Dl/scf lowering miss yield (#487)

Fixes issue #468

Author: zhenrongliew

src/kirin/dialects/scf/lowering.py

@@ -45,12 +45,27 @@ def lower_If(self, state: lowering.State, node: ast.If) -> lowering.Result:
         yield_names: list[str] = []
         body_yields: list[ir.SSAValue] = []
         else_yields: list[ir.SSAValue] = []
-        for name in body_frame.defs.keys():
-            if name in else_frame.defs:
+        all_names: set[str] = set(body_frame.defs.keys()) | (
+            set(else_frame.defs.keys())
+        )
+        for name in all_names:
+            if name in body_frame.defs and name in else_frame.defs:
                 yield_names.append(name)
                 body_yields.append(body_frame[name])
                 else_yields.append(else_frame[name])
-            elif (value := self._frame_or_any_parent_has_def(frame, name)) is not None:
+            elif (
+                name not in body_frame.defs
+                and (value := self._frame_or_any_parent_has_def(frame, name))
+                is not None
+            ):
+                yield_names.append(name)
+                body_yields.append(value)
+                else_yields.append(else_frame[name])
+            elif (
+                name not in else_frame.defs
+                and (value := self._frame_or_any_parent_has_def(frame, name))
+                is not None
+            ):
                 yield_names.append(name)
                 body_yields.append(body_frame[name])
                 else_yields.append(value)

test/dialects/scf/test_ifelse.py

@@ -110,3 +110,38 @@ def main_nested_if(n: int):
 
     assert main_nested_if(3) == 4 == main_nested_if2(3)
     assert main_nested_if(10) == 0 == main_nested_if2(8)
+
+
+def test_def_only_else():
+    @kernel
+    def main(n: int):
+        c = 1.0
+        if n <= 0:
+            return 0.0
+        else:
+            c = 2.0
+        return c
+
+    main.print()
+    assert main(1) == 2.0
+    assert main(0) == 0.0
+
+
+def test_def_only_else_nested():
+    @kernel
+    def main(n: int):
+        c = 1.0
+        if n <= 0:
+            return 0.0
+        else:
+            if n <= 2:
+                return 1.0
+            else:
+                c = 4.0
+        return c
+
+    main.print()
+    assert main(3) == 4.0
+    assert main(2) == 1.0
+    assert main(1) == 1.0
+    assert main(0) == 0.0