1 files changed, 41 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/IVUsers.cpp b/llvm/lib/Analysis/IVUsers.cpp
index cad22f8f1a6..c598b72c0de 100644
--- a/llvm/lib/Analysis/IVUsers.cpp
+++ b/llvm/lib/Analysis/IVUsers.cpp
@@ -79,10 +79,30 @@ static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
   return false;
 }
 
+/// Return true if this loop and all loop headers that dominate it are in
+/// simplified form.
+static bool isSimplifiedLoopNest(Loop *L, const DominatorTree *DT,
+                                 const LoopInfo *LI) {
+  if (!L->isLoopSimplifyForm())
+    return false;
+
+  for (DomTreeNode *Rung = DT->getNode(L->getLoopPreheader());
+       Rung; Rung = Rung->getIDom()) {
+    BasicBlock *BB = Rung->getBlock();
+    const Loop *DomLoop = LI->getLoopFor(BB);
+    if (DomLoop && DomLoop->getHeader() == BB) {
+      if (!DomLoop->isLoopSimplifyForm())
+        return false;
+    }
+  }
+  return true;
+}
+
 /// AddUsersIfInteresting - Inspect the specified instruction.  If it is a
 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
 /// return true.  Otherwise, return false.
-bool IVUsers::AddUsersIfInteresting(Instruction *I) {
+bool IVUsers::AddUsersIfInteresting(Instruction *I,
+                                    SmallPtrSet<Loop*,16> &SimpleLoopNests) {
   // Add this IV user to the Processed set before returning false to ensure that
   // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
   if (!Processed.insert(I))
@@ -117,6 +137,16 @@ bool IVUsers::AddUsersIfInteresting(Instruction *I) {
     if (isa<PHINode>(User) && Processed.count(User))
       continue;
 
+    Loop *UserLoop = LI->getLoopFor(User->getParent());
+
+    // Only consider IVUsers that are dominated by simplified loop
+    // headers. Otherwise, SCEVExpander will crash.
+    if (UserLoop && !SimpleLoopNests.count(UserLoop)) {
+      if (!isSimplifiedLoopNest(UserLoop, DT, LI))
+        return false;
+      SimpleLoopNests.insert(UserLoop);
+    }
+
     // Descend recursively, but not into PHI nodes outside the current loop.
     // It's important to see the entire expression outside the loop to get
     // choices that depend on addressing mode use right, although we won't
@@ -124,14 +154,15 @@ bool IVUsers::AddUsersIfInteresting(Instruction *I) {
     // If User is already in Processed, we don't want to recurse into it again,
     // but do want to record a second reference in the same instruction.
     bool AddUserToIVUsers = false;
-    if (LI->getLoopFor(User->getParent()) != L) {
+    if (UserLoop != L) {
       if (isa<PHINode>(User) || Processed.count(User) ||
-          !AddUsersIfInteresting(User)) {
+          !AddUsersIfInteresting(User, SimpleLoopNests)) {
         DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
                      << "   OF SCEV: " << *ISE << '\n');
         AddUserToIVUsers = true;
       }
-    } else if (Processed.count(User) || !AddUsersIfInteresting(User)) {
+    } else if (Processed.count(User)
+               || !AddUsersIfInteresting(User, SimpleLoopNests)) {
       DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
                    << "   OF SCEV: " << *ISE << '\n');
       AddUserToIVUsers = true;
@@ -180,11 +211,16 @@ bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
   SE = &getAnalysis<ScalarEvolution>();
   TD = getAnalysisIfAvailable<TargetData>();
 
+  // SCEVExpander can only handle users that are dominated by simplified loop
+  // entries. Keep track of all loops that are only dominated by other simple
+  // loops so we don't traverse the domtree for each user.
+  SmallPtrSet<Loop*,16> SimpleLoopNests;
+
   // Find all uses of induction variables in this loop, and categorize
   // them by stride.  Start by finding all of the PHI nodes in the header for
   // this loop.  If they are induction variables, inspect their uses.
   for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
-    (void)AddUsersIfInteresting(I);
+    (void)AddUsersIfInteresting(I, SimpleLoopNests);
 
   return false;
 }