[lld] [lld] Merge GOT entries for symbols that have been ICFed (PR #131630)

[Peter Collingbourne via llvm-commits]

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@@ -667,6 +667,20 @@ GotSection::GotSection(Ctx &ctx)
 void GotSection::addConstant(const Relocation &r) { relocations.push_back(r); }
 void GotSection::addEntry(const Symbol &sym) {
   assert(sym.auxIdx == ctx.symAux.size() - 1);
+  auto *d = dyn_cast<Defined>(&sym);
+  if (d && ctx.arg.icf != ICFLevel::None) {
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pcc wrote:

That prevents ICF on the sections containing the relocation but not the target sections. Also, it is not necessary for ICF to have been applied to target sections in order to end up with symbols with the same section/value. Consider:
```
.globl f1, f2
f1:
f2:
ret
```
We do not want `f1` and `f2` to have the same GOT entry.

https://github.com/llvm/llvm-project/pull/131630