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

[Pranav Kant 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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pranavk wrote:

> Just to check my understanding, this property will prevent sections containing a GOT generating ADRP, or ADD/LDR relocation to a preemptible symbol from being folded. Even if the ADRP is separated into a different section, each "pair" of relocations will refer to the same folded symbol, so the GOT calculations will be correct.

That's my understanding as well. Symbols are not folded though. Folding happens at section-level. If each symbol is in its own section, their sections will be folded regardless if they contain preemptible or non-preemeptible symbols but any relocations pointing to such symbols won't be folded. Also, relocations are not rewritten. So they keep pointing to same symbols even if the section containing those symbols have been folded into some other section -- that's one of the reason we currently (excluding this patch) create GOT entries for all such `g*` symbols. We are parsing relocations and calling `addGotEntry` for every relocation target symbol we encounter. Later those GOT entries get `ABS` relocation which point to the canonical symbol/section. This way we end up with bunch of GOT entries that all look the same.

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