[llvm-commits] [llvm] r151834 - in /llvm/trunk: lib/Support/Allocator.cpp unittests/Support/AllocatorTest.cpp

[Chris Lattner]

On Mar 1, 2012, at 1:14 PM, Argyrios Kyrtzidis wrote:
>>> void *BumpPtrAllocator::Allocate(size_t Size, size_t Alignment) {
>>> +  // 0-byte alignment means 1-byte alignment.
>>> +  if (Alignment == 0) Alignment = 1;
>>> +
>>> +  size_t PaddedSize = Size + sizeof(MemSlab) + Alignment - 1;
>>> +
>>> +  // If requested size exceeds slab size, increase slab size.
>>> +  while (PaddedSize > SlabSize)
>>> +    SlabSize *= 2;
>> 
>> Have you measured that this doesn't make us waste a ton of memory?
> 
> Without my change BumpPtrAllocator will just corrupt memory when "PaddedSize > SlabSize"; do you have an alternative way in mind to handle this ?

Why not have it just handle "allocation request greater than the slab size" as doing a separate allocation just for that request (and tracking it as a slab) but not changing the slab size?

Given an allocation pattern like:

alloc(4)
alloc(4)
alloc(4)
alloc(40000000)
alloc(4)

It would be nice to have this end up as two slabs: the initial one and the one very-large one.

-Chris