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

[Craig Topper via llvm-commits]

================
@@ -14889,6 +15012,24 @@ void RISCVTargetLowering::ReplaceNodeResults(SDNode *N,
     Results.push_back(DAG.getNode(ISD::TRUNCATE, DL, VT, NewRes));
     break;
   }
+  case RISCVISD::PASUB:
+  case RISCVISD::PASUBU: {
+    MVT VT = N->getSimpleValueType(0);
+    SDValue Op0 = N->getOperand(0);
+    SDValue Op1 = N->getOperand(1);
+    assert(VT == MVT::v2i16 || VT == MVT::v4i8);
+    MVT NewVT = MVT::v4i16;
+    if (VT == MVT::v4i8)
+      NewVT = MVT::v8i8;
+    Op0 =  DAG.getBitcast(MVT::i32, Op0);
----------------
topperc wrote:

The CONCAT_VECTORS should get removed by the type legalizer when it widens the surrounding operations. Leaving just v8i8 or v4i16 vector operations except for loads/stores. If you go through a bitcast to scalar, the type legalizer can't delete them.

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