Instead of aligning and moving the CurPtr forward, and then comparing
with End, simply calculate how much space is needed, and compare that
to how much is available.
Hopefully this avoids any doubts about comparing addresses possibly
derived from past the end of the slab array, overflowing, etc.
Also add a test where aligning CurPtr would move it past End.
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In theory, alignPtr() could push a pointer beyond the end of the current slab, making
comparisons with that pointer undefined behaviour. Use an integer type to avoid this.
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We already handle the no-slabs case when checking whether the current slab
is large enough: if no slabs have been allocated, CurPtr and End are both 0.
alignPtr(0), will still be 0, and so "if (Ptr + Size <= End)" fails.
Differential Revision: http://reviews.llvm.org/D4943
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by removing the MallocSlabAllocator entirely and just using
MallocAllocator directly. This makes all off these allocators expose and
utilize the same core interface.
The only ugly part of this is that it exposes the fact that the JIT
allocator has no real handling of alignment, any more than the malloc
allocator does. =/ It would be nice to fix both of these to support
alignments, and then to leverage that in the BumpPtrAllocator to do less
over allocation in order to manually align pointers. But, that's another
patch for another day. This patch has no functional impact, it just
removes the somewhat meaningless wrapper around MallocAllocator.
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abstract interface. The only user of this functionality is the JIT
memory manager and it is quite happy to have a custom type here. This
removes a virtual function call and a lot of unnecessary abstraction
from the common case where this is just a *very* thin vaneer around
a call to malloc.
Hopefully still no functionality changed here. =]
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slabs rather than embedding a singly linked list in the slabs
themselves. This has a few advantages:
- Better utilization of the slab's memory by not wasting 16-bytes at the
front.
- Simpler allocation strategy by not having a struct packed at the
front.
- Avoids paging every allocated slab in just to traverse them for
deallocating or dumping stats.
The latter is the really nice part. Folks have complained from time to
time bitterly that tearing down a BumpPtrAllocator, even if it doesn't
run any destructors, pages in all of the memory allocated. Now it won't.
=]
Also resolves a FIXME with the scaling of the slab sizes. The scaling
now disregards specially sized slabs for allocations larger than the
threshold.
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parameters rather than runtime parameters.
There is only one user of these parameters and they are compile time for
that user. Making these compile time seems to better reflect their
intended usage as well.
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Now to copy a string into a BumpPtrAllocator and get a StringRef to the copy:
StringRef myCopy = myStr.copy(myAllocator);
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malloc, so there should be no functional changes to other code.
These changes are necessary since I have plans to use this allocator in the JIT
memory manager, and it needs a special allocator.
I also added some tests which helped me pinpoint some bugs.
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