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

6 files changed, 115 insertions, 18 deletions

diff --git a/include/llvm/Analysis/IVUsers.h b/include/llvm/Analysis/IVUsers.h
index 2a3bb9bc48..11d2cf0ac7 100644
--- a/include/llvm/Analysis/IVUsers.h
+++ b/include/llvm/Analysis/IVUsers.h
@@ -145,7 +145,8 @@ public:
   /// 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 AddUsersIfInteresting(Instruction *I);
+  bool AddUsersIfInteresting(Instruction *I,
+                             SmallPtrSet<Loop*,16> &SimpleLoopNests);
 
   IVStrideUse &AddUser(Instruction *User, Value *Operand);
 
diff --git a/lib/Analysis/IVUsers.cpp b/lib/Analysis/IVUsers.cpp
index cad22f8f1a..c598b72c0d 100644
--- a/lib/Analysis/IVUsers.cpp
+++ b/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;
 }
diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index d1e57e101b..490617a0c8 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 6768860caa..82d918eeef 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);
diff --git a/lib/Transforms/Utils/SimplifyIndVar.cpp b/lib/Transforms/Utils/SimplifyIndVar.cpp
index 20eef3c0dc..e00565d5f9 100644
--- a/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -231,8 +231,10 @@ void SimplifyIndvar::eliminateIVRemainder(BinaryOperator *Rem,
 
   // Inform IVUsers about the new users.
   if (IU) {
-    if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0)))
-      IU->AddUsersIfInteresting(I);
+    if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0))) {
+      SmallPtrSet<Loop*, 16> SimplifiedLoopNests;
+      IU->AddUsersIfInteresting(I, SimplifiedLoopNests);
+    }
   }
   DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
   ++NumElimRem;
diff --git a/test/Transforms/LoopStrengthReduce/2012-03-15-nopreheader.ll b/test/Transforms/LoopStrengthReduce/2012-03-15-nopreheader.ll
new file mode 100644
index 0000000000..207e9d74f5
--- /dev/null
+++ b/test/Transforms/LoopStrengthReduce/2012-03-15-nopreheader.ll
@@ -0,0 +1,50 @@
+; RUN: opt -loop-reduce -S < %s | FileCheck %s
+;
+; <rdar://problem/11049788> Segmentation fault: 11 in LoopStrengthReduce
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-apple-darwin10.0.0"
+
+; IVUsers should not consider tmp128 a valid user because it is not in a
+; simplified loop nest.
+; CHECK: @nopreheader
+; CHECK: for.cond:
+; CHECK: %tmp128 = add i64 %0, %indvar65
+define void @nopreheader(i8* %cmd) nounwind ssp {
+entry:
+  indirectbr i8* undef, [label %while.cond]
+
+while.cond:                                       ; preds = %while.body, %entry
+  %0 = phi i64 [ %indvar.next48, %while.body ], [ 0, %entry ]
+  indirectbr i8* undef, [label %while.end, label %while.body]
+
+while.body:                                       ; preds = %lor.rhs, %lor.lhs.false17, %lor.lhs.false11, %lor.lhs.false, %land.rhs
+  %indvar.next48 = add i64 %0, 1
+  indirectbr i8* undef, [label %while.cond]
+
+while.end:                                        ; preds = %lor.rhs, %while.cond
+  indirectbr i8* undef, [label %if.end152]
+
+if.end152:                                        ; preds = %lor.lhs.false144, %if.end110
+  indirectbr i8* undef, [label %lor.lhs.false184, label %for.cond]
+
+lor.lhs.false184:                                 ; preds = %lor.lhs.false177
+  indirectbr i8* undef, [label %return, label %for.cond]
+
+for.cond:                                         ; preds = %for.inc, %lor.lhs.false184, %if.end152
+  %indvar65 = phi i64 [ %indvar.next66, %for.inc ], [ 0, %lor.lhs.false184 ], [ 0, %if.end152 ]
+  %tmp128 = add i64 %0, %indvar65
+  %s.4 = getelementptr i8* %cmd, i64 %tmp128
+  %tmp195 = load i8* %s.4, align 1
+  indirectbr i8* undef, [label %return, label %land.rhs198]
+
+land.rhs198:                                      ; preds = %for.cond
+  indirectbr i8* undef, [label %return, label %for.inc]
+
+for.inc:                                          ; preds = %lor.rhs234, %land.lhs.true228, %land.lhs.true216, %land.lhs.true204
+  %indvar.next66 = add i64 %indvar65, 1
+  indirectbr i8* undef, [label %for.cond]
+
+return:                                           ; preds = %if.end677, %doshell, %if.then96
+  ret void
+}