There is a fundamental difference between how the gold API and lib/LTO view
the LTO process.
The gold API talks about a particular symbol in a particular file. The lib/LTO
API talks about a symbol in the merged module.
The merged module is then defined in terms of the IR semantics. In particular,
a linkonce_odr GV is only copied if it is used, since it is valid to drop
unused linkonce_odr GVs.
In the testcase in pr19901 both properties collide. What happens is that gold
asks us to keep a particular linkonce_odr symbol, but the IR linker doesn't
copy it to the merged module and we never have a chance to ask lib/LTO to keep
it.
This patch fixes it by having a more direct implementation of the gold API. If
it asks us to keep a symbol, we change the linkage so it is not linkonce. If it
says we can drop a symbol, we do so. All of this before we even send the module
to lib/Linker.
Since now we don't have to produce LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN,
during symbol resolution we can use a temporary LLVMContext and do lazy
module loading. This allows us to keep the minimum possible amount of
allocated memory around. This should also allow as much parallelism as
we want, since there is no shared context.
llvm-svn: 216215
The tools/lto API is not the best choice for implementing a gold plugin. Among
other issues:
* It is an stable ABI. Old errors stay and we have to be really careful
before adding new features.
* It has to support two fairly different linkers: gold and ld64.
* We end up with a plugin that depends on a shared lib, something quiet
unusual in LLVM land.
* It hides LLVM. For some features in the gold plugin it would be really
nice to be able to just get a Module or a GlobalValue.
This change is intended to be a very direct translation from the C API. It
will just enable other fixes and cleanups.
Tested with a LTO bootstrap on linux.
llvm-svn: 211315
The cmake build didn't support EXPORTED_SYMBOL_FILE. Instead, it had a
Windows-only implementation in tools/lto/CMakeLists.txt, a linux-only
implementation in tools/gold/CMakeLists.txt, and a darwin-only implementation
in tools/clang/tools/libclang/CMakeLists.txt.
This attempts to consolidate these one-offs into a single place. Clients can now
just set LLVM_EXPORTED_SYMBOL_FILE and things (hopefully) Just Work, like in
the make build.
llvm-svn: 198136
inconsistent with autoconf, which by default set BINUTILS_INCDIR to
empty and exclude gold from target list.
Based on a patch by Haitao Li!
llvm-svn: 131229
Rafael Espindola