Instead of a vector load, shuffle and then extract an element. Load the element from address with an offset.

        pshufd $1, (%rdi), %xmm0
        movd %xmm0, %eax
=>
        movl 4(%rdi), %eax


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51026 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index f05f4445a8..058e60f5fc 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1838,6 +1838,28 @@ bool SelectionDAG::isVerifiedDebugInfoDesc(SDOperand Op) const {
 }
 
 
+/// getShuffleScalarElt - Returns the scalar element that will make up the ith
+/// element of the result of the vector shuffle.
+SDOperand SelectionDAG::getShuffleScalarElt(const SDNode *N, unsigned Idx) {
+  MVT::ValueType VT = N->getValueType(0);
+  SDOperand PermMask = N->getOperand(2);
+  unsigned NumElems = PermMask.getNumOperands();
+  SDOperand V = (Idx < NumElems) ? N->getOperand(0) : N->getOperand(1);
+  Idx %= NumElems;
+  if (V.getOpcode() == ISD::SCALAR_TO_VECTOR) {
+    return (Idx == 0)
+     ? V.getOperand(0) : getNode(ISD::UNDEF, MVT::getVectorElementType(VT));
+  }
+  if (V.getOpcode() == ISD::VECTOR_SHUFFLE) {
+    SDOperand Elt = PermMask.getOperand(Idx);
+    if (Elt.getOpcode() == ISD::UNDEF)
+      return getNode(ISD::UNDEF, MVT::getVectorElementType(VT));
+    return getShuffleScalarElt(V.Val,cast<ConstantSDNode>(Elt)->getValue());
+  }
+  return SDOperand();
+}
+
+
 /// getNode - Gets or creates the specified node.
 ///
 SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT) {