[AArch64][SVE] Allow basic use of target("aarch64.svcount") with +sve (#167875)

This prevents the backend from crashing for basic uses of __SVCount_t
type (e.g., as function arguments), without +sve2p1 or +sme2.
    
Fixes #167462

Author: MacDue

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -445,6 +445,9 @@ AArch64TargetLowering::AArch64TargetLowering(const TargetMachine &TM,
     addRegisterClass(MVT::nxv8i1, &AArch64::PPRRegClass);
     addRegisterClass(MVT::nxv16i1, &AArch64::PPRRegClass);
 
+    // Add sve predicate as counter type
+    addRegisterClass(MVT::aarch64svcount, &AArch64::PPRRegClass);
+
     // Add legal sve data types
     addRegisterClass(MVT::nxv16i8, &AArch64::ZPRRegClass);
     addRegisterClass(MVT::nxv8i16, &AArch64::ZPRRegClass);
@@ -473,15 +476,6 @@ AArch64TargetLowering::AArch64TargetLowering(const TargetMachine &TM,
     }
   }
 
-  if (Subtarget->hasSVE2p1() || Subtarget->hasSME2()) {
-    addRegisterClass(MVT::aarch64svcount, &AArch64::PPRRegClass);
-    setOperationPromotedToType(ISD::LOAD, MVT::aarch64svcount, MVT::nxv16i1);
-    setOperationPromotedToType(ISD::STORE, MVT::aarch64svcount, MVT::nxv16i1);
-
-    setOperationAction(ISD::SELECT, MVT::aarch64svcount, Custom);
-    setOperationAction(ISD::SELECT_CC, MVT::aarch64svcount, Expand);
-  }
-
   // Compute derived properties from the register classes
   computeRegisterProperties(Subtarget->getRegisterInfo());
 
@@ -1609,6 +1603,14 @@ AArch64TargetLowering::AArch64TargetLowering(const TargetMachine &TM,
            MVT::nxv4i16, MVT::nxv4i32, MVT::nxv8i8, MVT::nxv8i16 })
       setOperationAction(ISD::SIGN_EXTEND_INREG, VT, Legal);
 
+    // Promote predicate as counter load/stores to standard predicates.
+    setOperationPromotedToType(ISD::LOAD, MVT::aarch64svcount, MVT::nxv16i1);
+    setOperationPromotedToType(ISD::STORE, MVT::aarch64svcount, MVT::nxv16i1);
+
+    // Predicate as counter legalization actions.
+    setOperationAction(ISD::SELECT, MVT::aarch64svcount, Custom);
+    setOperationAction(ISD::SELECT_CC, MVT::aarch64svcount, Expand);
+
     for (auto VT :
          {MVT::nxv16i1, MVT::nxv8i1, MVT::nxv4i1, MVT::nxv2i1, MVT::nxv1i1}) {
       setOperationAction(ISD::CONCAT_VECTORS, VT, Custom);

llvm/test/CodeGen/AArch64/sme-aarch64-svcount.ll

@@ -1,6 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -O0 -mtriple=aarch64 -mattr=+sve2p1 < %s | FileCheck %s --check-prefixes=CHECK,CHECK-O0
-; RUN: llc -O3 -mtriple=aarch64 -mattr=+sve2p1 < %s | FileCheck %s --check-prefixes=CHECK,CHECK-O3
+; RUN: llc -O0 -mtriple=aarch64 -mattr=+sve < %s | FileCheck %s --check-prefixes=CHECK,CHECK-O0
+; RUN: llc -O3 -mtriple=aarch64 -mattr=+sve < %s | FileCheck %s --check-prefixes=CHECK,CHECK-O3
 
 ;
 ; Test simple loads, stores and return.