[llvm] [BOLT][AArch64] Relax calls and branches with fragment clusters (PR #215825)

[Rafael Auler via llvm-commits]

rafaelauler wrote:

@labrinea 

I tested this new stack but it broke for me and generated out-of-range calls, I bisected the problem to commit "refactor branch collection and get rid of relax-plt". It dropped the containment guard from the adjacent-cluster long-thunk reuse:

         if (ReuseCluster) {
           auto It = ReuseCluster->CallThunks.find(TargetSymbol);
  -        if (It != ReuseCluster->CallThunks.end() &&
  -            llvm::is_contained(*ReuseThunkList, It->second)) {
  +        if (It != ReuseCluster->CallThunks.end()) {
             BinaryFunction *Thunk = It->second;

That guard was the "only reuse if the neighbor actually hosts this thunk" check. Without it, reuse becomes transitive.

https://github.com/llvm/llvm-project/pull/215825