3 files changed, 25 insertions, 37 deletions

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 04ec67f5b3..9db46a8639 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2768,25 +2768,10 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
   // PHI's incoming blocks are in a different loop, in which case doing so
   // risks breaking LCSSA form. Instcombine would normally zap these, but
   // it doesn't have DominatorTree information, so it may miss cases.
-  if (Value *V = SimplifyInstruction(PN, TD, DT)) {
-    Instruction *I = dyn_cast<Instruction>(V);
-    // Only instructions are problematic for preserving LCSSA form.
-    if (!I)
+  if (Value *V = SimplifyInstruction(PN, TD, DT))
+    if (LI->replacementPreservesLCSSAForm(PN, V))
       return getSCEV(V);
 
-    // If the instruction is not defined in a loop, then it can be used freely.
-    Loop *ILoop = LI->getLoopFor(I->getParent());
-    if (!ILoop)
-      return getSCEV(I);
-
-    // If the instruction is defined in the same loop as the phi node, or in a
-    // loop that contains the phi node loop as an inner loop, then using it as
-    // a replacement for the phi node will not break LCSSA form.
-    Loop *PNLoop = LI->getLoopFor(PN->getParent());
-    if (ILoop->contains(PNLoop))
-      return getSCEV(I);
-  }
-
   // If it's not a loop phi, we can't handle it yet.
   return getUnknown(PN);
 }
diff --git a/lib/Transforms/Scalar/LoopUnswitch.cpp b/lib/Transforms/Scalar/LoopUnswitch.cpp
index 009ee7b95e..2eaeb438e0 100644
--- a/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -990,15 +990,16 @@ void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
       ++NumSimplify;
       continue;
     }
-    
+
     // See if instruction simplification can hack this up.  This is common for
     // things like "select false, X, Y" after unswitching made the condition be
     // 'false'.
-    if (Value *V = SimplifyInstruction(I, 0, DT)) {
-      ReplaceUsesOfWith(I, V, Worklist, L, LPM);
-      continue;
-    }
-    
+    if (Value *V = SimplifyInstruction(I, 0, DT))
+      if (LI->replacementPreservesLCSSAForm(I, V)) {
+        ReplaceUsesOfWith(I, V, Worklist, L, LPM);
+        continue;
+      }
+
     // Special case hacks that appear commonly in unswitched code.
     if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
       if (BI->isUnconditional()) {
diff --git a/lib/Transforms/Utils/LoopSimplify.cpp b/lib/Transforms/Utils/LoopSimplify.cpp
index 320223c247..f77a58300f 100644
--- a/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/lib/Transforms/Utils/LoopSimplify.cpp
@@ -269,11 +269,12 @@ ReprocessLoop:
   PHINode *PN;
   for (BasicBlock::iterator I = L->getHeader()->begin();
        (PN = dyn_cast<PHINode>(I++)); )
-    if (Value *V = SimplifyInstruction(PN, 0, DT)) {
-      if (AA) AA->deleteValue(PN);
-      PN->replaceAllUsesWith(V);
-      PN->eraseFromParent();
-    }
+    if (Value *V = SimplifyInstruction(PN, 0, DT))
+      if (LI->replacementPreservesLCSSAForm(PN, V)) {
+          if (AA) AA->deleteValue(PN);
+          PN->replaceAllUsesWith(V);
+          PN->eraseFromParent();
+      }
 
   // If this loop has multiple exits and the exits all go to the same
   // block, attempt to merge the exits. This helps several passes, such
@@ -445,17 +446,18 @@ static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
 /// PHI node that tells us how to partition the loops.
 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
-                                        AliasAnalysis *AA) {
+                                        AliasAnalysis *AA, LoopInfo *LI) {
   for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
     PHINode *PN = cast<PHINode>(I);
     ++I;
-    if (Value *V = SimplifyInstruction(PN, 0, DT)) {
-      // This is a degenerate PHI already, don't modify it!
-      PN->replaceAllUsesWith(V);
-      if (AA) AA->deleteValue(PN);
-      PN->eraseFromParent();
-      continue;
-    }
+    if (Value *V = SimplifyInstruction(PN, 0, DT))
+      if (LI->replacementPreservesLCSSAForm(PN, V)) {
+        // This is a degenerate PHI already, don't modify it!
+        PN->replaceAllUsesWith(V);
+        if (AA) AA->deleteValue(PN);
+        PN->eraseFromParent();
+        continue;
+      }
 
     // Scan this PHI node looking for a use of the PHI node by itself.
     for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
@@ -523,7 +525,7 @@ void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
 /// created.
 ///
 Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM) {
-  PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
+  PHINode *PN = FindPHIToPartitionLoops(L, DT, AA, LI);
   if (PN == 0) return 0;  // No known way to partition.
 
   // Pull out all predecessors that have varying values in the loop.  This