1 files changed, 21 insertions, 2 deletions
diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index 513c5a4dc51..159ed201ab3 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -543,11 +543,14 @@ analyzeLoopUnrollCost(const Loop *L, unsigned TripCount, ScalarEvolution &SE,
   // unrolling.
   unsigned RolledDynamicCost = 0;
 
+  DEBUG(dbgs() << "Starting LoopUnroll profitability analysis...\n");
+
   // Simulate execution of each iteration of the loop counting instructions,
   // which would be simplified.
   // Since the same load will take different values on different iterations,
   // we literally have to go through all loop's iterations.
   for (unsigned Iteration = 0; Iteration < TripCount; ++Iteration) {
+    DEBUG(dbgs() << " Analyzing iteration " << Iteration << "\n");
     SimplifiedValues.clear();
     UnrolledInstAnalyzer Analyzer(Iteration, SimplifiedValues, L, SE);
 
@@ -568,14 +571,24 @@ analyzeLoopUnrollCost(const Loop *L, unsigned TripCount, ScalarEvolution &SE,
         // unrolled cost.
         if (!Analyzer.visit(I))
           UnrolledCost += InstCost;
+        else {
+          DEBUG(dbgs() << "  " << I
+                       << " would be simplified if loop is unrolled.\n");
+          (void)0;
+        }
 
         // Also track this instructions expected cost when executing the rolled
         // loop form.
         RolledDynamicCost += InstCost;
 
         // If unrolled body turns out to be too big, bail out.
-        if (UnrolledCost > MaxUnrolledLoopSize)
+        if (UnrolledCost > MaxUnrolledLoopSize) {
+          DEBUG(dbgs() << "  Exceeded threshold.. exiting.\n"
+                       << "  UnrolledCost: " << UnrolledCost
+                       << ", MaxUnrolledLoopSize: " << MaxUnrolledLoopSize
+                       << "\n");
           return None;
+        }
       }
 
       TerminatorInst *TI = BB->getTerminator();
@@ -612,9 +625,15 @@ analyzeLoopUnrollCost(const Loop *L, unsigned TripCount, ScalarEvolution &SE,
 
     // If we found no optimization opportunities on the first iteration, we
     // won't find them on later ones too.
-    if (UnrolledCost == RolledDynamicCost)
+    if (UnrolledCost == RolledDynamicCost) {
+      DEBUG(dbgs() << "  No opportunities found.. exiting.\n"
+                   << "  UnrolledCost: " << UnrolledCost << "\n");
       return None;
+    }
   }
+  DEBUG(dbgs() << "Analysis finished:\n"
+               << "UnrolledCost: " << UnrolledCost << ", "
+               << "RolledDynamicCost: " << RolledDynamicCost << "\n");
   return {{UnrolledCost, RolledDynamicCost}};
 }