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7acd886ecf
The idea of this patch is to turn llvm/Support/system_error.h into a transitional header that just brings in the erorr_code api to the llvm namespace. I will remove it shortly afterwards. The cases where the general idea needed some tweaking: * std::errc is a namespace in msvc, so we cannot use "using std::errc". I could add an #ifdef, but there were not that many uses, so I just added std:: to them in this patch. * Template specialization had to be moved to the std namespace in this patch set already. * The msvc implementation of default_error_condition doesn't seem to provide the same transformations as we need. Not too surprising since the standard doesn't actually say what "equivalent" means. I fixed the problem by keeping our old mapping and using it at error_code construction time. Despite these shortcomings I think this is still a good thing. Some reasons: * The different implementations of system_error might improve over time. * It removes 925 lines of code from llvm already. * It removes 6313 bytes from the text segment of the clang binary when it is built with gcc and 2816 bytes when building with clang and libstdc++. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210687 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