1 files changed, 34 insertions, 24 deletions

diff --git a/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index 91395b2..09a186f 100644
--- a/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -40,10 +40,9 @@ UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden,
   cl::desc("Allows loops to be partially unrolled until "
            "-unroll-threshold loop size is reached."));
 
-// Temporary flag to be removed in 3.0
 static cl::opt<bool>
-NoSCEVUnroll("disable-unroll-scev", cl::init(false), cl::Hidden,
-  cl::desc("Use ScalarEvolution to analyze loop trip counts for unrolling"));
+UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden,
+  cl::desc("Unroll loops with run-time trip counts"));
 
 namespace {
   class LoopUnroll : public LoopPass {
@@ -68,6 +67,10 @@ namespace {
     // explicit -unroll-threshold).
     static const unsigned OptSizeUnrollThreshold = 50;
 
+    // Default unroll count for loops with run-time trip count if
+    // -unroll-count is not set
+    static const unsigned UnrollRuntimeCount = 8;
+
     unsigned CurrentCount;
     unsigned CurrentThreshold;
     bool     CurrentAllowPartial;
@@ -101,6 +104,7 @@ INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
 INITIALIZE_PASS_DEPENDENCY(LCSSA)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
 INITIALIZE_PASS_END(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
 
 Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial) {
@@ -147,23 +151,21 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
   // Find trip count and trip multiple if count is not available
   unsigned TripCount = 0;
   unsigned TripMultiple = 1;
-  if (!NoSCEVUnroll) {
-    // Find "latch trip count". UnrollLoop assumes that control cannot exit
-    // via the loop latch on any iteration prior to TripCount. The loop may exit
-    // early via an earlier branch.
-    BasicBlock *LatchBlock = L->getLoopLatch();
-    if (LatchBlock) {
-      TripCount = SE->getSmallConstantTripCount(L, LatchBlock);
-      TripMultiple = SE->getSmallConstantTripMultiple(L, LatchBlock);
-    }
-  }
-  else {
-    TripCount = L->getSmallConstantTripCount();
-    if (TripCount == 0)
-      TripMultiple = L->getSmallConstantTripMultiple();
+  // Find "latch trip count". UnrollLoop assumes that control cannot exit
+  // via the loop latch on any iteration prior to TripCount. The loop may exit
+  // early via an earlier branch.
+  BasicBlock *LatchBlock = L->getLoopLatch();
+  if (LatchBlock) {
+    TripCount = SE->getSmallConstantTripCount(L, LatchBlock);
+    TripMultiple = SE->getSmallConstantTripMultiple(L, LatchBlock);
   }
-  // Automatically select an unroll count.
+  // Use a default unroll-count if the user doesn't specify a value
+  // and the trip count is a run-time value.  The default is different
+  // for run-time or compile-time trip count loops.
   unsigned Count = CurrentCount;
+  if (UnrollRuntime && CurrentCount == 0 && TripCount == 0)
+    Count = UnrollRuntimeCount;
+
   if (Count == 0) {
     // Conservative heuristic: if we know the trip count, see if we can
     // completely unroll (subject to the threshold, checked below); otherwise
@@ -188,15 +190,23 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
     if (TripCount != 1 && Size > Threshold) {
       DEBUG(dbgs() << "  Too large to fully unroll with count: " << Count
             << " because size: " << Size << ">" << Threshold << "\n");
-      if (!CurrentAllowPartial) {
+      if (!CurrentAllowPartial && !(UnrollRuntime && TripCount == 0)) {
         DEBUG(dbgs() << "  will not try to unroll partially because "
               << "-unroll-allow-partial not given\n");
         return false;
       }
-      // Reduce unroll count to be modulo of TripCount for partial unrolling
-      Count = Threshold / LoopSize;
-      while (Count != 0 && TripCount%Count != 0) {
-        Count--;
+      if (TripCount) {
+        // Reduce unroll count to be modulo of TripCount for partial unrolling
+        Count = Threshold / LoopSize;
+        while (Count != 0 && TripCount%Count != 0)
+          Count--;
+      }
+      else if (UnrollRuntime) {
+        // Reduce unroll count to be a lower power-of-two value
+        while (Count != 0 && Size > Threshold) {
+          Count >>= 1;
+          Size = LoopSize*Count;
+        }
       }
       if (Count < 2) {
         DEBUG(dbgs() << "  could not unroll partially\n");
@@ -207,7 +217,7 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
   }
 
   // Unroll the loop.
-  if (!UnrollLoop(L, Count, TripCount, TripMultiple, LI, &LPM))
+  if (!UnrollLoop(L, Count, TripCount, UnrollRuntime, TripMultiple, LI, &LPM))
     return false;
 
   return true;