[vectorizer] Clean up the handling of unvectorized loop unrolling in the

LoopVectorize pass.

The logic here doesn't make much sense. We *only* unrolled if the
unvectorized loop was a reduction loop with a single basic block *and*
small loop body. The reduction part in particular doesn't make much
sense. Instead, if we just fall through to the vectorized unroll logic
it makes more sense of unrolling if there is a vectorized reduction that
could be hacked on by the SLP vectorizer *or* if the loop is small.

This is mostly a cleanup and nothing in the test suite really exercises
this, but I did run benchmarks across this change and saw no really
significant changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200198 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 3 insertions, 13 deletions

diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index 9db66e7e69..66134bd95d 100644
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -4995,19 +4995,9 @@ LoopVectorizationCostModel::selectUnrollFactor(bool OptForSize,
   else if (UF < 1)
     UF = 1;
 
-  bool HasReductions = Legal->getReductionVars()->size();
-
-  // Decide if we want to unroll if we decided that it is legal to vectorize
-  // but not profitable.
-  if (VF == 1) {
-    if (TheLoop->getNumBlocks() > 1 || !HasReductions ||
-        LoopCost > SmallLoopCost)
-      return 1;
-
-    return UF;
-  }
-
-  if (HasReductions) {
+  // Unroll if we vectorized this loop and there is a reduction that could
+  // benefit from unrolling.
+  if (VF > 1 && Legal->getReductionVars()->size()) {
     DEBUG(dbgs() << "LV: Unrolling because of reductions.\n");
     return UF;
   }