[Attributor] Use byval type instead of pointer element type

[nikic]

Summary

Use the byval type for compatibility with opaque pointers. Putting this up for review as I'm not sure whether I'm using the Attributor APIs correctly here.

[jdoerfert]

LG, assuming this passes our tests.

[nikic]

This landed in https://github.com/llvm/llvm-project/commit/f682a8386b5aa0fcc09754bf5a08cbe43d33065e, but I used the wrong tag line...

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

struct AAPrivatizablePtrArgument final : public AAPrivatizablePtrImpl {
   AAPrivatizablePtrArgument(const IRPosition &IRP, Attributor &A)
       : AAPrivatizablePtrImpl(IRP, A) {}
 
   /// See AAPrivatizablePtrImpl::identifyPrivatizableType(...)
   Optional<Type *> identifyPrivatizableType(Attributor &A) override {
     // If this is a byval argument and we know all the call sites (so we can
     // rewrite them), there is no need to check them explicitly.
     bool UsedAssumedInformation = false;
-    if (getIRPosition().hasAttr(Attribute::ByVal) &&
+    SmallVector<Attribute, 1> Attrs;
+    getAttrs({Attribute::ByVal}, Attrs, /* IgnoreSubsumingPositions */ true);
+    if (!Attrs.empty() &&
         A.checkForAllCallSites([](AbstractCallSite ACS) { return true; }, *this,
                                true, UsedAssumedInformation))
-      return getAssociatedValue().getType()->getPointerElementType();
+      return Attrs[0].getValueAsType();
 
     Optional<Type *> Ty;
     unsigned ArgNo = getIRPosition().getCallSiteArgNo();
 
     // Make sure the associated call site argument has the same type at all call
     // sites and it is an allocation we know is safe to privatize, for now that
     // means we only allow alloca instructions.
     // TODO: We can additionally analyze the accesses in the callee to  create
Optional<Type *> identifyPrivatizableType(Attributor &A) override {
     if (auto *AI = dyn_cast<AllocaInst>(Obj))
       if (auto *CI = dyn_cast<ConstantInt>(AI->getArraySize()))
         if (CI->isOne())
           return AI->getAllocatedType();
     if (auto *Arg = dyn_cast<Argument>(Obj)) {
       auto &PrivArgAA = A.getAAFor<AAPrivatizablePtr>(
           *this, IRPosition::argument(*Arg), DepClassTy::REQUIRED);
       if (PrivArgAA.isAssumedPrivatizablePtr())
-        return Obj->getType()->getPointerElementType();
+        return PrivArgAA.getPrivatizableType();
     }
 
     LLVM_DEBUG(dbgs() << "[AAPrivatizablePtr] Underlying object neither valid "
                          "alloca nor privatizable argument: "
                       << *Obj << "!\n");
     return nullptr;
   }