Port Fence, IsNull/IsInvalid & Debugtrap to ISLE (AArch64) (#4548)

Ported the existing implementation of the following Opcodes for AArch64
to ISLE:
- `Fence`
- `IsNull`
- `IsInvalid`
- `Debugtrap`

Copyright (c) 2022 Arm Limited

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

@@ -1567,6 +1567,27 @@
          (MInst.AluRRR (ALUOp.SubS) (operand_size ty) dst src1 src2)
          dst)))
 
+;; Helper for materializing a boolean value into a register from
+;; flags.
+(decl materialize_bool_result (u8 Cond) ConsumesFlags)
+(rule (materialize_bool_result 1 cond)
+      (let ((dst WritableReg (temp_writable_reg $I64)))
+        (ConsumesFlags.ConsumesFlagsReturnsReg
+         (MInst.CSet dst cond)
+         dst)))
+
+(rule -1 (materialize_bool_result _ty_bits cond)
+      (let ((dst WritableReg (temp_writable_reg $I64)))
+        (ConsumesFlags.ConsumesFlagsReturnsReg
+         (MInst.CSetm dst cond)
+         dst)))
+
+(decl cmn_imm (OperandSize Reg Imm12) ProducesFlags)
+(rule (cmn_imm size src1 src2)
+      (ProducesFlags.ProducesFlagsSideEffect
+       (MInst.AluRRImm12 (ALUOp.AddS) size (writable_zero_reg)
+        src1 src2)))
+
 (decl cmp_imm (OperandSize Reg Imm12) ProducesFlags)
 (rule (cmp_imm size src1 src2)
       (ProducesFlags.ProducesFlagsSideEffect

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

@@ -1699,3 +1699,29 @@
       (let ((low_half Reg (uqxtn x (lane_size ty)))
             (result Reg (uqxtn2 low_half y (lane_size ty))))
         result))
+
+;;;; Rules for `Fence` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(rule (lower (fence))
+      (let ((_ Unit (emit (MInst.Fence))))
+            (output_none)))
+
+;;;; Rules for `IsNull` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(rule (lower (has_type out_ty (is_null x @ (value_type ty))))
+      (with_flags (cmp_imm (operand_size ty) x (u8_into_imm12 0))
+                  (materialize_bool_result
+                   (ty_bits out_ty) (Cond.Eq))))
+
+;;;; Rules for `IsInvalid` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(rule (lower (has_type out_ty (is_invalid x @ (value_type ty))))
+      (with_flags (cmn_imm (operand_size ty) x (u8_into_imm12 1))
+                  (materialize_bool_result
+                   (ty_bits out_ty) (Cond.Eq))))
+
+;;;; Rules for `Debugtrap` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(rule (lower (debugtrap))
+      (let ((_ Unit (emit (MInst.Brk))))
+            (output_none)))

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

@@ -254,9 +254,7 @@ pub(crate) fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
 
         Opcode::AtomicStore => implemented_in_isle(ctx),
 
-        Opcode::Fence => {
-            ctx.emit(Inst::Fence {});
-        }
+        Opcode::Fence => implemented_in_isle(ctx),
 
         Opcode::StackLoad
         | Opcode::StackStore
@@ -399,34 +397,7 @@ pub(crate) fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
             materialize_bool_result(ctx, insn, rd, cond);
         }
 
-        Opcode::IsNull | Opcode::IsInvalid => {
-            // Null references are represented by the constant value 0; invalid references are
-            // represented by the constant value -1. See `define_reftypes()` in
-            // `meta/src/isa/x86/encodings.rs` to confirm.
-            let rd = get_output_reg(ctx, outputs[0]).only_reg().unwrap();
-            let rn = put_input_in_reg(ctx, inputs[0], NarrowValueMode::None);
-            let ty = ctx.input_ty(insn, 0);
-            let (alu_op, const_value) = match op {
-                Opcode::IsNull => {
-                    // cmp rn, #0
-                    (ALUOp::SubS, 0)
-                }
-                Opcode::IsInvalid => {
-                    // cmn rn, #1
-                    (ALUOp::AddS, 1)
-                }
-                _ => unreachable!(),
-            };
-            let const_value = ResultRSEImm12::Imm12(Imm12::maybe_from_u64(const_value).unwrap());
-            ctx.emit(alu_inst_imm12(
-                alu_op,
-                ty,
-                writable_zero_reg(),
-                rn,
-                const_value,
-            ));
-            materialize_bool_result(ctx, insn, rd, Cond::Eq);
-        }
+        Opcode::IsNull | Opcode::IsInvalid => implemented_in_isle(ctx),
 
         Opcode::Copy => {
             let rd = get_output_reg(ctx, outputs[0]).only_reg().unwrap();
@@ -546,9 +517,7 @@ pub(crate) fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
             }
         }
 
-        Opcode::Debugtrap => {
-            ctx.emit(Inst::Brk);
-        }
+        Opcode::Debugtrap => implemented_in_isle(ctx),
 
         Opcode::Trap | Opcode::ResumableTrap => implemented_in_isle(ctx),