[llvm] [RISCV][llvm] Preliminary P extension codegen support (PR #162668)

[Brandon Wu via llvm-commits]

================
@@ -15996,11 +16137,88 @@ static SDValue combineTruncSelectToSMaxUSat(SDNode *N, SelectionDAG &DAG) {
   return DAG.getNode(ISD::TRUNCATE, DL, VT, Min);
 }
 
+// Handle P extension averaging subtraction pattern:
+// (vXiY (trunc (srl (sub ([s|z]ext vXiY:$a), ([s|z]ext vXiY:$b)), 1)))
+// -> PASUB/PASUBU
+static SDValue combinePExtTruncate(SDNode *N, SelectionDAG &DAG,
+                                   const RISCVSubtarget &Subtarget) {
+  SDValue N0 = N->getOperand(0);
+  EVT VT = N->getValueType(0);
+  if (!Subtarget.hasStdExtP() || !VT.isFixedLengthVector())
----------------
4vtomat wrote:

Yeah, I should remove it

https://github.com/llvm/llvm-project/pull/162668