When a value is used multiple times within a single PHI, instructions

inserted to replace that value must dominate all of of the basic
blocks associated with the uses of the value in the PHI, not just
one of them.

llvm-svn: 74376

1 files changed, 15 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index d2ba25637e0..27e377f9037 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -70,6 +70,7 @@ namespace {
     IVUsers         *IU;
     LoopInfo        *LI;
     ScalarEvolution *SE;
+    DominatorTree   *DT;
     bool Changed;
   public:
 
@@ -329,6 +330,7 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
   IU = &getAnalysis<IVUsers>();
   LI = &getAnalysis<LoopInfo>();
   SE = &getAnalysis<ScalarEvolution>();
+  DT = &getAnalysis<DominatorTree>();
   Changed = false;
 
   // If there are any floating-point recurrences, attempt to
@@ -479,12 +481,22 @@ void IndVarSimplify::RewriteIVExpressions(Loop *L, const Type *LargestType,
       if (!AR->isLoopInvariant(L) && !Stride->isLoopInvariant(L))
         continue;
 
+      // Determine the insertion point for this user. By default, insert
+      // immediately before the user. The SCEVExpander class will automatically
+      // hoist loop invariants out of the loop. For PHI nodes, there may be
+      // multiple uses, so compute the nearest common dominator for the
+      // incoming blocks.
       Instruction *InsertPt = User;
       if (PHINode *PHI = dyn_cast<PHINode>(InsertPt))
-        for (unsigned i = 0; ; ++i)
+        for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
           if (PHI->getIncomingValue(i) == Op) {
-            InsertPt = PHI->getIncomingBlock(i)->getTerminator();
-            break;
+            if (InsertPt == User)
+              InsertPt = PHI->getIncomingBlock(i)->getTerminator();
+            else
+              InsertPt =
+                DT->findNearestCommonDominator(InsertPt->getParent(),
+                                               PHI->getIncomingBlock(i))
+                      ->getTerminator();
           }
 
       // Now expand it into actual Instructions and patch it into place.