[GlobalISel][AArch64] Handles bitreverse to prevent falling back (#138150)

Handles bitreverse for vector types which were previously falling back
onto Selection DAG. Includes 8-bit element vectors greater than 128 bits
and less than 64 bits: <32 x i8>, <4 x i8>, and odd vector types: <9 x
i8>.

Author: jyli0116

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -6136,6 +6136,7 @@ LegalizerHelper::moreElementsVector(MachineInstr &MI, unsigned TypeIdx,
   case TargetOpcode::G_INTRINSIC_ROUND:
   case TargetOpcode::G_INTRINSIC_ROUNDEVEN:
   case TargetOpcode::G_INTRINSIC_TRUNC:
+  case TargetOpcode::G_BITREVERSE:
   case TargetOpcode::G_BSWAP:
   case TargetOpcode::G_FCANONICALIZE:
   case TargetOpcode::G_SEXT_INREG:

llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp

@@ -366,6 +366,8 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
       .legalFor({s32, s64, v8s8, v16s8})
       .widenScalarToNextPow2(0, /*Min = */ 32)
       .clampScalar(0, s32, s64)
+      .clampNumElements(0, v8s8, v16s8)
+      .moreElementsToNextPow2(0)
       .lower();
 
   getActionDefinitionsBuilder(G_BSWAP)

llvm/test/CodeGen/AArch64/bitreverse.ll

@@ -136,6 +136,50 @@ define <16 x i8> @g_vec_16x8(<16 x i8> %a) {
   ret <16 x i8> %b
 }
 
+declare <32 x i8> @llvm.bitreverse.v32i8(<32 x i8>) readnone
+
+define <32 x i8> @g_vec_32x8(<32 x i8> %a) {
+; CHECK-LABEL: g_vec_32x8:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    rbit v0.16b, v0.16b
+; CHECK-NEXT:    rbit v1.16b, v1.16b
+; CHECK-NEXT:    ret
+  %b = call <32 x i8> @llvm.bitreverse.v32i8(<32 x i8> %a)
+  ret <32 x i8> %b
+}
+
+declare <4 x i8> @llvm.bitreverse.v4i8(<4 x i8>) readnone
+
+define <4 x i8> @g_vec_4x8(<4 x i8> %a) {
+; SDAG-LABEL: g_vec_4x8:
+; SDAG:       // %bb.0:
+; SDAG-NEXT:    rev16 v0.8b, v0.8b
+; SDAG-NEXT:    rbit v0.8b, v0.8b
+; SDAG-NEXT:    ushr v0.4h, v0.4h, #8
+; SDAG-NEXT:    ret
+;
+; GISEL-LABEL: g_vec_4x8:
+; GISEL:       // %bb.0:
+; GISEL-NEXT:    uzp1 v0.8b, v0.8b, v0.8b
+; GISEL-NEXT:    rbit v0.8b, v0.8b
+; GISEL-NEXT:    ushll v0.8h, v0.8b, #0
+; GISEL-NEXT:    // kill: def $d0 killed $d0 killed $q0
+; GISEL-NEXT:    ret
+  %b = call <4 x i8> @llvm.bitreverse.v4i8(<4 x i8> %a)
+  ret <4 x i8> %b
+}
+
+declare <9 x i8> @llvm.bitreverse.v9i8(<9 x i8>) readnone
+
+define <9 x i8> @g_vec_9x8(<9 x i8> %a) {
+; CHECK-LABEL: g_vec_9x8:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    rbit v0.16b, v0.16b
+; CHECK-NEXT:    ret
+  %b = call <9 x i8> @llvm.bitreverse.v9i8(<9 x i8> %a)
+  ret <9 x i8> %b
+}
+
 declare <4 x i16> @llvm.bitreverse.v4i16(<4 x i16>) readnone
 
 define <4 x i16> @g_vec_4x16(<4 x i16> %a) {