[DAGCombiner] If a TokenFactor would be merged into its user, consider the user later.

Summary:
A number of optimizations are inhibited by single-use TokenFactors not
being merged into the TokenFactor using it. This makes we consider if
we can do the merge immediately.

Most tests changes here are due to the change in visitation causing
minor reorderings and associated reassociation of paired memory
operations.

CodeGen tests with non-reordering changes:

  X86/aligned-variadic.ll -- memory-based add folded into stored leaq
  value.

  X86/constant-combiners.ll -- Optimizes out overlap between stores.

  X86/pr40631_deadstore_elision -- folds constant byte store into
  preceding quad word constant store.

Reviewers: RKSimon, craig.topper, spatel, efriedma, courbet

Reviewed By: courbet

Subscribers: dylanmckay, sdardis, nemanjai, jvesely, nhaehnle, javed.absar, eraman, hiraditya, kbarton, jrtc27, atanasyan, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59260

llvm-svn: 356068

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 9ff62ad7fec..1095b413072 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1709,6 +1709,12 @@ SDValue DAGCombiner::visitTokenFactor(SDNode *N) {
   if (OptLevel == CodeGenOpt::None)
     return SDValue();
 
+  // If this is used only a single token factor, we should make sure we have a
+  // chance to merge them together. This prevents TF chains from inhibiting
+  // optimizations.
+  if (N->hasOneUse() && N->use_begin()->getOpcode() == ISD::TokenFactor)
+    AddToWorklist(*(N->use_begin()));
+
   SmallVector<SDNode *, 8> TFs;     // List of token factors to visit.
   SmallVector<SDValue, 8> Ops;      // Ops for replacing token factor.
   SmallPtrSet<SDNode*, 16> SeenOps;