Commit 404bf05e authored by Ben Gamari's avatar Ben Gamari 🐢

base: Make Foreign.Marshal.Alloc.allocBytes[Aligned] NOINLINE

As noted in #14346, touch# may be optimized away when the simplifier can see
that the continuation passed to allocaBytes will not return. Marking CPS-style
functions with NOINLINE ensures that the simplier can't draw any unsound
conclusions.

Ultimately the right solution here will be to do away with touch# and instead
introduce a scoped primitive as is suggested in #14375.
parent cb7f91db
......@@ -123,6 +123,19 @@ alloca = doAlloca undefined
doAlloca :: Storable a' => a' -> (Ptr a' -> IO b') -> IO b'
doAlloca dummy = allocaBytesAligned (sizeOf dummy) (alignment dummy)
-- Note [NOINLINE for touch#]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Both allocaBytes and allocaBytesAligned use the touch#, which is notoriously
-- fragile in the presence of simplification (see #14346). In particular, the
-- simplifier may drop the continuation containing the touch# if it can prove
-- that the action passed to allocaBytes will not return. The hack introduced to
-- fix this for 8.2.2 is to mark allocaBytes as NOINLINE, ensuring that the
-- simplifier can't see the divergence.
--
-- These can be removed once #14375 is fixed, which suggests that we instead do
-- away with touch# in favor of a primitive that will capture the scoping left
-- implicit in the case of touch#.
-- |@'allocaBytes' n f@ executes the computation @f@, passing as argument
-- a pointer to a temporarily allocated block of memory of @n@ bytes.
-- The block of memory is sufficiently aligned for any of the basic
......@@ -141,6 +154,8 @@ allocaBytes (I# size) action = IO $ \ s0 ->
case touch# barr# s3 of { s4 ->
(# s4, r #)
}}}}}
-- See Note [NOINLINE for touch#]
{-# NOINLINE allocaBytes #-}
allocaBytesAligned :: Int -> Int -> (Ptr a -> IO b) -> IO b
allocaBytesAligned (I# size) (I# align) action = IO $ \ s0 ->
......@@ -152,6 +167,8 @@ allocaBytesAligned (I# size) (I# align) action = IO $ \ s0 ->
case touch# barr# s3 of { s4 ->
(# s4, r #)
}}}}}
-- See Note [NOINLINE for touch#]
{-# NOINLINE allocaBytesAligned #-}
-- |Resize a memory area that was allocated with 'malloc' or 'mallocBytes'
-- to the size needed to store values of type @b@. The returned pointer
......
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