Add LTO build option #505
Add LTO build option #505
Conversation
An old PR which I used as a base: WebAssembly#150 Co-Authored-by: Dan Gohman <[email protected]>
| # LTO; no, full, or thin | ||
| # Note: thin LTO here is just for experimentation. It has known issues: | ||
| # - https://github.com/llvm/llvm-project/issues/91700 | ||
| # - https://github.com/llvm/llvm-project/issues/91711 |
There was a problem hiding this comment.
In addition to these issue I think you will find that any symbols that implement libcalls, or required by the libcall implemenation must currently be excluded from LTO. See https://github.com/emscripten-core/emscripten/blob/3de1b9091adbadc46706959bd97efa033214bc2c/tools/system_libs.py#L1007-L1020
There was a problem hiding this comment.
is it still necessary after https://reviews.llvm.org/D71738? do you have a test case?
There was a problem hiding this comment.
i have excluded __cxa_atexit since then.
other things listed in your emscripten link seem like compiler-rt, which i don't have a plan to build with LTO for now.
There was a problem hiding this comment.
I think one issue is that compiler-rt can have transitive dependencies into libc. I imagine you will run into similar issues here once you start testing more extensively with LTO, but perhaps I'm wrong, or perhaps things have changed in some way.
Anyway, I guess its fine to land this and then fix issues as they come up in the field (which is basically what we did in emscripten).
There was a problem hiding this comment.
i glanced at compiler-rt.
i couldn't find problematic transitive dependencies.
obvious dependencies like memset etc are covered by https://reviews.llvm.org/D71738.
This fixes a failure in wasi-sdk "make check".
("undefined symbol: __cxa_atexit" for ctors_dtors.c test)
|
wasi-sdk counterpart WebAssembly/wasi-sdk#424 |
|
can this land? |
|
closed by mistake and then reopened. |
Makefile
Outdated
| @@ -627,6 +658,8 @@ $(SYSROOT_LIB)/libsetjmp.a: $(LIBSETJMP_OBJS) | |||
|
|
|||
| $(PIC_OBJS): CFLAGS += -fPIC -fvisibility=default | |||
|
|
|||
| $(LIBC_NONLTO_OBJS): CFLAGS += -fno-lto | |||
There was a problem hiding this comment.
nit: I wonder if we could instead filter out the -flto flag instead of passing both -flto and -fno-lto?
cmake version WebAssembly/wasi-sdk#436 |
An old PR which I used as a base:
#150