Revert "[IPO] Added attributor for identifying invariant loads" (#144808)

Reverts #141800

The implementation critically misunderstands the `AAMemoryBehavior`
attributor, which it relies on heavily.

@shiltian, since I do not have commit permissions.

Author: zGoldthorpe

llvm/include/llvm/Transforms/IPO/Attributor.h

@@ -6335,47 +6335,6 @@ struct AAUnderlyingObjects : AbstractAttribute {
                           AA::ValueScope Scope = AA::Interprocedural) const = 0;
 };
 
-/// An abstract interface for identifying pointers from which loads can be
-/// marked invariant.
-struct AAInvariantLoadPointer : public AbstractAttribute {
-  AAInvariantLoadPointer(const IRPosition &IRP) : AbstractAttribute(IRP) {}
-
-  /// See AbstractAttribute::isValidIRPositionForInit
-  static bool isValidIRPositionForInit(Attributor &A, const IRPosition &IRP) {
-    if (!IRP.getAssociatedType()->isPointerTy())
-      return false;
-
-    return AbstractAttribute::isValidIRPositionForInit(A, IRP);
-  }
-
-  /// Create an abstract attribute view for the position \p IRP.
-  static AAInvariantLoadPointer &createForPosition(const IRPosition &IRP,
-                                                   Attributor &A);
-
-  /// Return true if the pointer's contents are known to remain invariant.
-  virtual bool isKnownInvariant() const = 0;
-  virtual bool isKnownLocallyInvariant() const = 0;
-
-  /// Return true if the pointer's contents are assumed to remain invariant.
-  virtual bool isAssumedInvariant() const = 0;
-  virtual bool isAssumedLocallyInvariant() const = 0;
-
-  /// See AbstractAttribute::getName().
-  StringRef getName() const override { return "AAInvariantLoadPointer"; }
-
-  /// See AbstractAttribute::getIdAddr().
-  const char *getIdAddr() const override { return &ID; }
-
-  /// This function should return true if the type of the \p AA is
-  /// AAInvariantLoadPointer
-  static bool classof(const AbstractAttribute *AA) {
-    return (AA->getIdAddr() == &ID);
-  }
-
-  /// Unique ID (due to the unique address).
-  static const char ID;
-};
-
 /// An abstract interface for address space information.
 struct AAAddressSpace : public StateWrapper<BooleanState, AbstractAttribute> {
   AAAddressSpace(const IRPosition &IRP, Attributor &A)

llvm/lib/Transforms/IPO/Attributor.cpp

@@ -3612,8 +3612,6 @@ void Attributor::identifyDefaultAbstractAttributes(Function &F) {
       if (SimplifyAllLoads)
         getAssumedSimplified(IRPosition::value(I), nullptr,
                              UsedAssumedInformation, AA::Intraprocedural);
-      getOrCreateAAFor<AAInvariantLoadPointer>(
-          IRPosition::value(*LI->getPointerOperand()));
       getOrCreateAAFor<AAAddressSpace>(
           IRPosition::value(*LI->getPointerOperand()));
     } else {