[lld] [llvm] [DTLTO] Improve performance of adding files to the link (PR #186366)

[Teresa Johnson via llvm-commits]

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@@ -367,13 +367,16 @@ LLVM_ABI ThinBackend createInProcessThinBackend(
 /// backend compilations.
 /// SaveTemps is a debugging tool that prevents temporary files created by this
 /// backend from being cleaned up.
+/// AddBuffer is optional. If provided, it is used to add the externally
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teresajohnson wrote:

Why make it optional? The only other caller is in llvm-lto2 and I suggest passing the AddBuffer it is creating for caching to this call from there too, which also gives the benefit of more testing.

https://github.com/llvm/llvm-project/pull/186366