[Attributor] FIX: Treat new attributes as changed ones

[jdoerfert]

Summary

When we have new attributes and we end the fixpoint iteration because
the iteration limit is reached, we need to treat the new ones as if they
changed in the last iteration, as they might have.

This adds a test for which we should not derive anything regardless of
the iteration limit, e.g., if we abort there should not be any
attributes manifested in the IR.

[sstefan1]

LGTM

llvm/lib/Transforms/IPO/Attributor.cpp

do {
 
     // Update all abstract attribute in the work list and record the ones that
     // changed.
     for (AbstractAttribute *AA : Worklist)
       if (!isAssumedDead(*AA, nullptr))
         if (AA->update(*this) == ChangeStatus::CHANGED)
           ChangedAAs.push_back(AA);
 
+    // Add attributes to the changed set if they have been created in the last
+    // iteration.
+    ChangedAAs.append(AllAbstractAttributes.begin() + NumAAs,
+                      AllAbstractAttributes.end());
+
     // Reset the work list and repopulate with the changed abstract attributes.
     // Note that dependent ones are added above.
     Worklist.clear();
     Worklist.insert(ChangedAAs.begin(), ChangedAAs.end());
 
-    // Add attributes to the worklist that have been created in the last
-    // iteration.
-    Worklist.insert(AllAbstractAttributes.begin() + NumAAs,
-                    AllAbstractAttributes.end());
-
   } while (!Worklist.empty() && ++IterationCounter < MaxFixpointIterations);
 
   size_t NumFinalAAs = AllAbstractAttributes.size();
 
   LLVM_DEBUG(dbgs() << "\n[Attributor] Fixpoint iteration done after: "
                     << IterationCounter << "/" << MaxFixpointIterations
                     << " iterations\n");
 

llvm/test/Transforms/FunctionAttrs/new_attributes.ll

+; RUN: opt < %s -attributor -attributor-disable=false -attributor-max-iterations=0 -S | FileCheck %s
+; RUN: opt < %s -attributor -attributor-disable=false -attributor-max-iterations=1 -S | FileCheck %s
+; RUN: opt < %s -attributor -attributor-disable=false -attributor-max-iterations=2 -S | FileCheck %s
+; RUN: opt < %s -attributor -attributor-disable=false -attributor-max-iterations=3 -S | FileCheck %s
+; RUN: opt < %s -attributor -attributor-disable=false -attributor-max-iterations=4 -S | FileCheck %s
+; RUN: opt < %s -attributor -attributor-disable=false -attributor-max-iterations=2147483647 -S | FileCheck %s
+
+; CHECK-NOT: Function
+; CHECK: declare i32 @foo1()
+; CHECK-NOT: Function
+; CHECK: declare i32 @foo2()
+; CHECK-NOT: Function
+; CHECK: declare i32 @foo3()
+declare i32 @foo1()
+declare i32 @foo2()
+declare i32 @foo3()
+
+; CHECK-NOT: Function
+; CHECK:      define internal i32 @bar() {
+; CHECK-NEXT:   %1 = call i32 @foo1()
+; CHECK-NEXT:   %2 = call i32 @foo2()
+; CHECK-NEXT:   %3 = call i32 @foo3()
+; CHECK-NEXT:   ret i32 1
+; CHECK-NEXT: }
+define internal i32 @bar() {
+  %1 = call i32 @foo1()
+  %2 = call i32 @foo2()
+  %3 = call i32 @foo3()
+  ret i32 1
+}
+
+; CHECK-NOT: Function
+; CHECK:      define i32 @baz() {
+; CHECK-NEXT:   %1 = call i32 @bar()
+; CHECK-NEXT:   ret i32 0
+; CHECK-NEXT: }
+define i32 @baz() {
+  %1 = call i32 @bar()
+  ret i32 0
+}
+
+; We should never derive anything here
+; CHECK-NOT: attributes