Add LTO build option #505
Add LTO build option #505
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An old PR which I used as a base: WebAssembly#150 Co-Authored-by: Dan Gohman <dev@sunfishcode.online>
| # 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 |
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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
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is it still necessary after https://reviews.llvm.org/D71738? do you have a test case?
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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.
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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).
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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)
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wasi-sdk counterpart WebAssembly/wasi-sdk#424 |
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can this land? |
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closed by mistake and then reopened. |
Makefile
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| @@ -627,6 +658,8 @@ $(SYSROOT_LIB)/libsetjmp.a: $(LIBSETJMP_OBJS) | |||
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| $(PIC_OBJS): CFLAGS += -fPIC -fvisibility=default | |||
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| $(LIBC_NONLTO_OBJS): CFLAGS += -fno-lto | |||
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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