[llvm] [Attributor] Pack out arguments into a struct (PR #119267)

[via llvm-commits]

elhewaty wrote:

@vidsinghal @arsenm,

What trying to do here, is creating a new variables instead of old argument args using allocas.

```
BasicBlock *EntryBlock = BasicBlock::Create(NewFunction->getContext(), "entry", NewFunction);
    IRBuilder<> EntryBuilder(EntryBlock);
    for (auto &OldArg : F.args()) {
      if (PtrToType.count(&OldArg)) {
        // The crash happens here, any hint?
        AllocaInst *Alloca = EntryBuilder.CreateAlloca(
            PtrToType[&OldArg], nullptr, OldArg.getName());
        EntryBuilder.CreateStore(&OldArg, Alloca);
        VMap[&OldArg] = Alloca;
      } else
        VMap[&OldArg] = &(*NewArgIt++);
    }
```

https://github.com/llvm/llvm-project/pull/119267