3 files changed, 36 insertions, 12 deletions

diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index d7661272899..408d1233412 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -782,8 +782,12 @@ namespace llvm {
         LoopDispositions;
 
     /// A cache of the predicate "does the given loop contain an instruction
-    /// that can throw?"
-    DenseMap<const Loop *, bool> LoopMayThrow;
+    /// that can abnormally exit the loop (i.e. via throwing an exception, by
+    /// terminating the thread cleanly or by infinite looping in a called
+    /// function)?"  The last one is strictly not leaving the loop, but is
+    /// identical to leaving the loop from the viewpoint of reasoning about
+    /// undefined behavior.
+    DenseMap<const Loop *, bool> LoopHasAbnormalExit;
 
     /// Compute a LoopDisposition value.
     LoopDisposition computeLoopDisposition(const SCEV *S, const Loop *L);
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 111b9b61d1e..2bd7e611917 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4909,19 +4909,19 @@ bool ScalarEvolution::isAddRecNeverPoison(const Instruction *I, const Loop *L) {
   if (!LatchControlDependentOnPoison)
     return false;
 
-  // Now check if loop is no-throw, and cache the information.  In the future,
-  // we can consider commoning this logic with LICMSafetyInfo into a separate
-  // analysis pass.
+  // Now check if loop has abonormal exits (or not), and cache the information.
 
-  auto Itr = LoopMayThrow.find(L);
-  if (Itr == LoopMayThrow.end()) {
-    bool MayThrow = false;
+  auto Itr = LoopHasAbnormalExit.find(L);
+  if (Itr == LoopHasAbnormalExit.end()) {
+    bool HasAbnormalExit = false;
     for (auto *BB : L->getBlocks()) {
-      MayThrow = any_of(*BB, [](Instruction &I) { return I.mayThrow(); });
-      if (MayThrow)
+      HasAbnormalExit = any_of(*BB, [](Instruction &I) {
+        return !isGuaranteedToTransferExecutionToSuccessor(&I);
+      });
+      if (HasAbnormalExit)
         break;
     }
-    auto InsertPair = LoopMayThrow.insert({L, MayThrow});
+    auto InsertPair = LoopHasAbnormalExit.insert({L, HasAbnormalExit});
     assert(InsertPair.second && "We just checked!");
     Itr = InsertPair.first;
   }
@@ -5490,7 +5490,7 @@ void ScalarEvolution::forgetLoop(const Loop *L) {
   for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
     forgetLoop(*I);
 
-  LoopMayThrow.erase(L);
+  LoopHasAbnormalExit.erase(L);
 }
 
 void ScalarEvolution::forgetValue(Value *V) {
diff --git a/llvm/test/Analysis/ScalarEvolution/nsw.ll b/llvm/test/Analysis/ScalarEvolution/nsw.ll
index e89973be2b0..49050c53d06 100644
--- a/llvm/test/Analysis/ScalarEvolution/nsw.ll
+++ b/llvm/test/Analysis/ScalarEvolution/nsw.ll
@@ -240,3 +240,23 @@ loop:
 leave:
   ret void
 }
+
+declare void @may_exit() nounwind
+
+define void @pr28012(i32 %n) {
+; CHECK-LABEL: Classifying expressions for: @pr28012
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ 0, %entry ], [ %iv.inc, %loop ]
+  %iv.inc = add nsw i32 %iv, 7
+; CHECK:    %iv.inc = add nsw i32 %iv, 7
+; CHECK-NEXT:  -->  {7,+,7}<nuw><%loop>
+  %becond = icmp ult i32 %iv.inc, %n
+  call void @may_exit()
+  br i1 %becond, label %loop, label %leave
+
+leave:
+  ret void
+}