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415a008ad2
BumpPtrAllocator significantly less strange by making it a simple function of the number of slabs allocated rather than by making it a recurrance. I *think* the previous behavior was essentially that the size of the slabs would be doubled after the first 128 were allocated, and then doubled again each time 64 more were allocated, but only if every allocation packed perfectly into the slab size. If not, the wasted space wouldn't be counted toward increasing the size, but allocations over the size threshold *would*. And since the allocations over the size threshold might be much larger than the slab size, this could have somewhat surprising consequences where we rapidly grow the slab size. This currently requires adding state to the allocator to track the number of slabs currently allocated, but that isn't too bad. I'm planning further changes to the allocator that will make this state fall out even more naturally. It still doesn't fully decouple the growth rate from the allocations which are over the size threshold. That fix is coming later. This specific fix will allow making the entire thing into a more stateless device and lifting the parameters into template parameters rather than runtime parameters. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204993 91177308-0d34-0410-b5e6-96231b3b80d8
Design Of lib/System
====================
The software in this directory is designed to completely shield LLVM from any
and all operating system specific functionality. It is not intended to be a
complete operating system wrapper (such as ACE), but only to provide the
functionality necessary to support LLVM.
The software located here, of necessity, has very specific and stringent design
rules. Violation of these rules means that cracks in the shield could form and
the primary goal of the library is defeated. By consistently using this library,
LLVM becomes more easily ported to new platforms since the only thing requiring
porting is this library.
Complete documentation for the library can be found in the file:
llvm/docs/SystemLibrary.html
or at this URL:
http://llvm.org/docs/SystemLibrary.html
While we recommend that you read the more detailed documentation, for the
impatient, here's a high level summary of the library's requirements.
1. No system header files are to be exposed through the interface.
2. Std C++ and Std C header files are okay to be exposed through the interface.
3. No exposed system-specific functions.
4. No exposed system-specific data.
5. Data in lib/System classes must use only simple C++ intrinsic types.
6. Errors are handled by returning "true" and setting an optional std::string
7. Library must not throw any exceptions, period.
8. Interface functions must not have throw() specifications.
9. No duplicate function impementations are permitted within an operating
system class.
To accomplish these requirements, the library has numerous design criteria that
must be satisfied. Here's a high level summary of the library's design criteria:
1. No unused functionality (only what LLVM needs)
2. High-Level Interfaces
3. Use Opaque Classes
4. Common Implementations
5. Multiple Implementations
6. Minimize Memory Allocation
7. No Virtual Methods