1 files changed, 14 insertions, 37 deletions

diff --git a/llvm/lib/Transforms/Scalar/ADCE.cpp b/llvm/lib/Transforms/Scalar/ADCE.cpp
index 571e70c746e..63205461c08 100644
--- a/llvm/lib/Transforms/Scalar/ADCE.cpp
+++ b/llvm/lib/Transforms/Scalar/ADCE.cpp
@@ -253,46 +253,23 @@ void AggressiveDeadCodeElimination::initialize() {
     }
   }
 
-  // Mark blocks live if there is no path from the block to the
-  // return of the function or a successor for which this is true.
-  // This protects IDFCalculator which cannot handle such blocks.
-  for (auto &BBInfoPair : BlockInfo) {
-    auto &BBInfo = BBInfoPair.second;
-    if (BBInfo.terminatorIsLive())
-      continue;
-    auto *BB = BBInfo.BB;
-    if (!PDT.getNode(BB)) {
-      markLive(BBInfo.Terminator);
-      continue;
-    }
-    for (auto *Succ : successors(BB))
-      if (!PDT.getNode(Succ)) {
-        markLive(BBInfo.Terminator);
-        break;
-      }
-  }
-
-  // Mark blocks live if there is no path from the block to the
-  // return of the function or a successor for which this is true.
-  // This protects IDFCalculator which cannot handle such blocks.
-  for (auto &BBInfoPair : BlockInfo) {
-    auto &BBInfo = BBInfoPair.second;
-    if (BBInfo.terminatorIsLive())
-      continue;
-    auto *BB = BBInfo.BB;
-    if (!PDT.getNode(BB)) {
-      DEBUG(dbgs() << "Not post-dominated by return: " << BB->getName()
+  // Mark blocks live if there is no path from the block to a
+  // return of the function.
+  // We do this by seeing which of the postdomtree root children exit the
+  // program, and for all others, mark the subtree live.
+  for (auto &PDTChild : children<DomTreeNode *>(PDT.getRootNode())) {
+    auto *BB = PDTChild->getBlock();
+    auto &Info = BlockInfo[BB];
+    // Real function return
+    if (isa<ReturnInst>(Info.Terminator)) {
+      DEBUG(dbgs() << "post-dom root child is not a return: " << BB->getName()
                    << '\n';);
-      markLive(BBInfo.Terminator);
       continue;
     }
-    for (auto *Succ : successors(BB))
-      if (!PDT.getNode(Succ)) {
-        DEBUG(dbgs() << "Successor not post-dominated by return: "
-                     << BB->getName() << '\n';);
-        markLive(BBInfo.Terminator);
-        break;
-      }
+
+    // This child is something else, like an infinite loop.
+    for (auto DFNode : depth_first(PDTChild))
+      markLive(BlockInfo[DFNode->getBlock()].Terminator);
   }
 
   // Treat the entry block as always live