[commit: ghc] master: Implement new `compareByteArrays#` primop (e3ba26f)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/e3ba26f8b49700b41ff4672f3f7f6a4e453acdcc/ghc

>---------------------------------------------------------------

commit e3ba26f8b49700b41ff4672f3f7f6a4e453acdcc
Author: Herbert Valerio Riedel <hvr at gnu.org>
Date:   Mon Oct 16 21:01:57 2017 +0200

    Implement new `compareByteArrays#` primop
    
    The new primop
    
        compareByteArrays# :: ByteArray# -> Int# {- offset -}
                           -> ByteArray# -> Int# {- offset -}
                           -> Int# {- length -}
                           -> Int#
    
    allows to compare the subrange of the first `ByteArray#` to
    the (same-length) subrange of the second `ByteArray#` and returns a
    value less than, equal to, or greater than zero if the range is found,
    respectively, to be byte-wise lexicographically less than, to match,
    or be greater than the second range.
    
    Under the hood, the new primop is implemented in terms of the standard
    ISO C `memcmp(3)` function. It is currently an out-of-line primop but
    work is underway to optimise this into an inline primop for a future
    follow-up Differential (see D4091).
    
    This primop has applications in packages like `text`, `text-short`,
    `bytestring`, `text-containers`, `primitive`, etc.  which currently
    have to incur the overhead of an ordinary FFI call to directly or
    indirectly invoke `memcmp(3)` as well has having to deal with some
    `unsafePerformIO`-variant.
    
    While at it, this also improves the documentation for the existing
    `copyByteArray#` primitive which has a non-trivial type-signature
    that significantly benefits from a more explicit description of its
    arguments.
    
    Reviewed By: bgamari
    
    Differential Revision: https://phabricator.haskell.org/D4090


>---------------------------------------------------------------

e3ba26f8b49700b41ff4672f3f7f6a4e453acdcc
 compiler/prelude/primops.txt.pp                    |  25 ++-
 includes/stg/MiscClosures.h                        |   1 +
 rts/PrimOps.cmm                                    |  14 ++
 rts/RtsSymbols.c                                   |   1 +
 testsuite/tests/codeGen/should_run/all.T           |   1 +
 .../tests/codeGen/should_run/compareByteArrays.hs  | 167 +++++++++++++++++++++
 .../codeGen/should_run/compareByteArrays.stdout    |  12 ++
 7 files changed, 218 insertions(+), 3 deletions(-)

Diff suppressed because of size. To see it, use:

    git diff-tree --root --patch-with-stat --no-color --find-copies-harder --ignore-space-at-eol --cc e3ba26f8b49700b41ff4672f3f7f6a4e453acdcc