NFC: Add debug tracing for more cases where loop unrolling fails.

llvm-svn: 293313

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 5c3c94008d3..4fc7f410412 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -306,8 +306,10 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount, bool Force,
     Count = TripCount;
 
   // Don't enter the unroll code if there is nothing to do.
-  if (TripCount == 0 && Count < 2 && PeelCount == 0)
+  if (TripCount == 0 && Count < 2 && PeelCount == 0) {
+    DEBUG(dbgs() << "Won't unroll; almost nothing to do\n");
     return false;
+  }
 
   assert(Count > 0);
   assert(TripMultiple > 0);
@@ -362,8 +364,12 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount, bool Force,
                                   PreserveLCSSA)) {
     if (Force)
       RuntimeTripCount = false;
-    else
+    else {
+      DEBUG(
+          dbgs() << "Wont unroll; prolog and epilog code could not be inserted "
+                    "when assuming runtime trip count\n");
       return false;
+    }
   }
 
   // Notify ScalarEvolution that the loop will be substantially changed,