LSR fix: Add isSimplifiedLoopNest to IVUsers analysis.

Only record IVUsers that are dominated by simplified loop
headers. Otherwise SCEVExpander will crash while looking for a
preheader.

I previously tried to work around this in LSR itself, but that was
insufficient. This way, LSR can continue to run if some uses are not
in simple loops, as long as we don't attempt to analyze those users.

Fixes <rdar://problem/11049788> Segmentation fault: 11 in LoopStrengthReduce

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152892 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 18 insertions, 10 deletions

diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index d1e57e1..490617a 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -450,8 +450,10 @@ void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
   }
 
   // Add a new IVUsers entry for the newly-created integer PHI.
-  if (IU)
-    IU->AddUsersIfInteresting(NewPHI);
+  if (IU) {
+    SmallPtrSet<Loop*, 16> SimplifiedLoopNests;
+    IU->AddUsersIfInteresting(NewPHI, SimplifiedLoopNests);
+  }
 
   Changed = true;
 }
@@ -1967,8 +1969,11 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
   // loop exit test instruction.
   if (IU && NewICmp) {
     ICmpInst *NewICmpInst = dyn_cast<ICmpInst>(NewICmp);
-    if (NewICmpInst)
-      IU->AddUsersIfInteresting(cast<Instruction>(NewICmpInst->getOperand(0)));
+    if (NewICmpInst) {
+      SmallPtrSet<Loop*, 16> SimplifiedLoopNests;
+      IU->AddUsersIfInteresting(cast<Instruction>(NewICmpInst->getOperand(0)),
+                                SimplifiedLoopNests);
+    }
   }
   // Clean up dead instructions.
   Changed |= DeleteDeadPHIs(L->getHeader());
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 6768860..82d918e 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -4534,22 +4534,25 @@ LSRInstance::LSRInstance(const TargetLowering *tli, Loop *l, Pass *P)
   if (!L->isLoopSimplifyForm())
     return;
 
+  // If there's no interesting work to be done, bail early.
+  if (IU.empty()) return;
+
+#ifndef NDEBUG
   // All dominating loops must have preheaders, or SCEVExpander may not be able
   // to materialize an AddRecExpr whose Start is an outer AddRecExpr.
   //
-  // FIXME: This is a little absurd. I think LoopSimplify should be taught
-  // to create a preheader under any circumstance.
+  // IVUsers analysis should only create users that are dominated by simple loop
+  // headers. Since this loop should dominate all of its users, its user list
+  // should be empty if this loop itself is not within a simple loop nest.
   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->getLoopPreheader())
-        return;
+      assert(DomLoop->getLoopPreheader() && "LSR needs a simplified loop nest");
     }
   }
-  // If there's no interesting work to be done, bail early.
-  if (IU.empty()) return;
+#endif // DEBUG
 
   DEBUG(dbgs() << "\nLSR on loop ";
         WriteAsOperand(dbgs(), L->getHeader(), /*PrintType=*/false);