[lld] [lld][ELF] Merge equivalent symbols found during ICF (PR #139493)

[Hans Wennborg via llvm-commits]

================
@@ -286,9 +313,14 @@ bool ICF<ELFT>::constantEq(const InputSection *secA, Relocs<RelTy> ra,
     // Relocations referring to InputSections are constant-equal if their
     // section offsets are equal.
     if (isa<InputSection>(da->section)) {
-      if (da->value + addA == db->value + addB)
+      if (da->value + addA == db->value + addB) {
----------------
zmodem wrote:

I may be misremembering, but IIRC the only size impact we complained about was from the suggested workaround of using `--icf=safe`.

I don't remember evaluating the size impact of this PR. We just tried it and confirmed it works (https://crbug.com/415810137#comment50), waited for it to get through review, and reverted the original change as the fix seemed to be taking a while.

https://github.com/llvm/llvm-project/pull/139493