[llvm] r204699 - SLP vectorizer: Don't hoist vector extracts of phis.

[Andrew Trick]

Author: atrick
Date: Mon Mar 24 21:18:47 2014
New Revision: 204699

URL: http://llvm.org/viewvc/llvm-project?rev=204699&view=rev
Log:
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.

Modified:
    llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp

Modified: llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp?rev=204699&r1=204698&r2=204699&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp Mon Mar 24 21:18:47 2014
@@ -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) {