Enable unroll for constant bound loops when TripCount is not modulo of unroll factor, reducing it to maximum power-of-2 that satisfies threshold limit.
Commit for Evgeny Stupachenko (evstupac@gmail.com)
Differential Revision: http://reviews.llvm.org/D18290
llvm-svn: 265337
diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index c3761dcf..fa6214f 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -639,6 +639,16 @@
Count = (std::max(UP.PartialThreshold, 3u) - 2) / (LoopSize - 2);
while (Count != 0 && TripCount % Count != 0)
Count--;
+ if (Count <= 1) {
+ // If there is no Count that is modulo of TripCount, set Count to
+ // largest power-of-two factor that satisfies the threshold limit.
+ Count = (std::max(UP.PartialThreshold, 3u) - 2) / (LoopSize - 2);
+ UnrolledSize = (LoopSize - 2) * Count + 2;
+ while (Count != 0 && UnrolledSize > UP.PartialThreshold) {
+ Count >>= 1;
+ UnrolledSize = (LoopSize - 2) * Count + 2;
+ }
+ }
}
} else if (Unrolling == Runtime) {
if (!AllowRuntime && !CountSetExplicitly) {