SLP vectorizer: Don't hoist vector extracts of phis.

Extracts coming from phis were being hoisted, while all others were
sunk to their uses. This was inconsistent and didn't seem to serve a
purpose. Changing all extracts to be sunk to uses is a prerequisite
for adding block frequency to the SLP vectorizer's cost model.

I benchmarked the change in isolation (without block frequency). I
only saw noise on x86 and some potentially significant improvements on
ARM. No major regressions is good enough for me.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204699 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Vectorize/SLPVectorizer.cpp b/lib/Transforms/Vectorize/SLPVectorizer.cpp
index bd9c5c75cc31f5e37b4ad4b5b7bd53ccee638143..97b34f476e692896c3cdd840670e622013b5a5f3 100644 (file)
--- a/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -1690,12 +1690,7 @@ Value *BoUpSLP::vectorizeTree() {
     Value *Lane = Builder.getInt32(it->Lane);
     // Generate extracts for out-of-tree users.
     // Find the insertion point for the extractelement lane.
-    if (PHINode *PN = dyn_cast<PHINode>(Vec)) {
-      Builder.SetInsertPoint(PN->getParent()->getFirstInsertionPt());
-      Value *Ex = Builder.CreateExtractElement(Vec, Lane);
-      CSEBlocks.insert(PN->getParent());
-      User->replaceUsesOfWith(Scalar, Ex);
-    } else if (isa<Instruction>(Vec)){
+    if (isa<Instruction>(Vec)){
       if (PHINode *PH = dyn_cast<PHINode>(User)) {
         for (int i = 0, e = PH->getNumIncomingValues(); i != e; ++i) {
           if (PH->getIncomingValue(i) == Scalar) {