1 files changed, 24 insertions, 4 deletions
diff --git a/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
index 28f88f39a712d..a8445e94e55a0 100644
--- a/llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
@@ -230,6 +230,27 @@ static Loop *separateNestedLoop(Loop *L, BasicBlock *Preheader,
   if (!Preheader)
     return nullptr;
 
+  // Treat the presence of convergent functions conservatively. The
+  // transformation is invalid if calls to certain convergent
+  // functions (like an AMDGPU barrier) get included in the resulting
+  // inner loop. But blocks meant for the inner loop will be
+  // identified later at a point where it's too late to abort the
+  // transformation. Also, the convergent attribute is not really
+  // sufficient to express the semantics of functions that are
+  // affected by this transformation. So we choose to back off if such
+  // a function call is present until a better alternative becomes
+  // available. This is similar to the conservative treatment of
+  // convergent function calls in GVNHoist and JumpThreading.
+  for (auto BB : L->blocks()) {
+    for (auto &II : *BB) {
+      if (auto CI = dyn_cast<CallBase>(&II)) {
+        if (CI->isConvergent()) {
+          return nullptr;
+        }
+      }
+    }
+  }
+
   // The header is not a landing pad; preheader insertion should ensure this.
   BasicBlock *Header = L->getHeader();
   assert(!Header->isEHPad() && "Can't insert backedge to EH pad");
@@ -598,6 +619,7 @@ ReprocessLoop:
       if (!PreserveLCSSA || LI->replacementPreservesLCSSAForm(PN, V)) {
         PN->replaceAllUsesWith(V);
         PN->eraseFromParent();
+        Changed = true;
       }
     }
 
@@ -674,10 +696,8 @@ ReprocessLoop:
       LI->removeBlock(ExitingBlock);
 
       DomTreeNode *Node = DT->getNode(ExitingBlock);
-      const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
-        Node->getChildren();
-      while (!Children.empty()) {
-        DomTreeNode *Child = Children.front();
+      while (!Node->isLeaf()) {
+        DomTreeNode *Child = Node->back();
         DT->changeImmediateDominator(Child, Node->getIDom());
       }
       DT->eraseNode(ExitingBlock);