Port FuncAddr & SymbolValue to ISLE (AArch64) (#4748)

Ported the existing implementations of the following opcodes for AArch64
to ISLE:
- `FuncAddr`
- `SymbolValue`

Copyright (c) 2022 Arm Limited

cranelift/codegen/src/isa/aarch64/inst.isle

@@ -2417,6 +2417,13 @@
             (_ Unit (emit (MInst.VecLoadReplicate dst src size flags))))
         dst))
 
+;; Helper for emitting `MInst.LoadExtName` instructions.
+(decl load_ext_name (BoxExternalName i64) Reg)
+(rule (load_ext_name extname offset)
+      (let ((dst WritableReg (temp_writable_reg $I64))
+            (_ Unit (emit (MInst.LoadExtName dst extname offset))))
+        dst))
+
 ;; Helper for emitting `MInst.LoadAddr` instructions.
 (decl load_addr (AMode) Reg)
 (rule (load_addr addr)

cranelift/codegen/src/isa/aarch64/lower.isle

@@ -1832,6 +1832,16 @@
 (rule (lower (debugtrap))
       (side_effect (brk)))
 
+;;;; Rules for `func_addr` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(rule (lower (func_addr (func_ref_data _ extname _)))
+      (load_ext_name (box_external_name extname) 0))
+
+;;;; Rules for `symbol_value` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(rule (lower (symbol_value (symbol_value_data extname _ offset)))
+      (load_ext_name (box_external_name extname) offset))
+
 ;;; Rules for `get_{frame,stack}_pointer` and `get_return_address` ;;;;;;;;;;;;;
 
 (rule (lower (get_frame_pointer))

cranelift/codegen/src/isa/aarch64/lower_inst.rs

@@ -569,31 +569,13 @@ pub(crate) fn lower_insn_to_regs(
             panic!("trapz / trapnz / resumable_trapnz should have been removed by legalization!");
         }
 
-        Opcode::FuncAddr => {
-            let rd = get_output_reg(ctx, outputs[0]).only_reg().unwrap();
-            let (extname, _) = ctx.call_target(insn).unwrap();
-            let extname = extname.clone();
-            ctx.emit(Inst::LoadExtName {
-                rd,
-                name: Box::new(extname),
-                offset: 0,
-            });
-        }
+        Opcode::FuncAddr => implemented_in_isle(ctx),
 
         Opcode::GlobalValue => {
             panic!("global_value should have been removed by legalization!");
         }
 
-        Opcode::SymbolValue => {
-            let rd = get_output_reg(ctx, outputs[0]).only_reg().unwrap();
-            let (extname, _, offset) = ctx.symbol_value(insn).unwrap();
-            let extname = extname.clone();
-            ctx.emit(Inst::LoadExtName {
-                rd,
-                name: Box::new(extname),
-                offset,
-            });
-        }
+        Opcode::SymbolValue => implemented_in_isle(ctx),
 
         Opcode::Call | Opcode::CallIndirect => {
             let caller_conv = ctx.abi().call_conv();