llvm-6502/lib/System/README.txt
Reid Spencer 99655e16a6 For PR797:
Final commit for this bug. This removes the last EH holdouts in LLVM
and turns off exception support by using the -fno-exceptions option. This
leads to the following reduction in library and executable sizes:
                DEBUG BUILD                RELEASE BUILD
         before     after   delta     before   after    delta
lib    162,328K  157,616K   4,712    17,864K  16,416K  1,448K
bin    571,444K  557,156K  14,288    63,296K   56,996K 6,300K

Debug   Improvement: 19,000K (2.59%)
Release Improvement:  7,748K (9.55%)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29882 91177308-0d34-0410-b5e6-96231b3b80d8
2006-08-25 19:54:53 +00:00

44 lines
1.9 KiB
Plaintext

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</a></li>
5. Multiple Implementations</a></li>
6. Minimize Memory Allocation</a></li>
7. No Virtual Methods