[mypyc] Support ERR_ALWAYS (#9073)

Related to mypyc/mypyc#734, with a focus on exceptions related ops.

This PR adds a new error kind: ERR_ALWAYS, which indicates the op always fails.

It adds temporary false value to ensure such behavior in the exception handling
transform and makes the raise op void.

Author: TH3CHARLie

mypyc/codegen/emitfunc.py

@@ -130,15 +130,7 @@ def visit_branch(self, op: Branch) -> None:
 
         self.emit_line('if ({}) {{'.format(cond))
 
-        if op.traceback_entry is not None:
-            globals_static = self.emitter.static_name('globals', self.module_name)
-            self.emit_line('CPy_AddTraceback("%s", "%s", %d, %s);' % (
-                self.source_path.replace("\\", "\\\\"),
-                op.traceback_entry[0],
-                op.traceback_entry[1],
-                globals_static))
-            if DEBUG_ERRORS:
-                self.emit_line('assert(PyErr_Occurred() != NULL && "failure w/o err!");')
+        self.emit_traceback(op)
 
         self.emit_lines(
             'goto %s;' % self.label(op.true),
@@ -422,7 +414,10 @@ def visit_raise_standard_error(self, op: RaiseStandardError) -> None:
         self.emitter.emit_line('{} = 0;'.format(self.reg(op)))
 
     def visit_call_c(self, op: CallC) -> None:
-        dest = self.get_dest_assign(op)
+        if op.is_void:
+            dest = ''
+        else:
+            dest = self.get_dest_assign(op)
         args = ', '.join(self.reg(arg) for arg in op.args)
         self.emitter.emit_line("{}{}({});".format(dest, op.function_name, args))
 
@@ -472,3 +467,14 @@ def emit_dec_ref(self, dest: str, rtype: RType, is_xdec: bool) -> None:
 
     def emit_declaration(self, line: str) -> None:
         self.declarations.emit_line(line)
+
+    def emit_traceback(self, op: Branch) -> None:
+        if op.traceback_entry is not None:
+            globals_static = self.emitter.static_name('globals', self.module_name)
+            self.emit_line('CPy_AddTraceback("%s", "%s", %d, %s);' % (
+                self.source_path.replace("\\", "\\\\"),
+                op.traceback_entry[0],
+                op.traceback_entry[1],
+                globals_static))
+            if DEBUG_ERRORS:
+                self.emit_line('assert(PyErr_Occurred() != NULL && "failure w/o err!");')

mypyc/ir/ops.py

@@ -295,6 +295,8 @@ def terminated(self) -> bool:
 ERR_FALSE = 2  # type: Final
 # Generates negative integer on exception
 ERR_NEG_INT = 3  # type: Final
+# Always fails
+ERR_ALWAYS = 4  # type: Final
 
 # Hack: using this line number for an op will suppress it in tracebacks
 NO_TRACEBACK_LINE_NO = -10000
@@ -1167,7 +1169,10 @@ def __init__(self,
 
     def to_str(self, env: Environment) -> str:
         args_str = ', '.join(env.format('%r', arg) for arg in self.args)
-        return env.format('%r = %s(%s)', self, self.function_name, args_str)
+        if self.is_void:
+            return env.format('%s(%s)', self.function_name, args_str)
+        else:
+            return env.format('%r = %s(%s)', self, self.function_name, args_str)
 
     def sources(self) -> List[Value]:
         return self.args

mypyc/irbuild/statement.py

@@ -243,7 +243,7 @@ def transform_raise_stmt(builder: IRBuilder, s: RaiseStmt) -> None:
         return
 
     exc = builder.accept(s.expr)
-    builder.primitive_op(raise_exception_op, [exc], s.line)
+    builder.call_c(raise_exception_op, [exc], s.line)
     builder.add(Unreachable())
 
 
@@ -614,7 +614,7 @@ def transform_assert_stmt(builder: IRBuilder, a: AssertStmt) -> None:
         message = builder.accept(a.msg)
         exc_type = builder.load_module_attr_by_fullname('builtins.AssertionError', a.line)
         exc = builder.py_call(exc_type, [message], a.line)
-        builder.primitive_op(raise_exception_op, [exc], a.line)
+        builder.call_c(raise_exception_op, [exc], a.line)
     builder.add(Unreachable())
     builder.activate_block(ok_block)
 

mypyc/primitives/exc_ops.py

@@ -1,21 +1,18 @@
 """Exception-related primitive ops."""
 
-from mypyc.ir.ops import ERR_NEVER, ERR_FALSE
+from mypyc.ir.ops import ERR_NEVER, ERR_FALSE, ERR_ALWAYS
 from mypyc.ir.rtypes import bool_rprimitive, object_rprimitive, void_rtype, exc_rtuple
 from mypyc.primitives.registry import (
-    simple_emit, call_emit, call_void_emit, call_and_fail_emit, custom_op,
+    simple_emit, call_emit, call_void_emit, call_and_fail_emit, custom_op, c_custom_op
 )
 
 # If the argument is a class, raise an instance of the class. Otherwise, assume
 # that the argument is an exception object, and raise it.
-#
-# TODO: Making this raise conditionally is kind of hokey.
-raise_exception_op = custom_op(
+raise_exception_op = c_custom_op(
     arg_types=[object_rprimitive],
-    result_type=bool_rprimitive,
-    error_kind=ERR_FALSE,
-    format_str='raise_exception({args[0]}); {dest} = 0',
-    emit=call_and_fail_emit('CPy_Raise'))
+    return_type=void_rtype,
+    c_function_name='CPy_Raise',
+    error_kind=ERR_ALWAYS)
 
 # Raise StopIteration exception with the specified value (which can be NULL).
 set_stop_iteration_value = custom_op(

mypyc/test-data/irbuild-basic.test

@@ -1322,24 +1322,22 @@ def foo():
     r0 :: object
     r1 :: str
     r2, r3 :: object
-    r4 :: bool
 L0:
     r0 = builtins :: module
     r1 = unicode_1 :: static  ('Exception')
     r2 = getattr r0, r1
     r3 = py_call(r2)
-    raise_exception(r3); r4 = 0
+    CPy_Raise(r3)
     unreachable
 def bar():
     r0 :: object
     r1 :: str
     r2 :: object
-    r3 :: bool
 L0:
     r0 = builtins :: module
     r1 = unicode_1 :: static  ('Exception')
     r2 = getattr r0, r1
-    raise_exception(r2); r3 = 0
+    CPy_Raise(r2)
     unreachable
 
 [case testModuleTopLevel_toplevel]

mypyc/test-data/irbuild-statements.test

@@ -614,8 +614,7 @@ def complex_msg(x, s):
     r4 :: object
     r5 :: str
     r6, r7 :: object
-    r8 :: bool
-    r9 :: None
+    r8 :: None
 L0:
     r0 = builtins.None :: object
     r1 = x is not r0
@@ -629,11 +628,11 @@ L2:
     r5 = unicode_3 :: static  ('AssertionError')
     r6 = getattr r4, r5
     r7 = py_call(r6, s)
-    raise_exception(r7); r8 = 0
+    CPy_Raise(r7)
     unreachable
 L3:
-    r9 = None
-    return r9
+    r8 = None
+    return r8
 
 [case testDelList]
 def delList() -> None:

mypyc/test-data/irbuild-try.test

@@ -277,14 +277,13 @@ def a(b):
     r1 :: object
     r2 :: str
     r3, r4 :: object
-    r5 :: bool
-    r6, r7, r8 :: tuple[object, object, object]
-    r9 :: str
-    r10 :: object
-    r11 :: str
-    r12, r13 :: object
-    r14, r15 :: bool
-    r16 :: None
+    r5, r6, r7 :: tuple[object, object, object]
+    r8 :: str
+    r9 :: object
+    r10 :: str
+    r11, r12 :: object
+    r13, r14 :: bool
+    r15 :: None
 L0:
 L1:
     if b goto L2 else goto L3 :: bool
@@ -294,39 +293,39 @@ L2:
     r2 = unicode_2 :: static  ('Exception')
     r3 = getattr r1, r2
     r4 = py_call(r3, r0)
-    raise_exception(r4); r5 = 0
+    CPy_Raise(r4)
     unreachable
 L3:
 L4:
 L5:
-    r7 = <error> :: tuple[object, object, object]
-    r6 = r7
+    r6 = <error> :: tuple[object, object, object]
+    r5 = r6
     goto L7
 L6: (handler for L1, L2, L3)
-    r8 = error_catch
-    r6 = r8
+    r7 = error_catch
+    r5 = r7
 L7:
-    r9 = unicode_3 :: static  ('finally')
-    r10 = builtins :: module
-    r11 = unicode_4 :: static  ('print')
-    r12 = getattr r10, r11
-    r13 = py_call(r12, r9)
-    if is_error(r6) goto L9 else goto L8
+    r8 = unicode_3 :: static  ('finally')
+    r9 = builtins :: module
+    r10 = unicode_4 :: static  ('print')
+    r11 = getattr r9, r10
+    r12 = py_call(r11, r8)
+    if is_error(r5) goto L9 else goto L8
 L8:
-    reraise_exc; r14 = 0
+    reraise_exc; r13 = 0
     unreachable
 L9:
     goto L13
 L10: (handler for L7, L8)
-    if is_error(r6) goto L12 else goto L11
+    if is_error(r5) goto L12 else goto L11
 L11:
-    restore_exc_info r6
+    restore_exc_info r5
 L12:
-    r15 = keep_propagating
+    r14 = keep_propagating
     unreachable
 L13:
-    r16 = None
-    return r16
+    r15 = None
+    return r15
 
 [case testWith]
 from typing import Any

mypyc/transform/exceptions.py

@@ -12,10 +12,11 @@
 from typing import List, Optional
 
 from mypyc.ir.ops import (
-    BasicBlock, LoadErrorValue, Return, Branch, RegisterOp, ERR_NEVER, ERR_MAGIC,
-    ERR_FALSE, ERR_NEG_INT, NO_TRACEBACK_LINE_NO,
+    BasicBlock, LoadErrorValue, Return, Branch, RegisterOp, LoadInt, ERR_NEVER, ERR_MAGIC,
+    ERR_FALSE, ERR_NEG_INT, ERR_ALWAYS, NO_TRACEBACK_LINE_NO, Environment
 )
 from mypyc.ir.func_ir import FuncIR
+from mypyc.ir.rtypes import bool_rprimitive
 
 
 def insert_exception_handling(ir: FuncIR) -> None:
@@ -29,7 +30,7 @@ def insert_exception_handling(ir: FuncIR) -> None:
             error_label = add_handler_block(ir)
             break
     if error_label:
-        ir.blocks = split_blocks_at_errors(ir.blocks, error_label, ir.traceback_name)
+        ir.blocks = split_blocks_at_errors(ir.blocks, error_label, ir.traceback_name, ir.env)
 
 
 def add_handler_block(ir: FuncIR) -> BasicBlock:
@@ -44,7 +45,8 @@ def add_handler_block(ir: FuncIR) -> BasicBlock:
 
 def split_blocks_at_errors(blocks: List[BasicBlock],
                            default_error_handler: BasicBlock,
-                           func_name: Optional[str]) -> List[BasicBlock]:
+                           func_name: Optional[str],
+                           env: Environment) -> List[BasicBlock]:
     new_blocks = []  # type: List[BasicBlock]
 
     # First split blocks on ops that may raise.
@@ -60,6 +62,7 @@ def split_blocks_at_errors(blocks: List[BasicBlock],
         block.error_handler = None
 
         for op in ops:
+            target = op
             cur_block.ops.append(op)
             if isinstance(op, RegisterOp) and op.error_kind != ERR_NEVER:
                 # Split
@@ -77,14 +80,24 @@ def split_blocks_at_errors(blocks: List[BasicBlock],
                 elif op.error_kind == ERR_NEG_INT:
                     variant = Branch.NEG_INT_EXPR
                     negated = False
+                elif op.error_kind == ERR_ALWAYS:
+                    variant = Branch.BOOL_EXPR
+                    negated = True
+                    # this is a hack to represent the always fail
+                    # semantics, using a temporary bool with value false
+                    tmp = LoadInt(0, rtype=bool_rprimitive)
+                    cur_block.ops.append(tmp)
+                    env.add_op(tmp)
+                    target = tmp
                 else:
                     assert False, 'unknown error kind %d' % op.error_kind
 
                 # Void ops can't generate errors since error is always
                 # indicated by a special value stored in a register.
-                assert not op.is_void, "void op generating errors?"
+                if op.error_kind != ERR_ALWAYS:
+                    assert not op.is_void, "void op generating errors?"
 
-                branch = Branch(op,
+                branch = Branch(target,
                                 true_label=error_label,
                                 false_label=new_block,
                                 op=variant,