[llvm] [AArch64] Utilize `XAR` for certain vector rotates (PR #137629)

[Rajveer Singh Bharadwaj via llvm-commits]

https://github.com/Rajveer100 updated https://github.com/llvm/llvm-project/pull/137629

>From 9c2648d44d5364b53314d25bc957b6788f0f0e94 Mon Sep 17 00:00:00 2001
From: Rajveer <rajveer.developer at icloud.com>
Date: Mon, 28 Apr 2025 18:42:32 +0530
Subject: [PATCH] [AArch64] Utilize `XAR` for certain vector rotates

Resolves #137162

For cases when there isn't any `XOR` in the transformation,
replace with a zero register.
---
 .../Target/AArch64/AArch64ISelDAGToDAG.cpp    | 50 ++++++++++++++-----
 llvm/test/CodeGen/AArch64/sve2-xar.ll         | 13 +++--
 2 files changed, 44 insertions(+), 19 deletions(-)

diff --git a/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp b/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
index 40944e3d43d6b..8e8647e219883 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
@@ -4532,7 +4532,9 @@ bool AArch64DAGToDAGISel::trySelectXAR(SDNode *N) {
 
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
+
   EVT VT = N->getValueType(0);
+  SDLoc DL(N);
 
   // Essentially: rotr (xor(x, y), imm) -> xar (x, y, imm)
   // Rotate by a constant is a funnel shift in IR which is exanded to
@@ -4558,10 +4560,26 @@ bool AArch64DAGToDAGISel::trySelectXAR(SDNode *N) {
         !TLI->isAllActivePredicate(*CurDAG, N1.getOperand(0)))
       return false;
 
-    SDValue XOR = N0.getOperand(1);
-    if (XOR.getOpcode() != ISD::XOR || XOR != N1.getOperand(1))
+    if (N0.getOperand(1) != N1.getOperand(1))
       return false;
 
+    SDValue R1, R2;
+    if (N0.getOperand(1).getOpcode() != ISD::XOR) {
+      SDValue Zero = CurDAG->getTargetConstant(0, DL, MVT::i64);
+      SDNode *MOV = CurDAG->getMachineNode(AArch64::MOVIv2d_ns, DL, VT, Zero);
+      SDValue MOVIV = SDValue(MOV, 0);
+
+      SDValue ZSub = CurDAG->getTargetConstant(AArch64::zsub, DL, MVT::i32);
+      SDNode *SubRegToReg = CurDAG->getMachineNode(AArch64::SUBREG_TO_REG, DL,
+                                                   VT, Zero, MOVIV, ZSub);
+
+      R1 = N1->getOperand(1);
+      R2 = SDValue(SubRegToReg, 0);
+    } else {
+      R1 = N0.getOperand(1).getOperand(0);
+      R2 = N1.getOperand(1).getOperand(1);
+    }
+
     APInt ShlAmt, ShrAmt;
     if (!ISD::isConstantSplatVector(N0.getOperand(2).getNode(), ShlAmt) ||
         !ISD::isConstantSplatVector(N1.getOperand(2).getNode(), ShrAmt))
@@ -4570,11 +4588,11 @@ bool AArch64DAGToDAGISel::trySelectXAR(SDNode *N) {
     if (ShlAmt + ShrAmt != VT.getScalarSizeInBits())
       return false;
 
-    SDLoc DL(N);
+    SDLoc DLImm(N);
     SDValue Imm =
-        CurDAG->getTargetConstant(ShrAmt.getZExtValue(), DL, MVT::i32);
+        CurDAG->getTargetConstant(ShrAmt.getZExtValue(), DLImm, MVT::i32);
 
-    SDValue Ops[] = {XOR.getOperand(0), XOR.getOperand(1), Imm};
+    SDValue Ops[] = {R1, R2, Imm};
     if (auto Opc = SelectOpcodeFromVT<SelectTypeKind::Int>(
             VT, {AArch64::XAR_ZZZI_B, AArch64::XAR_ZZZI_H, AArch64::XAR_ZZZI_S,
                  AArch64::XAR_ZZZI_D})) {
@@ -4591,20 +4609,28 @@ bool AArch64DAGToDAGISel::trySelectXAR(SDNode *N) {
       N1->getOpcode() != AArch64ISD::VLSHR)
     return false;
 
-  if (N0->getOperand(0) != N1->getOperand(0) ||
-      N1->getOperand(0)->getOpcode() != ISD::XOR)
+  if (N0->getOperand(0) != N1->getOperand(0))
     return false;
 
-  SDValue XOR = N0.getOperand(0);
-  SDValue R1 = XOR.getOperand(0);
-  SDValue R2 = XOR.getOperand(1);
+  SDValue R1, R2;
+  if (N1->getOperand(0)->getOpcode() != ISD::XOR) {
+    SDValue Zero = CurDAG->getTargetConstant(0, DL, MVT::i64);
+    SDNode *MOV = CurDAG->getMachineNode(AArch64::MOVIv2d_ns, DL, VT, Zero);
+    SDValue MOVIV = SDValue(MOV, 0);
+    R1 = N1->getOperand(0);
+    R2 = MOVIV;
+  } else {
+    SDValue XOR = N0.getOperand(0);
+    R1 = XOR.getOperand(0);
+    R2 = XOR.getOperand(1);
+  }
 
   unsigned HsAmt = N0.getConstantOperandVal(1);
   unsigned ShAmt = N1.getConstantOperandVal(1);
 
-  SDLoc DL = SDLoc(N0.getOperand(1));
+  SDLoc DLImm = SDLoc(N0.getOperand(1));
   SDValue Imm = CurDAG->getTargetConstant(
-      ShAmt, DL, N0.getOperand(1).getValueType(), false);
+      ShAmt, DLImm, N0.getOperand(1).getValueType(), false);
 
   if (ShAmt + HsAmt != 64)
     return false;
diff --git a/llvm/test/CodeGen/AArch64/sve2-xar.ll b/llvm/test/CodeGen/AArch64/sve2-xar.ll
index e5a240b7a53fd..4d7b76ce985f9 100644
--- a/llvm/test/CodeGen/AArch64/sve2-xar.ll
+++ b/llvm/test/CodeGen/AArch64/sve2-xar.ll
@@ -170,13 +170,12 @@ define <vscale x 2 x i64> @xar_nxv2i64_l_neg1(<vscale x 2 x i64> %x, <vscale x 2
 ; OR instead of an XOR.
 ; TODO: We could use usra instruction here for SVE2.
 define <vscale x 2 x i64> @xar_nxv2i64_l_neg2(<vscale x 2 x i64> %x, <vscale x 2 x i64> %y) {
-; CHECK-LABEL: xar_nxv2i64_l_neg2:
-; CHECK:       // %bb.0:
-; CHECK-NEXT:    orr z0.d, z0.d, z1.d
-; CHECK-NEXT:    lsr z1.d, z0.d, #4
-; CHECK-NEXT:    lsl z0.d, z0.d, #60
-; CHECK-NEXT:    orr z0.d, z0.d, z1.d
-; CHECK-NEXT:    ret
+; SVE2-LABEL: xar_nxv2i64_l_neg2:
+; SVE2:       // %bb.0:
+; SVE2-NEXT:    movi v2.2d, #0000000000000000
+; SVE2-NEXT:    orr z0.d, z0.d, z1.d
+; SVE2-NEXT:    xar z0.d, z0.d, z2.d, #4
+; SVE2-NEXT:    ret
     %a = or <vscale x 2 x i64> %x, %y
     %b = call <vscale x 2 x i64> @llvm.fshl.nxv2i64(<vscale x 2 x i64> %a, <vscale x 2 x i64> %a, <vscale x 2 x i64> splat (i64 60))
     ret <vscale x 2 x i64> %b