Index: llvm/include/llvm/Transforms/IPO/Attributor.h
===================================================================
--- llvm/include/llvm/Transforms/IPO/Attributor.h
+++ llvm/include/llvm/Transforms/IPO/Attributor.h
@@ -655,9 +655,17 @@
   int AttributeIdx;
 };
 
+/// Helper struct necessary as the modular build fails if the virtual method
+/// IRAttribute::manifest is defined in the Attributor.cpp.
+struct IRAttributeManifest {
+  static ChangeStatus manifestAttrs(Attributor &A, IRPosition &IRP,
+      const ArrayRef<Attribute> &DeducedAttrs);
+};
+
 /// Helper class that provides common functionality to manifest IR attributes.
 template <Attribute::AttrKind AK, typename Base>
-struct IRAttribute : public IRPosition, public Base {
+struct IRAttribute : public IRPosition, public Base, public IRAttributeManifest {
+  ~IRAttribute() {}
 
   /// Constructors for the IRPosition.
   ///
@@ -666,7 +674,11 @@
   ///}
 
   /// See AbstractAttribute::manifest(...).
-  virtual ChangeStatus manifest(Attributor &A);
+  ChangeStatus manifest(Attributor &A) {
+    SmallVector<Attribute, 4> DeducedAttrs;
+    getDeducedAttributes(getAnchorScope().getContext(), DeducedAttrs);
+    return IRAttributeManifest::manifestAttrs(A, getIRPosition(), DeducedAttrs);
+  }
 
   /// Return the kind that identifies the abstract attribute implementation.
   Attribute::AttrKind getAttrKind() const { return AK; }
Index: llvm/include/llvm/module.modulemap
===================================================================
--- llvm/include/llvm/module.modulemap
+++ llvm/include/llvm/module.modulemap
@@ -333,11 +333,6 @@
   requires cplusplus
   umbrella "Transforms"
 
-  // FIXME: This is far from a perfect solution but at the moment this header
-  // is difficult to modularize and would require splitting it up. Exclude it
-  // completely to avoid a link failure with modular builds.
-  exclude header "Transforms/IPO/Attributor.h"
-
   module * { export * }
 }
 
Index: llvm/lib/Transforms/IPO/Attributor.cpp
===================================================================
--- llvm/lib/Transforms/IPO/Attributor.cpp
+++ llvm/lib/Transforms/IPO/Attributor.cpp
@@ -332,21 +332,16 @@
   return HasChanged;
 }
 
-template <Attribute::AttrKind AK, typename Base>
-ChangeStatus IRAttribute<AK, Base>::manifest(Attributor &A) {
-  assert(this->getState().isValidState() &&
-         "Attempted to manifest an invalid state!");
-  assert(getIRPosition().getAssociatedValue() &&
+ ChangeStatus IRAttributeManifest::manifestAttrs(Attributor &A, IRPosition
+     &IRP, const ArrayRef<Attribute> &DeducedAttrs) {
+  assert(IRP.getAssociatedValue() &&
          "Attempted to manifest an attribute without associated value!");
 
   ChangeStatus HasChanged = ChangeStatus::UNCHANGED;
 
-  Function &ScopeFn = getAnchorScope();
+  Function &ScopeFn = IRP.getAnchorScope();
   LLVMContext &Ctx = ScopeFn.getContext();
-  IRPosition::Kind PK = getPositionKind();
-
-  SmallVector<Attribute, 4> DeducedAttrs;
-  getDeducedAttributes(Ctx, DeducedAttrs);
+  IRPosition::Kind PK = IRP.getPositionKind();
 
   // In the following some generic code that will manifest attributes in
   // DeducedAttrs if they improve the current IR. Due to the different
@@ -360,12 +355,12 @@
     Attrs = ScopeFn.getAttributes();
     break;
   case IRPosition::IRP_CALL_SITE_ARGUMENT:
-    Attrs = ImmutableCallSite(&getAnchorValue()).getAttributes();
+    Attrs = ImmutableCallSite(&IRP.getAnchorValue()).getAttributes();
     break;
   }
 
   for (const Attribute &Attr : DeducedAttrs) {
-    if (!addIfNotExistent(Ctx, Attr, Attrs, getAttrIdx()))
+    if (!addIfNotExistent(Ctx, Attr, Attrs, IRP.getAttrIdx()))
       continue;
 
     HasChanged = ChangeStatus::CHANGED;
@@ -382,7 +377,7 @@
     ScopeFn.setAttributes(Attrs);
     break;
   case IRPosition::IRP_CALL_SITE_ARGUMENT:
-    CallSite(&getAnchorValue()).setAttributes(Attrs);
+    CallSite(&IRP.getAnchorValue()).setAttributes(Attrs);
   }
 
   return HasChanged;