[llvm] [MIPS]Remove unnecessary SLL instructions on MIPS64el (PR #109386)

[Craig Topper via llvm-commits]

================
@@ -1210,6 +1211,41 @@ static SDValue performSHLCombine(SDNode *N, SelectionDAG &DAG,
                      DAG.getConstant(SMSize, DL, MVT::i32));
 }
 
+static SDValue performSignExtendCombine(SDNode *N, SelectionDAG &DAG, TargetLowering::DAGCombinerInfo &DCI,const MipsSubtarget &Subtarget) {
+  if (DCI.Level != AfterLegalizeDAG) {
+    return SDValue();
+  }
+
+  if (!Subtarget.isGP64bit()) {
+    return SDValue();
+  }
+
+  SDValue N0 = N->getOperand(0);
+  EVT VT = N->getValueType(0);
+
+  if (N0->getNumOperands() != 2) {
+    return SDValue();
+  }
+
+  // Pattern match XOR.
+  //  $dst = (sign_extend (xor (trunc $src, i32), -1), i64)
+  //  => $dst = (xor ($src, -1), i64)
+  if (N0.getOpcode() == ISD::XOR &&
+      N0.getOperand(0).getOpcode() == ISD::TRUNCATE &&
+      N0.getOperand(1).getOpcode() == ISD::Constant) {
+    SDValue TruncateOperand = N0.getOperand(0).getOperand(0);
+    if (VT == MVT::i64 && VT == TruncateOperand->getValueType(0)) {
+      APInt MinusOne(32, -1, true);
+      if (N0.getConstantOperandAPInt(1) == MinusOne) {
+        return DAG.getNode(ISD::XOR, SDLoc(N0), VT, TruncateOperand,
+                           DAG.getTargetConstant(-1, SDLoc(N0), VT));
----------------
topperc wrote:

This should not be a target constant. TargetConstant should only nodes that always take an immediate for that operand.

https://github.com/llvm/llvm-project/pull/109386