When optimizing certain BUILD_VECTOR nodes into other BUILD_VECTOR nodes, add the new node into the work list because there is a potential for further optimizations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152784 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 14 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 8337d76..32b9fa4 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7422,6 +7422,8 @@ SDValue DAGCombiner::visitBUILD_VECTOR(SDNode *N) {
   // will be type-legalized to complex code sequences.
   // We perform this optimization only before the operation legalizer because we
   // may introduce illegal operations.
+  // Create a new simpler BUILD_VECTOR sequence which other optimizations can
+  // turn into a single shuffle instruction.
   if ((Level == AfterLegalizeVectorOps || Level == AfterLegalizeTypes) &&
       ValidTypes) {
     bool isLE = TLI.isLittleEndian();
@@ -7462,6 +7464,8 @@ SDValue DAGCombiner::visitBUILD_VECTOR(SDNode *N) {
     SDValue BV = DAG.getNode(ISD::BUILD_VECTOR, N->getDebugLoc(),
                                  VecVT, &Ops[0], Ops.size());
 
+    // The new BUILD_VECTOR node has the potential to be further optimized.
+    AddToWorkList(BV.getNode());
     // Bitcast to the desired type.
     return DAG.getNode(ISD::BITCAST, dl, N->getValueType(0), BV);
   }
diff --git a/test/CodeGen/X86/2012-03-15-build_vector_wl.ll b/test/CodeGen/X86/2012-03-15-build_vector_wl.ll
new file mode 100644
index 0000000..fec17e9
--- /dev/null
+++ b/test/CodeGen/X86/2012-03-15-build_vector_wl.ll
@@ -0,0 +1,10 @@
+
+; RUN: llc < %s -mtriple=x86_64-apple-darwin -mcpu=corei7-avx -mattr=+avx | FileCheck %s
+; CHECK: build_vector_again
+define <4 x i8> @build_vector_again(<16 x i8> %in) nounwind readnone {
+entry:
+  %out = shufflevector <16 x i8> %in, <16 x i8> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK: shufb
+  ret <4 x i8> %out
+; CHECK: ret
+}