[AArch64][SVE] Improve sve.convert.to.svbool lowering

The sve.convert.to.svbool lowering has the effect of widening a logical
<M x i1> vector representing lanes into a physical <16 x i1> vector
representing bits in a predicate register.

In general, if converting to svbool, the contents of lanes in the
physical register might not be known. For sve.convert.to.svbool the new
lanes are specified to be zeroed, requiring 'and' instructions to mask
off the new lanes. For lanes coming from a ptrue or a comparison,
however, they are known to be zero.

CodeGen Before:
  ptrue p0.s, vl16
  ptrue p1.s
  ptrue p2.b
  and   p0.b, p2/z, p0.b, p1.b
  ret

After:
  ptrue	p0.s, vl16
  ret

Differential Revision: https://reviews.llvm.org/D101544

lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -3690,6 +3690,37 @@ static inline SDValue getPTrue(SelectionDAG &DAG, SDLoc DL, EVT VT,
                      DAG.getTargetConstant(Pattern, DL, MVT::i32));
 }
 
+static SDValue lowerConvertToSVBool(SDValue Op, SelectionDAG &DAG) {
+  SDLoc DL(Op);
+  EVT OutVT = Op.getValueType();
+  SDValue InOp = Op.getOperand(1);
+  EVT InVT = InOp.getValueType();
+
+  // Return the operand if the cast isn't changing type,
+  // i.e. <n x 16 x i1> -> <n x 16 x i1>
+  if (InVT == OutVT)
+    return InOp;
+
+  SDValue Reinterpret =
+      DAG.getNode(AArch64ISD::REINTERPRET_CAST, DL, OutVT, InOp);
+
+  // If the argument converted to an svbool is a ptrue or a comparison, the
+  // lanes introduced by the widening are zero by construction.
+  switch (InOp.getOpcode()) {
+  case AArch64ISD::SETCC_MERGE_ZERO:
+    return Reinterpret;
+  case ISD::INTRINSIC_WO_CHAIN:
+    if (InOp.getConstantOperandVal(0) == Intrinsic::aarch64_sve_ptrue)
+      return Reinterpret;
+  }
+
+  // Otherwise, zero the newly introduced lanes.
+  SDValue Mask = getPTrue(DAG, DL, InVT, AArch64SVEPredPattern::all);
+  SDValue MaskReinterpret =
+      DAG.getNode(AArch64ISD::REINTERPRET_CAST, DL, OutVT, Mask);
+  return DAG.getNode(ISD::AND, DL, OutVT, Reinterpret, MaskReinterpret);
+}
+
 SDValue AArch64TargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
                                                      SelectionDAG &DAG) const {
   unsigned IntNo = cast<ConstantSDNode>(Op.getOperand(0))->getZExtValue();
@@ -3793,6 +3824,8 @@ SDValue AArch64TargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
   case Intrinsic::aarch64_sve_convert_from_svbool:
     return DAG.getNode(AArch64ISD::REINTERPRET_CAST, dl, Op.getValueType(),
                        Op.getOperand(1));
+  case Intrinsic::aarch64_sve_convert_to_svbool:
+    return lowerConvertToSVBool(Op, DAG);
   case Intrinsic::aarch64_sve_fneg:
     return DAG.getNode(AArch64ISD::FNEG_MERGE_PASSTHRU, dl, Op.getValueType(),
                        Op.getOperand(2), Op.getOperand(3), Op.getOperand(1));
@@ -3848,22 +3881,6 @@ SDValue AArch64TargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
   case Intrinsic::aarch64_sve_neg:
     return DAG.getNode(AArch64ISD::NEG_MERGE_PASSTHRU, dl, Op.getValueType(),
                        Op.getOperand(2), Op.getOperand(3), Op.getOperand(1));
-  case Intrinsic::aarch64_sve_convert_to_svbool: {
-    EVT OutVT = Op.getValueType();
-    EVT InVT = Op.getOperand(1).getValueType();
-    // Return the operand if the cast isn't changing type,
-    // i.e. <n x 16 x i1> -> <n x 16 x i1>
-    if (InVT == OutVT)
-      return Op.getOperand(1);
-    // Otherwise, zero the newly introduced lanes.
-    SDValue Reinterpret =
-        DAG.getNode(AArch64ISD::REINTERPRET_CAST, dl, OutVT, Op.getOperand(1));
-    SDValue Mask = getPTrue(DAG, dl, InVT, AArch64SVEPredPattern::all);
-    SDValue MaskReinterpret =
-        DAG.getNode(AArch64ISD::REINTERPRET_CAST, dl, OutVT, Mask);
-    return DAG.getNode(ISD::AND, dl, OutVT, Reinterpret, MaskReinterpret);
-  }
-
   case Intrinsic::aarch64_sve_insr: {
     SDValue Scalar = Op.getOperand(2);
     EVT ScalarTy = Scalar.getValueType();

test/CodeGen/AArch64/sve-intrinsics-reinterpret.ll

@@ -1,3 +1,4 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sve < %s | FileCheck %s
 
 ;
@@ -6,37 +7,41 @@
 
 define <vscale x 16 x i1> @reinterpret_bool_from_b(<vscale x 16 x i1> %pg) {
 ; CHECK-LABEL: reinterpret_bool_from_b:
-; CHECK: ret
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ret
   %out = call <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv16i1(<vscale x 16 x i1> %pg)
   ret <vscale x 16 x i1> %out
 }
 
 define <vscale x 16 x i1> @reinterpret_bool_from_h(<vscale x 8 x i1> %pg) {
 ; CHECK-LABEL: reinterpret_bool_from_h:
-; CHECK: ptrue p1.h
+; CHECK:       // %bb.0:
-; CHECK-NEXT: ptrue p2.b
+; CHECK-NEXT:    ptrue p1.h
-; CHECK-NEXT: and p0.b, p2/z, p0.b, p1.b
+; CHECK-NEXT:    ptrue p2.b
-; CHECK-NEXT: ret
+; CHECK-NEXT:    and p0.b, p2/z, p0.b, p1.b
+; CHECK-NEXT:    ret
   %out = call <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv8i1(<vscale x 8 x i1> %pg)
   ret <vscale x 16 x i1> %out
 }
 
 define <vscale x 16 x i1> @reinterpret_bool_from_s(<vscale x 4 x i1> %pg) {
 ; CHECK-LABEL: reinterpret_bool_from_s:
-; CHECK: ptrue p1.s
+; CHECK:       // %bb.0:
-; CHECK-NEXT: ptrue p2.b
+; CHECK-NEXT:    ptrue p1.s
-; CHECK-NEXT: and p0.b, p2/z, p0.b, p1.b
+; CHECK-NEXT:    ptrue p2.b
-; CHECK-NEXT: ret
+; CHECK-NEXT:    and p0.b, p2/z, p0.b, p1.b
+; CHECK-NEXT:    ret
   %out = call <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv4i1(<vscale x 4 x i1> %pg)
   ret <vscale x 16 x i1> %out
 }
 
 define <vscale x 16 x i1> @reinterpret_bool_from_d(<vscale x 2 x i1> %pg) {
 ; CHECK-LABEL: reinterpret_bool_from_d:
-; CHECK: ptrue p1.d
+; CHECK:       // %bb.0:
-; CHECK-NEXT: ptrue p2.b
+; CHECK-NEXT:    ptrue p1.d
-; CHECK-NEXT: and p0.b, p2/z, p0.b, p1.b
+; CHECK-NEXT:    ptrue p2.b
-; CHECK-NEXT: ret
+; CHECK-NEXT:    and p0.b, p2/z, p0.b, p1.b
+; CHECK-NEXT:    ret
   %out = call <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv2i1(<vscale x 2 x i1> %pg)
   ret <vscale x 16 x i1> %out
 }
@@ -47,32 +52,61 @@ define <vscale x 16 x i1> @reinterpret_bool_from_d(<vscale x 2 x i1> %pg) {
 
 define <vscale x 16 x i1> @reinterpret_bool_to_b(<vscale x 16 x i1> %pg) {
 ; CHECK-LABEL: reinterpret_bool_to_b:
-; CHECK: ret
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ret
   %out = call <vscale x 16 x i1> @llvm.aarch64.sve.convert.from.svbool.nxv16i1(<vscale x 16 x i1> %pg)
   ret <vscale x 16 x i1> %out
 }
 
 define <vscale x 8 x i1> @reinterpret_bool_to_h(<vscale x 16 x i1> %pg) {
 ; CHECK-LABEL: reinterpret_bool_to_h:
-; CHECK: ret
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ret
   %out = call <vscale x 8 x i1> @llvm.aarch64.sve.convert.from.svbool.nxv8i1(<vscale x 16 x i1> %pg)
   ret <vscale x 8 x i1> %out
 }
 
 define <vscale x 4 x i1> @reinterpret_bool_to_s(<vscale x 16 x i1> %pg) {
 ; CHECK-LABEL: reinterpret_bool_to_s:
-; CHECK: ret
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ret
   %out = call <vscale x 4 x i1> @llvm.aarch64.sve.convert.from.svbool.nxv4i1(<vscale x 16 x i1> %pg)
   ret <vscale x 4 x i1> %out
 }
 
 define <vscale x 2 x i1> @reinterpret_bool_to_d(<vscale x 16 x i1> %pg) {
 ; CHECK-LABEL: reinterpret_bool_to_d:
-; CHECK: ret
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ret
   %out = call <vscale x 2 x i1> @llvm.aarch64.sve.convert.from.svbool.nxv2i1(<vscale x 16 x i1> %pg)
   ret <vscale x 2 x i1> %out
 }
 
+; Reinterpreting a ptrue should not introduce an `and` instruction.
+define <vscale x 16 x i1> @reinterpret_ptrue() {
+; CHECK-LABEL: reinterpret_ptrue:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ptrue p0.h
+; CHECK-NEXT:    ret
+  %in = tail call <vscale x 8 x i1> @llvm.aarch64.sve.ptrue.nxv8i1(i32 31)
+  %out = tail call <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv8i1(<vscale x 8 x i1> %in)
+  ret <vscale x 16 x i1> %out
+}
+
+; Reinterpreting a comparison not introduce an `and` instruction.
+define <vscale x 16 x i1> @reinterpret_cmpgt(<vscale x 8 x i1> %p, <vscale x 8 x i16> %a, <vscale x 8 x i16> %b) {
+; CHECK-LABEL: reinterpret_cmpgt:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    cmpgt p0.h, p0/z, z0.h, z1.h
+; CHECK-NEXT:    ret
+  %1 = tail call <vscale x 8 x i1> @llvm.aarch64.sve.cmpgt.nxv8i16(<vscale x 8 x i1> %p, <vscale x 8 x i16> %a, <vscale x 8 x i16> %b)
+  %2 = tail call <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv8i1(<vscale x 8 x i1> %1)
+  ret <vscale x 16 x i1> %2
+}
+
+declare <vscale x 8 x i1> @llvm.aarch64.sve.ptrue.nxv8i1(i32 immarg)
+declare <vscale x 8 x i1> @llvm.aarch64.sve.cmpgt.nxv8i16(<vscale x 8 x i1>, <vscale x 8 x i16>, <vscale x 8 x i16>)
+
 declare <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv16i1(<vscale x 16 x i1>)
 declare <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv8i1(<vscale x 8 x i1>)
 declare <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv4i1(<vscale x 4 x i1>)