[LoopUnroll] Check partial unrolling is enabled before initialization. NFC.

[haicheng]

Summary

Check whether partial unrolling is enabled or not before initializing UP.Count for it.

[haicheng]

Upload the correct patch.

[mcrosier]

Ping.

[mcrosier]

Deferring review to Michael as I've never touched this pass.

[haicheng]

Hi Michael,

Would you please take a quick look at this simple change. I believe it is NFC. The main purpose is to improve the readability.

Haicheng

[mzolotukhin]

Looks good to me. Sorry for the delayed review!

Michael

llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp

if (canUnrollCompletely(L, UP.Threshold, 100, UP.DynamicCostSavingsDiscount,
           return ExplicitUnroll;
         }
     }
   }
 
   // 4rd priority is partial unrolling.
   // Try partial unroll only when TripCount could be staticaly calculated.
   if (TripCount) {
-    if (UP.Count == 0)
-      UP.Count = TripCount;
     UP.Partial |= ExplicitUnroll;
     if (!UP.Partial) {
       DEBUG(dbgs() << "  will not try to unroll partially because "
                    << "-unroll-allow-partial not given\n");
       UP.Count = 0;
       return false;
     }
+    if (UP.Count == 0)
+      UP.Count = TripCount;
     if (UP.PartialThreshold != NoThreshold) {
       // Reduce unroll count to be modulo of TripCount for partial unrolling.
       UnrolledSize = (uint64_t)(LoopSize - BEInsns) * UP.Count + BEInsns;
       if (UnrolledSize > UP.PartialThreshold)
         UP.Count = (std::max(UP.PartialThreshold, 3u) - BEInsns) /
                    (LoopSize - BEInsns);
       if (UP.Count > UP.MaxCount)
         UP.Count = UP.MaxCount;