1 files changed, 18 insertions, 9 deletions
diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 77b744ec881..847224753f4 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -187,6 +187,10 @@ static bool needToInsertPhisForLCSSA(Loop *L, std::vector<BasicBlock *> Blocks,
 /// iterations via an early branch, but control may not exit the loop from the
 /// LatchBlock's terminator prior to TripCount iterations.
 ///
+/// PreserveCondBr indicates whether the conditional branch of the LatchBlock
+/// needs to be preserved.  It is needed when we use trip count upper bound to
+/// fully unroll the loop.
+///
 /// Similarly, TripMultiple divides the number of times that the LatchBlock may
 /// execute without exiting the loop.
 ///
@@ -203,9 +207,10 @@ static bool needToInsertPhisForLCSSA(Loop *L, std::vector<BasicBlock *> Blocks,
 /// DominatorTree if they are non-null.
 bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount, bool Force,
                       bool AllowRuntime, bool AllowExpensiveTripCount,
-                      unsigned TripMultiple, LoopInfo *LI, ScalarEvolution *SE,
-                      DominatorTree *DT, AssumptionCache *AC,
-                      OptimizationRemarkEmitter *ORE, bool PreserveLCSSA) {
+                      bool PreserveCondBr, unsigned TripMultiple, LoopInfo *LI,
+                      ScalarEvolution *SE, DominatorTree *DT,
+                      AssumptionCache *AC, OptimizationRemarkEmitter *ORE,
+                      bool PreserveLCSSA) {
   BasicBlock *Preheader = L->getLoopPreheader();
   if (!Preheader) {
     DEBUG(dbgs() << "  Can't unroll; loop preheader-insertion failed.\n");
@@ -539,12 +544,16 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount, bool Force,
     if (CompletelyUnroll) {
       if (j == 0)
         Dest = LoopExit;
-      NeedConditional = false;
-    }
-
-    // If we know the trip count or a multiple of it, we can safely use an
-    // unconditional branch for some iterations.
-    if (j != BreakoutTrip && (TripMultiple == 0 || j % TripMultiple != 0)) {
+      // If using trip count upper bound to completely unroll, we need to keep
+      // the conditional branch except the last one because the loop may exit
+      // after any iteration.
+      assert(NeedConditional &&
+             "NeedCondition cannot be modified by both complete "
+             "unrolling and runtime unrolling");
+      NeedConditional = (PreserveCondBr && j);
+    } else if (j != BreakoutTrip && (TripMultiple == 0 || j % TripMultiple != 0)) {
+      // If we know the trip count or a multiple of it, we can safely use an
+      // unconditional branch for some iterations.
       NeedConditional = false;
     }