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Pavel Labath
802e2f30e4
Summary: This kind of functionality is useful to other project apart from clang. LLDB works with version numbers a lot, but it does not have a convenient abstraction for this. Moving this class to a lower level library allows it to be freely used within LLDB. Since this class is used in a lot of places in clang, and it used to be in the clang namespace, it seemed appropriate to add it to the list of adopted classes in LLVM.h to avoid prefixing all uses with "llvm::". Also, I didn't find any tests specific for this class, so I wrote a couple of quick ones for the more interesting bits of functionality. Reviewers: zturner, erik.pilkington Subscribers: mgorny, cfe-commits, llvm-commits Differential Revision: https://reviews.llvm.org/D47887 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@334399 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