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602a5bbb32
It doesn't seem relevant to set an address space limit - this isn't important in any sense that I'm aware & it gets in the way of things that use a lot of address space, like llvm-symbolizer. This came up when I realized that bugpoint regression tests were much slower with -gsplit-dwarf than plain -g. Turned out that bugpoint subprocesses (opt, etc) were crashing and doing symbolization - but bugpoint runs those subprocesses with a 400MB memory limit. So with plain -g, mmaping the opt binary would exceed the memory limit, fail, and thus be really fast - no symbolization occurred. Whereas with -gsplit-dwarf, comically, having less to map in, it would succeed and then spend lots of time symbolizing. I've fixed at least the critical part of bugpoint's perf problem there by adding an option to allow bugpoint to disable symbolization. Thus improving the perfromance for -gsplit-dwarf and making the -g-esque speed available without this quirk/accidental benefit. llvm-svn: 305242
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