
--- to prevent it from floating out.
--- See Note [reallyUnsafePtrEquality# can_fail]
+-- (PE5) reallyUnsafePtrEquality# can't fail, but it is marked as such
+-- to prevent it from floating out.
+-- See Note [reallyUnsafePtrEquality# can_fail]
--
--- The library GHC.Exts provides several less Wild-West functions
+-- The library GHC.Prim.PtrEq (and GHC.Exts) provides
+--
+-- unsafePtrEquality# ::
+-- forall (a :: UnliftedType) (b :: UnliftedType). a -> b -> Int#
+--
+-- It is still heterotyped (like (PE2)), but it's restricted to unlifted types
+-- (unlike (PE1)). That means that (PE3) doesn't apply: unlifted types are
+-- always evaluated, which makes it a bit less unsafe.
+--
+-- However unsafePtrEquality# is /implemented/ by a call to
+-- reallyUnsafePtrEquality#, so using the former is really just a documentation
+-- hint to the reader of the code. GHC behaves no differently.
+--
+-- The same library provides less Wild-West functions
-- for use in specific cases, namely:
--
-- reallyUnsafePtrEquality :: a -> a -> Int# -- not levity-polymorphic, nor hetero-typed
@@ -3469,7 +3487,7 @@ primop ReallyUnsafePtrEqualityOp "reallyUnsafePtrEquality#" GenPrimOp
-- sameIOPort# :: IOPort# s a -> IOPort# s a -> Int#
-- eqStableName# :: StableName# a -> StableName# b -> Int#
--
--- These operations are all specialisations of reallyUnsafePtrEquality#.
+-- These operations are all specialisations of unsafePtrEquality#.
-- Note [reallyUnsafePtrEquality# can_fail]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
=====================================
libraries/base/GHC/ArrayArray.hs
=====================================
@@ -49,6 +49,7 @@ module GHC.ArrayArray
where
import GHC.Prim
+import GHC.Prim.PtrEq ( unsafePtrEquality# )
import GHC.Types ( Type, UnliftedType, isTrue# )
import Unsafe.Coerce ( unsafeCoerce, unsafeCoerceUnlifted )
default ()
@@ -148,8 +149,8 @@ copyMutableArrayArray# = unsafeCoerce copyMutableArray#
-- | Compare the underlying pointers of two arrays of arrays.
sameArrayArray# :: ArrayArray# -> ArrayArray# -> Int#
-sameArrayArray# (ArrayArray# arr1) (ArrayArray# arr2) = reallyUnsafePtrEquality# arr1 arr2
+sameArrayArray# (ArrayArray# arr1) (ArrayArray# arr2) = unsafePtrEquality# arr1 arr2
-- | Compare the underlying pointers of two mutable arrays of arrays.
sameMutableArrayArray# :: MutableArrayArray# s -> MutableArrayArray# s -> Int#
-sameMutableArrayArray# (MutableArrayArray# marr1) (MutableArrayArray# marr2 ) = reallyUnsafePtrEquality# marr1 marr2
+sameMutableArrayArray# (MutableArrayArray# marr1) (MutableArrayArray# marr2 ) = unsafePtrEquality# marr1 marr2
=====================================
libraries/base/GHC/Exts.hs
=====================================
@@ -48,6 +48,7 @@ module GHC.Exts
-- ** Pointer comparison operations
-- See `Note [Pointer comparison operations]` in primops.txt.pp
reallyUnsafePtrEquality,
+ unsafePtrEquality#,
eqStableName#,
sameArray#,
sameMutableArray#,
=====================================
libraries/ghc-prim/GHC/Prim/PtrEq.hs
=====================================
@@ -1,6 +1,8 @@
{-# LANGUAGE Unsafe #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE MagicHash #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE KindSignatures #-}
-----------------------------------------------------------------------------
-- |
@@ -20,6 +22,7 @@
module GHC.Prim.PtrEq
( reallyUnsafePtrEquality,
+ unsafePtrEquality#,
sameArray#,
sameMutableArray#,
sameSmallArray#,
@@ -35,7 +38,7 @@ module GHC.Prim.PtrEq
) where
import GHC.Prim
-import GHC.Types () -- Make implicit dependency known to build system
+import GHC.Types (UnliftedType) -- Also make implicit dependency known to build system
default () -- Double and Integer aren't available yet
{- **********************************************************************
@@ -74,49 +77,62 @@ reallyUnsafePtrEquality = reallyUnsafePtrEquality#
-- See Note [Pointer comparison operations]
-- in primops.txt.pp
+-- | Compare the underlying pointers of two unlifted values for equality.
+--
+-- This is less dangerous than 'reallyUnsafePtrEquality',
+-- since the arguments are guaranteed to be evaluated.
+-- This means there is no risk of accidentally comparing
+-- a thunk.
+-- It's however still more dangerous than e.g. 'sameArray#'.
+--
+unsafePtrEquality# :: forall (a :: UnliftedType) (b :: UnliftedType). a -> b -> Int#
+unsafePtrEquality# = reallyUnsafePtrEquality#
+-- See Note [Pointer comparison operations]
+-- in primops.txt.pp
+
-- | Compare the underlying pointers of two arrays.
sameArray# :: Array# a -> Array# a -> Int#
-sameArray# = reallyUnsafePtrEquality#
+sameArray# = unsafePtrEquality#
-- | Compare the underlying pointers of two mutable arrays.
sameMutableArray# :: MutableArray# s a -> MutableArray# s a -> Int#
-sameMutableArray# = reallyUnsafePtrEquality#
+sameMutableArray# = unsafePtrEquality#
-- | Compare the underlying pointers of two small arrays.
sameSmallArray# :: SmallArray# a -> SmallArray# a -> Int#
-sameSmallArray# = reallyUnsafePtrEquality#
+sameSmallArray# = unsafePtrEquality#
-- | Compare the underlying pointers of two small mutable arrays.
sameSmallMutableArray# :: SmallMutableArray# s a -> SmallMutableArray# s a -> Int#
-sameSmallMutableArray# = reallyUnsafePtrEquality#
+sameSmallMutableArray# = unsafePtrEquality#
-- | Compare the pointers of two byte arrays.
sameByteArray# :: ByteArray# -> ByteArray# -> Int#
-sameByteArray# = reallyUnsafePtrEquality#
+sameByteArray# = unsafePtrEquality#
-- | Compare the underlying pointers of two mutable byte arrays.
sameMutableByteArray# :: MutableByteArray# s -> MutableByteArray# s -> Int#
-sameMutableByteArray# = reallyUnsafePtrEquality#
+sameMutableByteArray# = unsafePtrEquality#
-- | Compare the underlying pointers of two 'MutVar#'s.
sameMutVar# :: MutVar# s a -> MutVar# s a -> Int#
-sameMutVar# = reallyUnsafePtrEquality#
+sameMutVar# = unsafePtrEquality#
-- | Compare the underlying pointers of two 'TVar#'s.
sameTVar# :: TVar# s a -> TVar# s a -> Int#
-sameTVar# = reallyUnsafePtrEquality#
+sameTVar# = unsafePtrEquality#
-- | Compare the underlying pointers of two 'MVar#'s.
sameMVar# :: MVar# s a -> MVar# s a -> Int#
-sameMVar# = reallyUnsafePtrEquality#
+sameMVar# = unsafePtrEquality#
-- | Compare the underlying pointers of two 'IOPort#'s.
sameIOPort# :: IOPort# s a -> IOPort# s a -> Int#
-sameIOPort# = reallyUnsafePtrEquality#
+sameIOPort# = unsafePtrEquality#
-- | Compare the underlying pointers of two 'PromptTag#'s.
samePromptTag# :: PromptTag# a -> PromptTag# a -> Int#
-samePromptTag# = reallyUnsafePtrEquality#
+samePromptTag# = unsafePtrEquality#
-- Note [Comparing stable names]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -130,4 +146,4 @@ samePromptTag# = reallyUnsafePtrEquality#
-- | Compare two stable names for equality.
eqStableName# :: StableName# a -> StableName# b -> Int#
-eqStableName# = reallyUnsafePtrEquality#
+eqStableName# = unsafePtrEquality#
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9d61c182739c415f4283cca3c692e25c82b274f1
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9d61c182739c415f4283cca3c692e25c82b274f1
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