Partial fix for #2917

 - add newAlignedPinnedByteArray# for allocating pinned BAs with
   arbitrary alignment

 - the old newPinnedByteArray# now aligns to 16 bytes

Foreign.alloca will use newAlignedPinnedByteArray#, and so might end
up wasting less space than before (we used to align to 8 by default).
Foreign.allocaBytes and Foreign.mallocForeignPtrBytes will get 16-byte
aligned memory, which is enough to avoid problems with SSE
instructions on x86, for example.

There was a bug in the old newPinnedByteArray#: it aligned to 8 bytes,
but would have failed if the header was not a multiple of 8
(fortunately it always was, even with profiling).  Also we
occasionally wasted some space unnecessarily due to alignment in
allocatePinned().

I haven't done anything about Foreign.malloc/mallocBytes, which will
give you the same alignment guarantees as malloc() (8 bytes on
Linux/x86 here).

1 files changed, 1 insertions, 0 deletions

diff --git a/includes/StgMiscClosures.h b/includes/StgMiscClosures.h
index 94244a9a95..e2ec9e4d74 100644
--- a/includes/StgMiscClosures.h
+++ b/includes/StgMiscClosures.h
@@ -540,6 +540,7 @@ RTS_FUN(word64ToIntegerzh_fast);
 RTS_FUN(unsafeThawArrayzh_fast);
 RTS_FUN(newByteArrayzh_fast);
 RTS_FUN(newPinnedByteArrayzh_fast);
+RTS_FUN(newAlignedPinnedByteArrayzh_fast);
 RTS_FUN(newArrayzh_fast);
 
 RTS_FUN(newMutVarzh_fast);