[CIR][NFC] Add infrastructure for AArch64 builtins (llvm#170386)

This change adds the basic code structure for handling AArch64 builtins.
The structure of this code is brought over from classic codegen to make
implementing missing builtins easier. In some cases, the handling
involved too much logic for a simple NFC change, so those parts were
replaced with a MissingFeature assert.

The actual handling for all builtins is left for later changes.

Author: andykaylor

clang/include/clang/CIR/MissingFeatures.h

@@ -190,6 +190,10 @@ struct MissingFeatures {
   static bool globalCtorAssociatedData() { return false; }
 
   // Misc
+  static bool aarch64SIMDIntrinsics() { return false; }
+  static bool aarch64SMEIntrinsics() { return false; }
+  static bool aarch64SVEIntrinsics() { return false; }
+  static bool aarch64TblBuiltinExpr() { return false; }
   static bool abiArgInfo() { return false; }
   static bool addAutoInitAnnotation() { return false; }
   static bool addHeapAllocSiteMetadata() { return false; }
@@ -293,6 +297,7 @@ struct MissingFeatures {
   static bool metaDataNode() { return false; }
   static bool moduleNameHash() { return false; }
   static bool msabi() { return false; }
+  static bool neonSISDIntrinsics() { return false; }
   static bool nrvo() { return false; }
   static bool objCBlocks() { return false; }
   static bool objCGC() { return false; }

clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp

@@ -1361,9 +1361,13 @@ static mlir::Value emitTargetArchBuiltinExpr(CIRGenFunction *cgf,
   case llvm::Triple::armeb:
   case llvm::Triple::thumb:
   case llvm::Triple::thumbeb:
+    // These are actually NYI, but that will be reported by emitBuiltinExpr.
+    // At this point, we don't even know that the builtin is target-specific.
+    return nullptr;
   case llvm::Triple::aarch64:
   case llvm::Triple::aarch64_32:
   case llvm::Triple::aarch64_be:
+    return cgf->emitAArch64BuiltinExpr(builtinID, e, returnValue, arch);
   case llvm::Triple::bpfeb:
   case llvm::Triple::bpfel:
     // These are actually NYI, but that will be reported by emitBuiltinExpr.