[LV] Move vector int induction update to end of latch

This patch moves the update instruction for vectorized integer induction phi
nodes to the end of the latch block. This ensures consistent placement of all
induction updates across all the kinds of int inductions we create (scalar,
splat vector, or vector phi).

Differential Revision: https://reviews.llvm.org/D22416

llvm-svn: 276339

1 files changed, 12 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index b6ba0796ed6..b5a751e7361 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -1910,14 +1910,23 @@ void InnerLoopVectorizer::createVectorIntInductionPHI(
   // factor. The last of those goes into the PHI.
   PHINode *VecInd = PHINode::Create(SteppedStart->getType(), 2, "vec.ind",
                                     &*LoopVectorBody->getFirstInsertionPt());
-  Value *LastInduction = VecInd;
+  Instruction *LastInduction = VecInd;
   for (unsigned Part = 0; Part < UF; ++Part) {
     Entry[Part] = LastInduction;
-    LastInduction = Builder.CreateAdd(LastInduction, SplatVF, "step.add");
+    LastInduction = cast<Instruction>(
+        Builder.CreateAdd(LastInduction, SplatVF, "step.add"));
   }
 
+  // Move the last step to the end of the latch block. This ensures consistent
+  // placement of all induction updates.
+  auto *LoopVectorLatch = LI->getLoopFor(LoopVectorBody)->getLoopLatch();
+  auto *Br = cast<BranchInst>(LoopVectorLatch->getTerminator());
+  auto *ICmp = cast<Instruction>(Br->getCondition());
+  LastInduction->moveBefore(ICmp);
+  LastInduction->setName("vec.ind.next");
+
   VecInd->addIncoming(SteppedStart, LoopVectorPreHeader);
-  VecInd->addIncoming(LastInduction, LoopVectorBody);
+  VecInd->addIncoming(LastInduction, LoopVectorLatch);
 }
 
 void InnerLoopVectorizer::widenIntInduction(PHINode *IV, VectorParts &Entry,