[PATCH] D106213: [lld-macho] Enable copy-on-write for input buffers

[Duncan P. N. Exon Smith via Phabricator via llvm-commits]

dexonsmith added a comment.

In D106213#2905976 <https://reviews.llvm.org/D106213#2905976>, @int3 wrote:

> I am not able to get ld64 to dedup even the simplest of functions, let alone more complicated cases like these.

It's not safe to dedup symbols in general, since it's not always known if their addresses are compared.

Mach-O can be marked "autohide" or `.weak_def_can_be_hidden`, something LLVM sets on symbols when `GlobalValue::canBeOmittedFromSymbolTable` (see https://github.com/llvm/llvm-project/blob/main/llvm/lib/IR/Globals.cpp#L311 or grep for `MCSA_WeakDefAutoPrivate`) -- that is, when a symbol is `linkonce_odr` and `unnamed_addr`. GlobalVariables that are also `const` can just be `local_unnamed_addr`. For C++ code, this should be true for most inlines and templates.

ld64 reuses this autohide flag to trigger dedup only when it's safe.


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https://reviews.llvm.org/D106213