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| author | Andrew Martin <andrew.thaddeus@gmail.com> | 2019-11-13 11:20:05 -0500 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2020-05-23 13:37:01 -0400 |
| commit | 49301ad6226d9a83d110bee8c419615dd94f5ded (patch) | |
| tree | 907c00e2c81d1f2025ad569cedf2bc39833bcb07 /libraries/ghc-prim | |
| parent | d830bbc9921bcc59164a0a18f0e0874ae4ce226e (diff) | |
| download | haskell-49301ad6226d9a83d110bee8c419615dd94f5ded.tar.gz | |
Implement cstringLength# and FinalPtr
This function and its accompanying rule resolve issue #5218.
A future PR to the bytestring library will make the internal
Data.ByteString.Internal.unsafePackAddress compute string length
with cstringLength#. This will improve the status quo because it is
eligible for constant folding.
Additionally, introduce a new data constructor to ForeignPtrContents
named FinalPtr. This additional data constructor, when used in the
IsString instance for ByteString, leads to more Core-to-Core
optimization opportunities, fewer runtime allocations, and smaller
binaries.
Also, this commit re-exports all the functions from GHC.CString
(including cstringLength#) in GHC.Exts. It also adds a new test
driver. This test driver is used to perform substring matches on Core
that is dumped after all the simplifier passes. In this commit, it is
used to check that constant folding of cstringLength# works.
Diffstat (limited to 'libraries/ghc-prim')
| -rw-r--r-- | libraries/ghc-prim/GHC/CString.hs | 19 | ||||
| -rw-r--r-- | libraries/ghc-prim/changelog.md | 8 |
2 files changed, 24 insertions, 3 deletions
diff --git a/libraries/ghc-prim/GHC/CString.hs b/libraries/ghc-prim/GHC/CString.hs index 8c0d272a67..514fb0e9f9 100644 --- a/libraries/ghc-prim/GHC/CString.hs +++ b/libraries/ghc-prim/GHC/CString.hs @@ -1,5 +1,4 @@ -{-# LANGUAGE MagicHash, NoImplicitPrelude, BangPatterns #-} - +{-# LANGUAGE MagicHash, NoImplicitPrelude, BangPatterns, UnliftedFFITypes #-} ----------------------------------------------------------------------------- -- | -- Module : GHC.CString @@ -18,7 +17,7 @@ module GHC.CString ( unpackCString#, unpackAppendCString#, unpackFoldrCString#, - unpackCStringUtf8#, unpackNBytes# + unpackCStringUtf8#, unpackNBytes#, cstringLength# ) where import GHC.Types @@ -174,3 +173,17 @@ unpackNBytes# addr len# = unpack [] (len# -# 1#) case indexCharOffAddr# addr i# of ch -> unpack (C# ch : acc) (i# -# 1#) +-- The return type is not correct here. We really want CSize, +-- but that type is defined in base. However, CSize should always +-- match the size of a machine word (I hope), so this is probably +-- alright on all platforms that GHC supports. +foreign import ccall unsafe "strlen" c_strlen :: Addr# -> Int# + +-- | Compute the length of a NUL-terminated string. This address +-- must refer to immutable memory. GHC includes a built-in rule for +-- constant folding when the argument is a statically-known literal. +-- That is, a core-to-core pass reduces the expression +-- @cstringLength# "hello"#@ to the constant @5#@. +cstringLength# :: Addr# -> Int# +{-# INLINE[0] cstringLength# #-} +cstringLength# = c_strlen diff --git a/libraries/ghc-prim/changelog.md b/libraries/ghc-prim/changelog.md index cf14d21c81..9cfbe99dbe 100644 --- a/libraries/ghc-prim/changelog.md +++ b/libraries/ghc-prim/changelog.md @@ -1,3 +1,11 @@ +## 0.6.2 (edit as necessary) + +- Shipped with GHC 8.12.1 + +- Add known-key `cstringLength#` to `GHC.CString`. This is just the + C function `strlen`, but a built-in rewrite rule allows GHC to + compute the result at compile time when the argument is known. + ## 0.6.1 (edit as necessary) - Shipped with GHC 8.10.1 |