[LV] Remove implicit single basic block assumption

This patch is part of D28975's breakdown - no change in output intended.

LV's code currently assumes the vectorized loop is a single basic block up
until predicateInstructions() is called. This patch removes two manifestations
of this assumption (loop phi incoming values, dominator tree update) by
replacing the use of vectorLoopBody with the vectorized loop's latch/header.

Differential Revision: https://reviews.llvm.org/D32040

llvm-svn: 300310

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -4200,7 +4200,7 @@ void InnerLoopVectorizer::fixReduction(PHINode *Phi) {
     cast<PHINode>(VecRdxPhi[part])
       ->addIncoming(StartVal, LoopVectorPreHeader);
     cast<PHINode>(VecRdxPhi[part])
-      ->addIncoming(Val[part], LoopVectorBody);
+      ->addIncoming(Val[part], LI->getLoopFor(LoopVectorBody)->getLoopLatch());
   }
 
   // Before each round, move the insertion point right between
@@ -5059,11 +5059,10 @@ void InnerLoopVectorizer::updateAnalysis() {
   assert(DT->properlyDominates(LoopBypassBlocks.front(), LoopExitBlock) &&
          "Entry does not dominate exit.");
 
-  // We don't predicate stores by this point, so the vector body should be a
-  // single loop.
-  DT->addNewBlock(LoopVectorBody, LoopVectorPreHeader);
-
-  DT->addNewBlock(LoopMiddleBlock, LoopVectorBody);
+  DT->addNewBlock(LI->getLoopFor(LoopVectorBody)->getHeader(),
+                  LoopVectorPreHeader);
+  DT->addNewBlock(LoopMiddleBlock,
+                  LI->getLoopFor(LoopVectorBody)->getLoopLatch());
   DT->addNewBlock(LoopScalarPreHeader, LoopBypassBlocks[0]);
   DT->changeImmediateDominator(LoopScalarBody, LoopScalarPreHeader);
   DT->changeImmediateDominator(LoopExitBlock, LoopBypassBlocks[0]);