1 files changed, 98 insertions, 57 deletions

diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index 0fb6798..09d569a 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -73,6 +73,7 @@ namespace {
     LoopInfo        *LI;
     ScalarEvolution *SE;
     DominatorTree   *DT;
+    SmallVector<WeakVH, 16> DeadInsts;
     bool Changed;
   public:
 
@@ -98,6 +99,7 @@ namespace {
     }
 
   private:
+    bool isValidRewrite(Value *FromVal, Value *ToVal);
 
     void EliminateIVComparisons();
     void EliminateIVRemainders();
@@ -134,6 +136,53 @@ Pass *llvm::createIndVarSimplifyPass() {
   return new IndVarSimplify();
 }
 
+/// isValidRewrite - Return true if the SCEV expansion generated by the
+/// rewriter can replace the original value. SCEV guarantees that it
+/// produces the same value, but the way it is produced may be illegal IR.
+/// Ideally, this function will only be called for verification.
+bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) {
+  // If an SCEV expression subsumed multiple pointers, its expansion could
+  // reassociate the GEP changing the base pointer. This is illegal because the
+  // final address produced by a GEP chain must be inbounds relative to its
+  // underlying object. Otherwise basic alias analysis, among other things,
+  // could fail in a dangerous way. Ultimately, SCEV will be improved to avoid
+  // producing an expression involving multiple pointers. Until then, we must
+  // bail out here.
+  //
+  // Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject
+  // because it understands lcssa phis while SCEV does not.
+  Value *FromPtr = FromVal;
+  Value *ToPtr = ToVal;
+  if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) {
+    FromPtr = GEP->getPointerOperand();
+  }
+  if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) {
+    ToPtr = GEP->getPointerOperand();
+  }
+  if (FromPtr != FromVal || ToPtr != ToVal) {
+    // Quickly check the common case
+    if (FromPtr == ToPtr)
+      return true;
+
+    // SCEV may have rewritten an expression that produces the GEP's pointer
+    // operand. That's ok as long as the pointer operand has the same base
+    // pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the
+    // base of a recurrence. This handles the case in which SCEV expansion
+    // converts a pointer type recurrence into a nonrecurrent pointer base
+    // indexed by an integer recurrence.
+    const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr));
+    const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr));
+    if (FromBase == ToBase)
+      return true;
+
+    DEBUG(dbgs() << "INDVARS: GEP rewrite bail out "
+          << *FromBase << " != " << *ToBase << "\n");
+
+    return false;
+  }
+  return true;
+}
+
 /// LinearFunctionTestReplace - This method rewrites the exit condition of the
 /// loop to be a canonical != comparison against the incremented loop induction
 /// variable.  This pass is able to rewrite the exit tests of any loop where the
@@ -226,7 +275,7 @@ ICmpInst *IndVarSimplify::LinearFunctionTestReplace(Loop *L,
   // update the branch to use the new comparison; in the common case this
   // will make old comparison dead.
   BI->setCondition(Cond);
-  RecursivelyDeleteTriviallyDeadInstructions(OrigCond);
+  DeadInsts.push_back(OrigCond);
 
   ++NumLFTR;
   Changed = true;
@@ -304,14 +353,18 @@ void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
         if (!SE->isLoopInvariant(ExitValue, L))
           continue;
 
-        Changed = true;
-        ++NumReplaced;
-
         Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
 
         DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
                      << "  LoopVal = " << *Inst << "\n");
 
+        if (!isValidRewrite(Inst, ExitVal)) {
+          DeadInsts.push_back(ExitVal);
+          continue;
+        }
+        Changed = true;
+        ++NumReplaced;
+
         PN->setIncomingValue(i, ExitVal);
 
         // If this instruction is dead now, delete it.
@@ -366,8 +419,6 @@ void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
 }
 
 void IndVarSimplify::EliminateIVComparisons() {
-  SmallVector<WeakVH, 16> DeadInsts;
-
   // Look for ICmp users.
   for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
     IVStrideUse &UI = *I;
@@ -399,18 +450,9 @@ void IndVarSimplify::EliminateIVComparisons() {
     DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
     DeadInsts.push_back(ICmp);
   }
-
-  // Now that we're done iterating through lists, clean up any instructions
-  // which are now dead.
-  while (!DeadInsts.empty())
-    if (Instruction *Inst =
-        dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
-      RecursivelyDeleteTriviallyDeadInstructions(Inst);
 }
 
 void IndVarSimplify::EliminateIVRemainders() {
-  SmallVector<WeakVH, 16> DeadInsts;
-
   // Look for SRem and URem users.
   for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
     IVStrideUse &UI = *I;
@@ -466,13 +508,6 @@ void IndVarSimplify::EliminateIVRemainders() {
     DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
     DeadInsts.push_back(Rem);
   }
-
-  // Now that we're done iterating through lists, clean up any instructions
-  // which are now dead.
-  while (!DeadInsts.empty())
-    if (Instruction *Inst =
-          dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
-      RecursivelyDeleteTriviallyDeadInstructions(Inst);
 }
 
 bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
@@ -491,6 +526,7 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
   LI = &getAnalysis<LoopInfo>();
   SE = &getAnalysis<ScalarEvolution>();
   DT = &getAnalysis<DominatorTree>();
+  DeadInsts.clear();
   Changed = false;
 
   // If there are any floating-point recurrences, attempt to
@@ -589,9 +625,21 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
                                           ExitingBlock, BI, Rewriter);
   }
 
-  // Rewrite IV-derived expressions. Clears the rewriter cache.
+  // Rewrite IV-derived expressions.
   RewriteIVExpressions(L, Rewriter);
 
+  // Clear the rewriter cache, because values that are in the rewriter's cache
+  // can be deleted in the loop below, causing the AssertingVH in the cache to
+  // trigger.
+  Rewriter.clear();
+
+  // Now that we're done iterating through lists, clean up any instructions
+  // which are now dead.
+  while (!DeadInsts.empty())
+    if (Instruction *Inst =
+          dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
+      RecursivelyDeleteTriviallyDeadInstructions(Inst);
+
   // The Rewriter may not be used from this point on.
 
   // Loop-invariant instructions in the preheader that aren't used in the
@@ -632,7 +680,7 @@ static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) {
       if (!isSafe(*I, L, SE)) return false;
     return true;
   }
-  
+
   // A cast is safe if its operand is.
   if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S))
     return isSafe(C->getOperand(), L, SE);
@@ -651,8 +699,6 @@ static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) {
 }
 
 void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
-  SmallVector<WeakVH, 16> DeadInsts;
-
   // Rewrite all induction variable expressions in terms of the canonical
   // induction variable.
   //
@@ -705,6 +751,13 @@ void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
     // Now expand it into actual Instructions and patch it into place.
     Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt);
 
+    DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n'
+                 << "   into = " << *NewVal << "\n");
+
+    if (!isValidRewrite(Op, NewVal)) {
+      DeadInsts.push_back(NewVal);
+      continue;
+    }
     // Inform ScalarEvolution that this value is changing. The change doesn't
     // affect its value, but it does potentially affect which use lists the
     // value will be on after the replacement, which affects ScalarEvolution's
@@ -717,25 +770,13 @@ void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
       NewVal->takeName(Op);
     User->replaceUsesOfWith(Op, NewVal);
     UI->setOperandValToReplace(NewVal);
-    DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n'
-                 << "   into = " << *NewVal << "\n");
+
     ++NumRemoved;
     Changed = true;
 
     // The old value may be dead now.
     DeadInsts.push_back(Op);
   }
-
-  // Clear the rewriter cache, because values that are in the rewriter's cache
-  // can be deleted in the loop below, causing the AssertingVH in the cache to
-  // trigger.
-  Rewriter.clear();
-  // Now that we're done iterating through lists, clean up any instructions
-  // which are now dead.
-  while (!DeadInsts.empty())
-    if (Instruction *Inst =
-          dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
-      RecursivelyDeleteTriviallyDeadInstructions(Inst);
 }
 
 /// If there's a single exit block, sink any loop-invariant values that
@@ -859,7 +900,7 @@ void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
   BinaryOperator *Incr =
     dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge));
   if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return;
-  
+
   // If this is not an add of the PHI with a constantfp, or if the constant fp
   // is not an integer, bail out.
   ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
@@ -884,7 +925,7 @@ void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
   if (Compare == 0 || !Compare->hasOneUse() ||
       !isa<BranchInst>(Compare->use_back()))
     return;
-  
+
   BranchInst *TheBr = cast<BranchInst>(Compare->use_back());
 
   // We need to verify that the branch actually controls the iteration count
@@ -896,8 +937,8 @@ void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
       (L->contains(TheBr->getSuccessor(0)) &&
        L->contains(TheBr->getSuccessor(1))))
     return;
-  
-  
+
+
   // If it isn't a comparison with an integer-as-fp (the exit value), we can't
   // transform it.
   ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
@@ -905,7 +946,7 @@ void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
   if (ExitValueVal == 0 ||
       !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
     return;
-  
+
   // Find new predicate for integer comparison.
   CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
   switch (Compare->getPredicate()) {
@@ -923,13 +964,13 @@ void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
   case CmpInst::FCMP_OLE:
   case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
   }
-  
+
   // We convert the floating point induction variable to a signed i32 value if
   // we can.  This is only safe if the comparison will not overflow in a way
   // that won't be trapped by the integer equivalent operations.  Check for this
   // now.
   // TODO: We could use i64 if it is native and the range requires it.
-  
+
   // The start/stride/exit values must all fit in signed i32.
   if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue))
     return;
@@ -945,59 +986,59 @@ void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
     if (InitValue >= ExitValue ||
         NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE)
       return;
-    
+
     uint32_t Range = uint32_t(ExitValue-InitValue);
     if (NewPred == CmpInst::ICMP_SLE) {
       // Normalize SLE -> SLT, check for infinite loop.
       if (++Range == 0) return;  // Range overflows.
     }
-    
+
     unsigned Leftover = Range % uint32_t(IncValue);
-    
+
     // If this is an equality comparison, we require that the strided value
     // exactly land on the exit value, otherwise the IV condition will wrap
     // around and do things the fp IV wouldn't.
     if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
         Leftover != 0)
       return;
-    
+
     // If the stride would wrap around the i32 before exiting, we can't
     // transform the IV.
     if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue)
       return;
-    
+
   } else {
     // If we have a negative stride, we require the init to be greater than the
     // exit value and an equality or greater than comparison.
     if (InitValue >= ExitValue ||
         NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE)
       return;
-    
+
     uint32_t Range = uint32_t(InitValue-ExitValue);
     if (NewPred == CmpInst::ICMP_SGE) {
       // Normalize SGE -> SGT, check for infinite loop.
       if (++Range == 0) return;  // Range overflows.
     }
-    
+
     unsigned Leftover = Range % uint32_t(-IncValue);
-    
+
     // If this is an equality comparison, we require that the strided value
     // exactly land on the exit value, otherwise the IV condition will wrap
     // around and do things the fp IV wouldn't.
     if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
         Leftover != 0)
       return;
-    
+
     // If the stride would wrap around the i32 before exiting, we can't
     // transform the IV.
     if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue)
       return;
   }
-  
+
   const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
 
   // Insert new integer induction variable.
-  PHINode *NewPHI = PHINode::Create(Int32Ty, PN->getName()+".int", PN);
+  PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN);
   NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
                       PN->getIncomingBlock(IncomingEdge));