Don't internalize symbols used by global_asm
#97900
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Symbols that are only reachable from the current CGU have their visibility changed to internal to allow LLVM to better optimize them. However this doesn't work for symbols that are used in `global_asm!`: the symbol name is inserted into the assembly code as text, which LLVM is not aware of. In particular, LLVM may delete the symbol in the MergeFunctions pass if it can't see any other uses of it. The solution here is to ensure that symbols used by `global_asm!` are always marked with external linkage. Fixes rust-lang#96797
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nbdd0121
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Jun 8, 2022
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I'm actually looking at a potential fix in LLVM instead. Marking as draft for now. |
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Ping me if the LLVM patch doesn't gain traction, although I think someone else in t-compiler should review this. |
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Closing in favor of LLVM patch: https://reviews.llvm.org/D127751 |
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Symbols that are only reachable from the current CGU have their
visibility changed to internal to allow LLVM to better optimize them.
However this doesn't work for symbols that are used in
global_asm!:the symbol name is inserted into the assembly code as text, which LLVM
is not aware of. In particular, LLVM may delete the symbol in the
MergeFunctions pass if it can't see any other uses of it.
The solution here is to ensure that symbols used by
global_asm!arealways marked with external linkage.
Fixes #96797
cc @nbdd0121