2 files changed, 44 insertions, 9 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 59e76c0538f..4e0dba7e04b 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -66,6 +66,7 @@
 #include "llvm/GlobalVariable.h"
 #include "llvm/Instructions.h"
 #include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/Dominators.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Assembly/Writer.h"
 #include "llvm/Transforms/Scalar.h"
@@ -205,6 +206,10 @@ SCEVTruncateExpr::~SCEVTruncateExpr() {
   SCEVTruncates->erase(std::make_pair(Op, Ty));
 }
 
+bool SCEVTruncateExpr::dominates(BasicBlock *BB, DominatorTree *DT) const {
+  return Op->dominates(BB, DT);
+}
+
 void SCEVTruncateExpr::print(std::ostream &OS) const {
   OS << "(truncate " << *Op << " to " << *Ty << ")";
 }
@@ -227,6 +232,10 @@ SCEVZeroExtendExpr::~SCEVZeroExtendExpr() {
   SCEVZeroExtends->erase(std::make_pair(Op, Ty));
 }
 
+bool SCEVZeroExtendExpr::dominates(BasicBlock *BB, DominatorTree *DT) const {
+  return Op->dominates(BB, DT);
+}
+
 void SCEVZeroExtendExpr::print(std::ostream &OS) const {
   OS << "(zeroextend " << *Op << " to " << *Ty << ")";
 }
@@ -249,6 +258,10 @@ SCEVSignExtendExpr::~SCEVSignExtendExpr() {
   SCEVSignExtends->erase(std::make_pair(Op, Ty));
 }
 
+bool SCEVSignExtendExpr::dominates(BasicBlock *BB, DominatorTree *DT) const {
+  return Op->dominates(BB, DT);
+}
+
 void SCEVSignExtendExpr::print(std::ostream &OS) const {
   OS << "(signextend " << *Op << " to " << *Ty << ")";
 }
@@ -306,6 +319,14 @@ replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
   return this;
 }
 
+bool SCEVCommutativeExpr::dominates(BasicBlock *BB, DominatorTree *DT) const {
+  for (unsigned i = 0, e = getNumOperands(); i != e; ++i) {
+    if (!getOperand(i)->dominates(BB, DT))
+      return false;
+  }
+  return true;
+}
+
 
 // SCEVUDivs - Only allow the creation of one SCEVUDivExpr for any particular
 // input.  Don't use a SCEVHandle here, or else the object will never be
@@ -317,6 +338,10 @@ SCEVUDivExpr::~SCEVUDivExpr() {
   SCEVUDivs->erase(std::make_pair(LHS, RHS));
 }
 
+bool SCEVUDivExpr::dominates(BasicBlock *BB, DominatorTree *DT) const {
+  return LHS->dominates(BB, DT) && RHS->dominates(BB, DT);
+}
+
 void SCEVUDivExpr::print(std::ostream &OS) const {
   OS << "(" << *LHS << " /u " << *RHS << ")";
 }
@@ -337,6 +362,15 @@ SCEVAddRecExpr::~SCEVAddRecExpr() {
                                                            Operands.end())));
 }
 
+bool SCEVAddRecExpr::dominates(BasicBlock *BB, DominatorTree *DT) const {
+  for (unsigned i = 0, e = getNumOperands(); i != e; ++i) {
+    if (!getOperand(i)->dominates(BB, DT))
+      return false;
+  }
+  return true;
+}
+
+
 SCEVHandle SCEVAddRecExpr::
 replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
                                   const SCEVHandle &Conc,
@@ -391,6 +425,12 @@ bool SCEVUnknown::isLoopInvariant(const Loop *L) const {
   return true;
 }
 
+bool SCEVUnknown::dominates(BasicBlock *BB, DominatorTree *DT) const {
+  if (Instruction *I = dyn_cast<Instruction>(getValue()))
+    return DT->dominates(I->getParent(), BB);
+  return true;
+}
+
 const Type *SCEVUnknown::getType() const {
   return V->getType();
 }
diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 055114c215d..0945a5759f8 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -438,16 +438,11 @@ static bool getSCEVStartAndStride(const SCEVHandle &SH, Loop *L,
   Start = SE->getAddExpr(Start, AddRec->getOperand(0));
   
   if (!isa<SCEVConstant>(AddRec->getOperand(1))) {
-    // If stride is an instruction, make sure it dominates the loop header.
+    // If stride is an instruction, make sure it dominates the loop preheader.
     // Otherwise we could end up with a use before def situation.
-    if (SCEVUnknown *SU = dyn_cast<SCEVUnknown>(AddRec->getOperand(1))) {
-      if (Instruction *I = dyn_cast<Instruction>(SU->getValue())) {
-        BasicBlock *StrideBB = I->getParent();
-        BasicBlock *Preheader = L->getLoopPreheader();
-        if (!DT->dominates(StrideBB, Preheader))
-          return false;
-      }
-    }
+    BasicBlock *Preheader = L->getLoopPreheader();
+    if (!AddRec->getOperand(1)->dominates(Preheader, DT))
+      return false;
 
     DOUT << "[" << L->getHeader()->getName()
          << "] Variable stride: " << *AddRec << "\n";