Introduce Undefined Value Graphs (UVGs) (#717)

broken_tests/other_errors/undefined_variable.jou

@@ -0,0 +1,29 @@
+import "stdlib/io.jou"
+
+@public
+def maybe_undefined(n: int) -> None:
+    for i = 0; i < n; i++:
+        message = "Hi"
+    puts(message)  # Warning: the value of 'message' may be undefined
+
+@public
+def surely_undefined_loop() -> None:
+    while False:
+        message = "Hi"  # Warning: this code will never run
+    puts(message)  # Warning: the value of 'message' is undefined
+
+@public
+def surely_undefined_annotation() -> None:
+    x: byte*
+    puts(x)  # Warning: the value of 'x' is undefined
+
+@public
+def surely_undefined_assignments() -> None:
+    a: int
+    b = &a
+    c = b
+    d = c
+    e = *d  # TODO: should emit warning, but this is too "advanced" for UVGs
+
+def main() -> int:
+    return 0

compiler/builders/ast_to_builder.jou

@@ -6,30 +6,44 @@ import "../errors_and_warnings.jou"
 import "../evaluate.jou"
 import "../types.jou"
 import "../types_in_ast.jou"
-import "./llvm_builder.jou"
+import "./either_builder.jou"
 
 
 class LocalVar:
     name: byte[100]
     # All local variables are represented as pointers to stack space, even
     # if they are never reassigned. LLVM will optimize the mess.
-    ptr: BuilderValue
+    ptr: EitherBuilderValue
 
 
 class Loop:
-    on_break: BuilderBlock
-    on_continue: BuilderBlock
+    on_break: EitherBuilderBlock
+    on_continue: EitherBuilderBlock
 
 
 class AstToBuilder:
-    builder: Builder*
+    builder: EitherBuilder*
     locals: LocalVar*
     nlocals: int
     loops: Loop*
     nloops: int
     returns_a_value: bool
 
-    def begin_function(self, sig: Signature*, locals: LocalVariable*, nlocals: int, public: bool) -> None:
+    location: Location
+
+    # Returns old location. Use it to restore the location when you're done.
+    def set_location(self, location: Location) -> Location:
+        old = self->location
+        self->location = location
+        # If no reasonable location is available (e.g. implicit return at end of function),
+        # continue using the previous location for now.
+        if location.path != NULL and location.lineno != 0:
+            self->builder->set_location(location)
+        return old
+
+    def begin_function(self, sig: Signature*, location: Location, locals: LocalVariable*, nlocals: int, public: bool) -> None:
+        old = self->set_location(location)
+
         # First n local variables are the arguments
         assert sig->nargs >= 0
         assert sig->nargs <= nlocals
@@ -45,7 +59,7 @@ class AstToBuilder:
         for i = 0; i < nlocals; i++:
             var_name = locals[i].name
             var_type = locals[i].type
-            var_ptr = self->builder->stack_alloc(var_type)
+            var_ptr = self->builder->stack_alloc(var_type, var_name)
             self->locals[i] = LocalVar{name = var_name, ptr = var_ptr}
             if i < sig->nargs:
                 # First n local variables are the function arguments
@@ -56,11 +70,10 @@ class AstToBuilder:
             jou_startup_sig = Signature{name = "_jou_startup"}
             self->builder->call(&jou_startup_sig, NULL, 0)
 
+        self->set_location(old)
+
     def end_function(self) -> None:
-        if self->returns_a_value:
-            self->builder->unreachable()
-        else:
-            self->builder->ret(NULL)  # implicit "return" when falling off end of function
+        self->builder->ret(NULL)  # implicit "return" when falling off end of function
         self->builder->end_function()
 
     def local_var_exists(self, name: byte*) -> bool:
@@ -69,27 +82,27 @@ class AstToBuilder:
                 return True
         return False
 
-    def local_var_ptr(self, name: byte*) -> BuilderValue:
+    def local_var_ptr(self, name: byte*) -> EitherBuilderValue:
         for i = 0; i < self->nlocals; i++:
             if strcmp(self->locals[i].name, name) == 0:
                 return self->locals[i].ptr
         assert False
 
-    def build_function_call(self, call: AstCall*) -> BuilderValue:
+    def build_function_call(self, call: AstCall*) -> EitherBuilderValue:
         assert call->method_call_self == NULL
 
         assert call->nargs <= 100
-        args: BuilderValue[100]
+        args: EitherBuilderValue[100]
         for i = 0; i < call->nargs; i++:
             args[i] = self->build_expression(&call->args[i])
         return self->builder->call(call->called_signature, args, call->nargs)
 
-    def build_method_call(self, call: AstCall*) -> BuilderValue:
+    def build_method_call(self, call: AstCall*) -> EitherBuilderValue:
         assert call->method_call_self != NULL
 
         # leave room for self
         assert call->nargs <= 99
-        args: BuilderValue[100]
+        args: EitherBuilderValue[100]
 
         k = 0
 
@@ -108,7 +121,7 @@ class AstToBuilder:
 
         return self->builder->call(call->called_signature, args, k)
 
-    def build_binop(self, op: AstExpressionKind, lhs: BuilderValue, rhs: BuilderValue) -> BuilderValue:
+    def build_binop(self, op: AstExpressionKind, lhs: EitherBuilderValue, rhs: EitherBuilderValue) -> EitherBuilderValue:
         match op:
             case AstExpressionKind.Eq:
                 return self->builder->eq(lhs, rhs)
@@ -142,11 +155,11 @@ class AstToBuilder:
         new_value = self->build_binop(op, old_value, rhs_value)
         self->builder->set_ptr(lhs_ptr, new_value)
 
-    def build_instantiation(self, class_type: Type*, inst: AstInstantiation*) -> BuilderValue:
+    def build_instantiation(self, class_type: Type*, inst: AstInstantiation*) -> EitherBuilderValue:
         assert class_type != NULL
         assert class_type->kind == TypeKind.Class
 
-        inst_ptr = self->builder->stack_alloc(class_type)
+        inst_ptr = self->builder->stack_alloc(class_type, NULL)
         self->builder->memset_to_zero(inst_ptr)
         for i = 0; i < inst->nfields; i++:
             field_ptr = self->builder->class_field_pointer(inst_ptr, inst->field_names[i])
@@ -155,7 +168,7 @@ class AstToBuilder:
 
         return self->builder->dereference(inst_ptr)
 
-    def build_and(self, lhsexpr: AstExpression*, rhsexpr: AstExpression*) -> BuilderValue:
+    def build_and(self, lhsexpr: AstExpression*, rhsexpr: AstExpression*) -> EitherBuilderValue:
         # Must be careful with side effects.
         #
         #    # lhs returning False means we don't evaluate rhs
@@ -166,7 +179,7 @@ class AstToBuilder:
         lhstrue = self->builder->add_block()
         lhsfalse = self->builder->add_block()
         done = self->builder->add_block()
-        resultptr = self->builder->stack_alloc(boolType)
+        resultptr = self->builder->stack_alloc(boolType, NULL)
 
         # if lhs:
         self->builder->branch(self->build_expression(lhsexpr), lhstrue, lhsfalse)
@@ -185,7 +198,7 @@ class AstToBuilder:
 
         return self->builder->dereference(resultptr)
 
-    def build_or(self, lhsexpr: AstExpression*, rhsexpr: AstExpression*) -> BuilderValue:
+    def build_or(self, lhsexpr: AstExpression*, rhsexpr: AstExpression*) -> EitherBuilderValue:
         # Must be careful with side effects.
         #
         #    # lhs returning True means we don't evaluate rhs
@@ -196,7 +209,7 @@ class AstToBuilder:
         lhstrue = self->builder->add_block()
         lhsfalse = self->builder->add_block()
         done = self->builder->add_block()
-        resultptr = self->builder->stack_alloc(boolType)
+        resultptr = self->builder->stack_alloc(boolType, NULL)
 
         # if lhs:
         self->builder->branch(self->build_expression(lhsexpr), lhstrue, lhsfalse)
@@ -215,7 +228,7 @@ class AstToBuilder:
 
         return self->builder->dereference(resultptr)
 
-    def build_increment_or_decrement(self, inner: AstExpression*, pre: bool, diff: int) -> BuilderValue:
+    def build_increment_or_decrement(self, inner: AstExpression*, pre: bool, diff: int) -> EitherBuilderValue:
         assert diff == 1 or diff == -1  # 1=increment, -1=decrement
 
         ptr = self->build_address_of_expression(inner)
@@ -234,11 +247,11 @@ class AstToBuilder:
         else:
             return old_value
 
-    def build_array(self, t: Type*, items: AstExpression*, nitems: int) -> BuilderValue:
+    def build_array(self, t: Type*, items: AstExpression*, nitems: int) -> EitherBuilderValue:
         assert t->kind == TypeKind.Array
         assert t->array.len == nitems
 
-        arr_ptr = self->builder->stack_alloc(t)
+        arr_ptr = self->builder->stack_alloc(t, NULL)
         first_item_ptr = self->builder->cast(arr_ptr, t->array.item_type->pointer_type())
 
         for i = 0; i < nitems; i++:
@@ -249,7 +262,7 @@ class AstToBuilder:
 
         return self->builder->dereference(arr_ptr)
 
-    def build_expression_without_implicit_cast(self, expr: AstExpression*) -> BuilderValue:
+    def build_expression_without_implicit_cast(self, expr: AstExpression*) -> EitherBuilderValue:
         match expr->kind:
             case AstExpressionKind.String:
                 if expr->types.orig_type == byteType->pointer_type():
@@ -309,7 +322,7 @@ class AstToBuilder:
                     # We need to copy, because it's not always possible to evaluate &foo.
                     # For example, consider evaluating some_function().some_field.
                     instance = self->build_expression(expr->class_field.instance)
-                    ptr = self->builder->stack_alloc(instance.type)
+                    ptr = self->builder->stack_alloc(expr->class_field.instance->types.implicit_cast_type, NULL)
                     self->builder->set_ptr(ptr, instance)
                 fieldptr = self->builder->class_field_pointer(ptr, expr->class_field.field_name)
                 return self->builder->dereference(fieldptr)
@@ -360,21 +373,28 @@ class AstToBuilder:
                 return self->builder->not_(self->build_expression(&expr->operands[0]))
         assert False
 
-    def build_expression(self, expr: AstExpression*) -> BuilderValue:
-        if expr->types.implicit_array_to_pointer_cast:
-            return self->builder->cast(self->build_address_of_expression(expr), expr->types.implicit_cast_type)
+    def build_expression(self, expr: AstExpression*) -> EitherBuilderValue:
+        old_location = self->set_location(expr->location)
 
-        raw = self->build_expression_without_implicit_cast(expr)
-        if expr->types.orig_type == NULL and expr->types.implicit_cast_type == NULL:
-            # Function/method call that returns no value
-            assert expr->kind == AstExpressionKind.Call
-            return BuilderValue{}
+        if expr->types.implicit_array_to_pointer_cast:
+            result = self->builder->cast(self->build_address_of_expression(expr), expr->types.implicit_cast_type)
         else:
-            assert expr->types.orig_type != NULL
-            assert expr->types.implicit_cast_type != NULL
-            return self->builder->cast(raw, expr->types.implicit_cast_type)
+            raw = self->build_expression_without_implicit_cast(expr)
+            if expr->types.orig_type == NULL and expr->types.implicit_cast_type == NULL:
+                # Function/method call that returns no value
+                assert expr->kind == AstExpressionKind.Call
+                result = EitherBuilderValue{}
+            else:
+                assert expr->types.orig_type != NULL
+                assert expr->types.implicit_cast_type != NULL
+                result = self->builder->cast(raw, expr->types.implicit_cast_type)
+
+        self->set_location(old_location)
+        return result
+
+    def build_address_of_expression(self, expr: AstExpression*) -> EitherBuilderValue:
+        old_location = self->set_location(expr->location)
 
-    def build_address_of_expression(self, expr: AstExpression*) -> BuilderValue:
         match expr->kind:
             case AstExpressionKind.GetClassField:
                 if expr->class_field.uses_arrow_operator:
@@ -383,25 +403,28 @@ class AstToBuilder:
                 else:
                     # &obj.field = &obj + memory offset
                     ptr = self->build_address_of_expression(expr->class_field.instance)
-                return self->builder->class_field_pointer(ptr, expr->class_field.field_name)
+                result = self->builder->class_field_pointer(ptr, expr->class_field.field_name)
             case AstExpressionKind.Self:
-                return self->local_var_ptr("self")
+                result = self->local_var_ptr("self")
             case AstExpressionKind.GetVariable:
                 if self->local_var_exists(expr->varname):
-                    return self->local_var_ptr(expr->varname)
+                    result = self->local_var_ptr(expr->varname)
                 else:
-                    return self->builder->global_var_ptr(expr->varname, expr->types.orig_type)
+                    result = self->builder->global_var_ptr(expr->varname, expr->types.orig_type)
             case AstExpressionKind.Indexing:
                 # &ptr[index] = ptr + memory offset
                 ptr = self->build_expression(&expr->operands[0])
                 index = self->build_expression(&expr->operands[1])
-                return self->builder->indexed_pointer(ptr, index)
+                result = self->builder->indexed_pointer(ptr, index)
             case AstExpressionKind.Dereference:
                 # &*ptr = ptr
-                return self->build_expression(&expr->operands[0])
+                result = self->build_expression(&expr->operands[0])
             case _:
                 assert False
 
+        self->set_location(old_location)
+        return result
+
     def build_if_statement(self, ifst: AstIfStatement*) -> None:
         done = self->builder->add_block()
         for i = 0; i < ifst->n_if_and_elifs; i++:
@@ -464,15 +487,15 @@ class AstToBuilder:
         done = self->builder->add_block()
         for i = 0; i < match_stmt->ncases; i++:
             then = self->builder->add_block()
-            otherwise = BuilderBlock{}  # will be replaced by loop below
+            otherwise = EitherBuilderBlock{}  # will be replaced by loop below
             for k = 0; k < match_stmt->cases[i].n_case_objs; k++:
                 case_obj = self->build_expression(&match_stmt->cases[i].case_objs[k])
                 if match_stmt->func_name[0] == '\0':
                     cond = self->builder->eq(match_obj, case_obj)
                 else:
                     args = [match_obj, case_obj]
                     func_ret = self->builder->call(&match_stmt->func_signature, args, 2)
-                    zero = self->builder->integer(func_ret.type, 0)
+                    zero = self->builder->integer(match_stmt->func_signature.returntype, 0)
                     cond = self->builder->eq(func_ret, zero)
                 otherwise = self->builder->add_block()
                 self->builder->branch(cond, then, otherwise)
@@ -519,6 +542,8 @@ class AstToBuilder:
         self->builder->set_current_block(ok_block)
 
     def build_statement(self, stmt: AstStatement*) -> None:
+        old_location = self->set_location(stmt->location)
+
         match stmt->kind:
             case AstStatementKind.If:
                 self->build_if_statement(&stmt->if_statement)
@@ -575,21 +600,23 @@ class AstToBuilder:
                 # other statements shouldn't occur inside functions/methods
                 assert False
 
+        self->set_location(old_location)
+
     def build_body(self, body: AstBody*) -> None:
         for i = 0; i < body->nstatements; i++:
             self->build_statement(&body->statements[i])
 
 
 @public
-def feed_ast_to_builder(ast: AstFunctionOrMethod*, builder: Builder*) -> None:
+def feed_ast_to_builder(func_ast: AstFunctionOrMethod*, func_location: Location, builder: EitherBuilder*) -> None:
     public = (
-        ast->public
-        or ast->types.signature.is_main_function()
-        or ast->types.signature.get_self_class() != NULL
+        func_ast->public
+        or func_ast->types.signature.is_main_function()
+        or func_ast->types.signature.get_self_class() != NULL
     )
     ast2ir = AstToBuilder{builder = builder}
-    ast2ir.begin_function(&ast->types.signature, ast->types.locals, ast->types.nlocals, public)
-    ast2ir.build_body(&ast->body)
+    ast2ir.begin_function(&func_ast->types.signature, func_location, func_ast->types.locals, func_ast->types.nlocals, public)
+    ast2ir.build_body(&func_ast->body)
     ast2ir.end_function()
     free(ast2ir.locals)
     free(ast2ir.loops)