[PATCH] D127751: [MergeFunctions] Preserve symbols used llvm.used/llvm.compiler.used

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

We can't rename or erase a function used by `@llvm.used`; the symbol has to exist for use by inline asm etc.  So this is correct in that respect.



================
Comment at: llvm/lib/Transforms/IPO/MergeFunctions.cpp:841
+      // usually from inline asm.
+      if (G->hasGlobalUnnamedAddr() && !Used.contains(G)) {
         // G might have been a key in our GlobalNumberState, and it's illegal
----------------
I'm a bit suspicious of the hasGlobalUnnamedAddr() check here.  hasGlobalUnnamedAddr() generally implies it's legal to merge two constants/functions, but we don't actually figure out if we're going to perform an actual merge at this point; that doesn't happen until we try to discard it, or call writeThunkOrAlias.  (unnamed_addr only allows rewriting all the uses of a variable/function at once, not just some of them.  Otherwise you end up with weird inconsistencies where a value isn't equal to itself.)


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https://reviews.llvm.org/D127751