SLP Vectorier: Don't vectorize really short chains because they are already handled by the SelectionDAG store-vectorizer, which does a better job in deciding when to vectorize.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187267 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 2 deletions

diff --git a/lib/Transforms/Vectorize/SLPVectorizer.cpp b/lib/Transforms/Vectorize/SLPVectorizer.cpp
index c1accd32c5..50e37e9916 100644
--- a/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -898,8 +898,12 @@ int BoUpSLP::getTreeCost() {
   DEBUG(dbgs() << "SLP: Calculating cost for tree of size " <<
         VectorizableTree.size() << ".\n");
 
-  if (!VectorizableTree.size()) {
-    assert(!ExternalUses.size() && "We should not have any external users");
+  // Don't vectorize tiny trees. Small load/store chains or consecutive stores
+  // of constants will be vectoried in SelectionDAG in MergeConsecutiveStores.
+  if (VectorizableTree.size() < 3) {
+    if (!VectorizableTree.size()) {
+      assert(!ExternalUses.size() && "We should not have any external users");
+    }
     return 0;
   }