fe1ffb912d
CALL_ONCE_... macro in the legacy pass manager with the new llvm::call_once facility. Nothing changed sicne the last attempt in r271781 which I reverted in r271788. At least one of the failures I saw was spurious, and I want to make sure the other failures are real before I work around them -- they appeared to only effect ppc64le and ppc64be. Original commit message of r271781: ---- [LPM] Reinstate r271652 to replace the CALL_ONCE_... macro in the legacy pass manager with the new llvm::call_once facility. This reverts commit r271657 and re-applies r271652 with a fix to actually work with arguments. In the original version, we just ended up directly calling std::call_once via ADL because of the std::once_flag argument. The llvm::call_once never worked with arguments. Now, llvm::call_once is a variadic template that perfectly forwards everything. As a part of this it had to move to the header and we use a generic functor rather than an explict function pointer. It would be nice to use std::invoke here but we don't have it yet. That means pointer to members won't work here, but that seems a tolerable compromise. I've also tested this by forcing the fallback path, so hopefully it sticks this time. ---- Original commit message of r271652: ---- [LPM] Replace the CALL_ONCE_... macro in the legacy pass manager with the new llvm::call_once facility. This facility matches the standard APIs and when the platform supports it actually directly uses the standard provided functionality. This is both more efficient on some platforms and much more TSan friendly. The only remaining user of the cas_flag and home-rolled atomics is the fallback implementation of call_once. I have a patch that removes them entirely, but it needs a Windows patch to land first. This alone substantially cleans up the macros for the legacy pass manager, and should subsume some of the work Mehdi was doing to clear the path for TSan testing of ThinLTO, a really important step to have reliable upstream testing of ThinLTO in all forms. ---- llvm-svn: 271800
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