[llvm] [NVPTX] Prefer prmt.b32 over bfi.b32 (PR #110766)

[Artem Belevich via llvm-commits]

================
@@ -2328,20 +2328,23 @@ SDValue NVPTXTargetLowering::LowerBUILD_VECTOR(SDValue Op,
     // Lower non-const v4i8 vector as byte-wise constructed i32, which allows us
     // to optimize calculation of constant parts.
     if (VT == MVT::v4i8) {
-      SDValue C8 = DAG.getConstant(8, DL, MVT::i32);
-      SDValue E01 = DAG.getNode(
-          NVPTXISD::BFI, DL, MVT::i32,
-          DAG.getAnyExtOrTrunc(Op->getOperand(1), DL, MVT::i32),
-          DAG.getAnyExtOrTrunc(Op->getOperand(0), DL, MVT::i32), C8, C8);
-      SDValue E012 =
-          DAG.getNode(NVPTXISD::BFI, DL, MVT::i32,
-                      DAG.getAnyExtOrTrunc(Op->getOperand(2), DL, MVT::i32),
-                      E01, DAG.getConstant(16, DL, MVT::i32), C8);
-      SDValue E0123 =
-          DAG.getNode(NVPTXISD::BFI, DL, MVT::i32,
-                      DAG.getAnyExtOrTrunc(Op->getOperand(3), DL, MVT::i32),
-                      E012, DAG.getConstant(24, DL, MVT::i32), C8);
-      return DAG.getNode(ISD::BITCAST, DL, VT, E0123);
+      SDValue PRMT__10 = DAG.getNode(
+          NVPTXISD::PRMT, DL, MVT::v4i8,
+          {DAG.getAnyExtOrTrunc(Op->getOperand(0), DL, MVT::i32),
+           DAG.getAnyExtOrTrunc(Op->getOperand(1), DL, MVT::i32),
+           DAG.getConstant(0x3340, DL, MVT::i32),
+           DAG.getConstant(NVPTX::PTXPrmtMode::NONE, DL, MVT::i32)});
+      SDValue PRMT_210 = DAG.getNode(
+          NVPTXISD::PRMT, DL, MVT::v4i8,
+          {PRMT__10, DAG.getAnyExtOrTrunc(Op->getOperand(2), DL, MVT::i32),
+           DAG.getConstant(0x3410, DL, MVT::i32),
+           DAG.getConstant(NVPTX::PTXPrmtMode::NONE, DL, MVT::i32)});
+      SDValue PRMT3210 = DAG.getNode(
----------------
Artem-B wrote:

Converting from `v = prmt(d, prmt(c, prmt(a,b)))` to `v = prmt(prmt(c,d), prmt(a,b))` may squeeze a bit more performance here if GPU can do two leaf permutes in parallel as they are independent.

https://github.com/llvm/llvm-project/pull/110766