[Unroll] When completely unrolling the loop, replace conditinal branches with unconditional.

[mzolotukhin]

Summary

I see no reasons why we don't do this at the moment (or I'm misreading
the code). Later clean-ups replace conditional branches anyway, but
that's unnecessary work. It might be even more relevant if we unroll
loops with relatively high trip-count.

Does this patch make sense?

[mzolotukhin]

Ping.

[hfinkel]

Yes, this seems to make sense.

[mzolotukhin]

Thanks, Hal!

llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp

for (unsigned i = 0, e = Latches.size(); i != e; ++i) {
     bool NeedConditional = true;
 
     if (RuntimeTripCount && j != 0) {
       NeedConditional = false;
     }
 
     // For a complete unroll, make the last iteration end with a branch
     // to the exit block.
-    if (CompletelyUnroll && j == 0) {
+    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)) {
       NeedConditional = false;
     }