Index: llvm/trunk/lib/Analysis/MemorySSAUpdater.cpp
===================================================================
--- llvm/trunk/lib/Analysis/MemorySSAUpdater.cpp
+++ llvm/trunk/lib/Analysis/MemorySSAUpdater.cpp
@@ -313,10 +313,10 @@
   // and that def is now our defining access.
   MD->setDefiningAccess(DefBefore);
 
-  // Remember the index where we may insert new phis below.
-  unsigned NewPhiIndex = InsertedPHIs.size();
-
   SmallVector<WeakVH, 8> FixupList(InsertedPHIs.begin(), InsertedPHIs.end());
+
+  SmallPtrSet<BasicBlock *, 2> DefiningBlocks;
+
   if (!DefBeforeSameBlock) {
     // If there was a local def before us, we must have the same effect it
     // did. Because every may-def is the same, any phis/etc we would create, it
@@ -335,53 +335,49 @@
     auto Iter = MD->getDefsIterator();
     ++Iter;
     auto IterEnd = MSSA->getBlockDefs(MD->getBlock())->end();
-    if (Iter == IterEnd) {
-      ForwardIDFCalculator IDFs(*MSSA->DT);
-      SmallVector<BasicBlock *, 32> IDFBlocks;
-      SmallPtrSet<BasicBlock *, 2> DefiningBlocks;
-      for (const auto &VH : InsertedPHIs)
-        if (const auto *RealPHI = cast_or_null<MemoryPhi>(VH))
-          DefiningBlocks.insert(RealPHI->getBlock());
+    if (Iter == IterEnd)
       DefiningBlocks.insert(MD->getBlock());
-      IDFs.setDefiningBlocks(DefiningBlocks);
-      IDFs.calculate(IDFBlocks);
-      SmallVector<AssertingVH<MemoryPhi>, 4> NewInsertedPHIs;
-      for (auto *BBIDF : IDFBlocks) {
-        auto *MPhi = MSSA->getMemoryAccess(BBIDF);
-        if (!MPhi) {
-          MPhi = MSSA->createMemoryPhi(BBIDF);
-          NewInsertedPHIs.push_back(MPhi);
-        }
-        // Add the phis created into the IDF blocks to NonOptPhis, so they are
-        // not optimized out as trivial by the call to getPreviousDefFromEnd
-        // below. Once they are complete, all these Phis are added to the
-        // FixupList, and removed from NonOptPhis inside fixupDefs().
-        // Existing Phis in IDF may need fixing as well, and potentially be
-        // trivial before this insertion, hence add all IDF Phis. See PR43044.
-        NonOptPhis.insert(MPhi);
-      }
 
-      for (auto &MPhi : NewInsertedPHIs) {
-        auto *BBIDF = MPhi->getBlock();
-        for (auto *Pred : predecessors(BBIDF)) {
-          DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> CachedPreviousDef;
-          MPhi->addIncoming(getPreviousDefFromEnd(Pred, CachedPreviousDef),
-                            Pred);
-        }
-      }
+    FixupList.push_back(MD);
+  }
 
-      // Re-take the index where we're adding the new phis, because the above
-      // call to getPreviousDefFromEnd, may have inserted into InsertedPHIs.
-      NewPhiIndex = InsertedPHIs.size();
-      for (auto &MPhi : NewInsertedPHIs) {
-        InsertedPHIs.push_back(&*MPhi);
-        FixupList.push_back(&*MPhi);
-      }
+  ForwardIDFCalculator IDFs(*MSSA->DT);
+  SmallVector<BasicBlock *, 32> IDFBlocks;
+  for (const auto &VH : InsertedPHIs)
+    if (const auto *RealPHI = cast_or_null<MemoryPhi>(VH))
+      DefiningBlocks.insert(RealPHI->getBlock());
+  IDFs.setDefiningBlocks(DefiningBlocks);
+  IDFs.calculate(IDFBlocks);
+  SmallVector<AssertingVH<MemoryPhi>, 4> NewInsertedPHIs;
+  for (auto *BBIDF : IDFBlocks) {
+    auto *MPhi = MSSA->getMemoryAccess(BBIDF);
+    if (!MPhi) {
+      MPhi = MSSA->createMemoryPhi(BBIDF);
+      NewInsertedPHIs.push_back(MPhi);
+    }
+    // Add the phis created into the IDF blocks to NonOptPhis, so they are not
+    // optimized out as trivial by the call to getPreviousDefFromEnd below. Once
+    // they are complete, all these Phis are added to the FixupList, and removed
+    // from NonOptPhis inside fixupDefs(). Existing Phis in IDF may need fixing
+    // as well, and potentially be trivial before this insertion, hence add all
+    // IDF Phis. See PR43044.
+    NonOptPhis.insert(MPhi);
+  }
+
+  for (auto &MPhi : NewInsertedPHIs) {
+    auto *BBIDF = MPhi->getBlock();
+    for (auto *Pred : predecessors(BBIDF)) {
+      DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> CachedPreviousDef;
+      MPhi->addIncoming(getPreviousDefFromEnd(Pred, CachedPreviousDef), Pred);
     }
-
-    FixupList.push_back(MD);
   }
 
+  // Remember the index where we may insert new phis.
+  unsigned NewPhiIndex = InsertedPHIs.size();
+  for (auto &MPhi : NewInsertedPHIs) {
+    InsertedPHIs.push_back(&*MPhi);
+    FixupList.push_back(&*MPhi);
+  }
   // Remember the index where we stopped inserting new phis above, since the
   // fixupDefs call in the loop below may insert more, that are already minimal.
   unsigned NewPhiIndexEnd = InsertedPHIs.size();
Index: llvm/trunk/test/Analysis/MemorySSA/pr43317.ll
===================================================================
--- llvm/trunk/test/Analysis/MemorySSA/pr43317.ll
+++ llvm/trunk/test/Analysis/MemorySSA/pr43317.ll
@@ -0,0 +1,32 @@
+; RUN: opt -S -licm -enable-mssa-loop-dependency=true < %s | FileCheck %s
+; REQUIRES: asserts
+@v_274 = external dso_local global i64, align 1
+@v_295 = external dso_local global i16, align 1
+@v_335 = external dso_local global i32, align 1
+
+; CHECK-LABEL: @main()
+define dso_local void @main() {
+entry:
+  store i32 undef, i32* @v_335, align 1
+  br i1 undef, label %gate, label %exit
+
+nopredentry1:                                     ; No predecessors!
+  br label %preinfiniteloop
+
+nopredentry2:                                     ; No predecessors!
+  br label %gate
+
+gate:                                             ; preds = %nopredentry2, %entry
+  br i1 undef, label %preinfiniteloop, label %exit
+
+preinfiniteloop:                                  ; preds = %gate, %nopredentry1
+  br label %infiniteloop
+
+infiniteloop:                                     ; preds = %infiniteloop, %preinfiniteloop
+  store i16 undef, i16* @v_295, align 1
+  br label %infiniteloop
+
+exit:                                             ; preds = %gate, %entry
+  store i64 undef, i64* @v_274, align 1
+  ret void
+}