Teach DAGCombiner how to fold a SIGN_EXTEND_INREG of a BUILD_VECTOR of

ConstantSDNodes (or UNDEFs) into a simple BUILD_VECTOR.

For example, given the following sequence of dag nodes:

  i32 C = Constant<1>
  v4i32 V = BUILD_VECTOR C, C, C, C
  v4i32 Result = SIGN_EXTEND_INREG V, ValueType:v4i1

The SIGN_EXTEND_INREG node can be folded into a build_vector since
the vector in input is a BUILD_VECTOR of constants.

The optimized sequence is:

  i32 C = Constant<-1>
  v4i32 Result = BUILD_VECTOR C, C, C, C

llvm-svn: 198084

1 files changed, 16 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 45d5a4fa69e..f163f6bdf2c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -179,6 +179,22 @@ bool ISD::isBuildVectorAllZeros(const SDNode *N) {
   return true;
 }
 
+/// \brief Return true if the specified node is a BUILD_VECTOR node of
+/// all ConstantSDNode or undef.
+bool ISD::isBuildVectorOfConstantSDNodes(const SDNode *N) {
+  if (N->getOpcode() != ISD::BUILD_VECTOR)
+    return false;
+
+  for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
+    SDValue Op = N->getOperand(i);
+    if (Op.getOpcode() == ISD::UNDEF)
+      continue;
+    if (!isa<ConstantSDNode>(Op))
+      return false;
+  }
+  return true;
+}
+
 /// isScalarToVector - Return true if the specified node is a
 /// ISD::SCALAR_TO_VECTOR node or a BUILD_VECTOR node where only the low
 /// element is not an undef.