Index: llvm/include/llvm/Transforms/IPO/Attributor.h
===================================================================
--- llvm/include/llvm/Transforms/IPO/Attributor.h
+++ llvm/include/llvm/Transforms/IPO/Attributor.h
@@ -103,6 +103,7 @@
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/CGSCCPassManager.h"
 #include "llvm/Analysis/CallGraph.h"
+#include "llvm/Analysis/InlineCost.h"
 #include "llvm/Analysis/LazyCallGraph.h"
 #include "llvm/Analysis/MustExecute.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
@@ -1704,7 +1705,7 @@
     }
 
     bool IsFnInterface = IRP.isFnInterfaceKind();
-    const Function *FnScope = IRP.getAnchorScope();
+    Function *FnScope = IRP.getAnchorScope();
     // TODO: Not all attributes require an exact definition. Find a way to
     //       enable deduction for some but not all attributes in case the
     //       definition might be changed at runtime, see also
@@ -1712,8 +1713,15 @@
     // TODO: We could always determine abstract attributes and if sufficient
     //       information was found we could duplicate the functions that do not
     //       have an exact definition.
-    if (IsFnInterface && (!FnScope || !FnScope->hasExactDefinition()))
+    if (IsFnInterface && (!FnScope || !FnScope->hasExactDefinition())) {
+      if (FnScope->hasFnAttribute(Attribute::AlwaysInline)) {
+        // check if it is OK to inline, if so, do fix-point analysis for the
+        // function
+        if (isInlineViable(*FnScope).isSuccess())
+          return;
+      }
       this->getState().indicatePessimisticFixpoint();
+    }
   }
 
   /// See AbstractAttribute::manifest(...).
@@ -2748,7 +2756,8 @@
   /// Return an assumed constant for the assocaited value a program point \p
   /// CtxI.
   Optional<ConstantInt *>
-  getAssumedConstantInt(Attributor &A, const Instruction *CtxI = nullptr) const {
+  getAssumedConstantInt(Attributor &A,
+                        const Instruction *CtxI = nullptr) const {
     ConstantRange RangeV = getAssumedConstantRange(A, CtxI);
     if (auto *C = RangeV.getSingleElement())
       return cast<ConstantInt>(
Index: llvm/test/Transforms/Attributor/alwaysinline.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/Attributor/alwaysinline.ll
@@ -0,0 +1,78 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -attributor -attributor-disable=false -attributor-annotate-decl-cs -attributor-max-iterations=5 -S < %s | FileCheck %s --check-prefix=ATTRIBUTOR
+;
+; When a function is marked `alwaysinline` and is able to be inlined,
+; we can IPO its boundaries
+
+; The function can be removed safely because it has external linkage
+; so this will be inlined, although the function is not exactly
+; defined.
+; ATTRIBUTOR: Function Attrs: alwaysinline nofree nosync nounwind readnone
+define linkonce void @inner1() alwaysinline {
+; ATTRIBUTOR-LABEL: @inner1(
+; ATTRIBUTOR-NEXT:  entry:
+; ATTRIBUTOR-NEXT:    ret void
+;
+entry:
+  ret void
+}
+
+; ATTRIBUTOR: Function Attrs: nofree nosync nounwind
+define void @outer1() {
+; ATTRIBUTOR-LABEL: @outer1(
+; ATTRIBUTOR-NEXT:  entry:
+; ATTRIBUTOR-NEXT:    ret void
+;
+entry:
+  call void @inner1()
+  ret void
+}
+
+; The function is not alwaysinline and is external
+define i32 @inner2() {
+; ATTRIBUTOR-LABEL: @inner2(
+; ATTRIBUTOR-NEXT:  entry:
+; ATTRIBUTOR-NEXT:    ret i32 1
+;
+entry:
+  ret i32 1
+}
+
+define i32 @outer2() {
+; ATTRIBUTOR-LABEL: @outer2(
+; ATTRIBUTOR-NEXT:  entry:
+; ATTRIBUTOR-NEXT:    ret i32 1
+;
+entry:
+  %r = call i32 @inner2() alwaysinline
+  ret i32 %r
+}
+
+; This function cannot be inlined although it is marked alwaysinline
+declare i32 @a() returns_twice
+
+define internal i32 @inner3() alwaysinline {
+; ATTRIBUTOR-LABEL: @inner3(
+; ATTRIBUTOR-NEXT:  entry:
+; ATTRIBUTOR-NEXT:    [[CALL:%.*]] = call i32 @a() #3
+; ATTRIBUTOR-NEXT:    [[ADD:%.*]] = add nsw i32 1, [[CALL]]
+; ATTRIBUTOR-NEXT:    ret i32 [[ADD]]
+;
+entry:
+  %call = call i32 @a() returns_twice
+  %add = add nsw i32 1, %call
+  ret i32 %add
+}
+
+define i32 @outer3() {
+; ATTRIBUTOR-LABEL: @outer3(
+; ATTRIBUTOR-NEXT:  entry:
+; ATTRIBUTOR-NEXT:    [[CALL:%.*]] = call i32 @inner3()
+; ATTRIBUTOR-NEXT:    [[ADD:%.*]] = add nsw i32 1, [[CALL]]
+; ATTRIBUTOR-NEXT:    ret i32 [[ADD]]
+;
+entry:
+  %call = call i32 @inner3()
+  %add = add nsw i32 1, %call
+  ret i32 %add
+}