dialects (arm): add return instruction (bx lr) (#3521)

Add a return instruction which is equivalent to ```bx lr```

---------

Co-authored-by: emmau678 <eu233@Emma-laptop>

tests/filecheck/dialects/arm_func/test_ops.mlir

@@ -0,0 +1,9 @@
+// RUN: XDSL_ROUNDTRIP
+// RUN: XDSL_GENERIC_ROUNDTRIP
+// RUN: xdsl-opt -t arm-asm %s | filecheck %s --check-prefix=CHECK-ASM
+
+// CHECK: arm_func.return {"comment" = "this is a return instruction"}
+// CHECK-ASM: bx lr # this is a return instruction
+arm_func.return {"comment" = "this is a return instruction"}
+
+// CHECK-GENERIC: "arm_func.return"() {"comment" = "this is a return instruction"} : () -> ()

xdsl/dialects/__init__.py

@@ -38,6 +38,11 @@ def get_arm():
 
         return ARM
 
+    def get_arm_func():
+        from xdsl.dialects.arm_func import ARM_FUNC
+
+        return ARM_FUNC
+
     def get_bufferization():
         from xdsl.dialects.bufferization import Bufferization
 
@@ -335,6 +340,7 @@ def get_transform():
         "air": get_air,
         "arith": get_arith,
         "arm": get_arm,
+        "arm_func": get_arm_func,
         "bufferization": get_bufferization,
         "builtin": get_builtin,
         "cf": get_cf,

xdsl/dialects/arm_func.py

@@ -0,0 +1,51 @@
+from xdsl.dialects import arm
+from xdsl.dialects.builtin import StringAttr
+from xdsl.ir import Dialect
+from xdsl.irdl import (
+    irdl_op_definition,
+    traits_def,
+)
+from xdsl.traits import IsTerminator
+
+
+@irdl_op_definition
+class RetOp(arm.ops.ARMInstruction):
+    """
+    Return from subroutine.
+
+    Equivalent to `bx lr`
+    """
+
+    name = "arm_func.return"
+
+    assembly_format = "attr-dict"
+
+    traits = traits_def(IsTerminator())
+
+    def __init__(
+        self,
+        *,
+        comment: str | StringAttr | None = None,
+    ):
+        if isinstance(comment, str):
+            comment = StringAttr(comment)
+
+        super().__init__(
+            attributes={
+                "comment": comment,
+            },
+        )
+
+    def assembly_line_args(self):
+        return ()
+
+    def assembly_instruction_name(self) -> str:
+        return "bx lr"
+
+
+ARM_FUNC = Dialect(
+    "arm_func",
+    [
+        RetOp,
+    ],
+)