Don't export upstream monomorphizations from compiler-builtins

[saethlin]

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[saethlin]

r? bjorn3

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r? @JonathanBrouwer

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[saethlin]

🤨

r? bjorn3

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[durin42]

Patched it in and built a toolchain so I could test it on my Mac, and as far as I can tell this does fix the problem. Thanks for a quick fix!

[bjorn3]

Alternatively could we avoid returning anything from exported_generic_symbols when building compiler-builtins? All symbols in compiler-builtins have hidden visibility and as such we don't tell the linker to export them either.

Also does this PR mean the special case at

rust/compiler/rustc_middle/src/ty/instance.rs

Lines 222 to 225 in 838a912

	// compiler_builtins cannot use upstream monomorphizations.
	if tcx.is_compiler_builtins(LOCAL_CRATE) {
	return None;
	}

can be removed?

[saethlin]

Alternatively could we avoid returning anything from exported_generic_symbols when building compiler-builtins?

This occurred to me as well as I was falling asleep. I'll try it out.

[saethlin]

Also does this PR mean the special case at

I don't think that special case can be removed, because that is supposed to block compiler-builtins from calling into a monomorphization exported by core.