/* Return true if the conversion from INNER_TYPE to OUTER_TYPE is a
- useless type conversion, otherwise return false. */
+ useless type conversion, otherwise return false.
+
+ This function implicitly defines the middle-end type system. With
+ the notion of 'a < b' meaning that useless_type_conversion_p (a, b)
+ holds and 'a > b' meaning that useless_type_conversion_p (b, a) holds,
+ the following invariants shall be fulfilled:
+
+ 1) useless_type_conversion_p is transitive.
+ If a < b and b < c then a < c.
+
+ 2) useless_type_conversion_p is not symmetric.
+ From a < b does not follow a > b.
+
+ 3) Types define the available set of operations applicable to values.
+ A type conversion is useless if the operations for the target type
+ is a subset of the operations for the source type. For example
+ casts to void* are useless, casts from void* are not (void* can't
+ be dereferenced or offsetted, but copied, hence its set of operations
+ is a strict subset of that of all other data pointer types). Casts
+ to const T* are useless (can't be written to), casts from const T*
+ to T* are not. */
bool
useless_type_conversion_p (tree outer_type, tree inner_type)
{
+ /* Qualifiers on value types do not matter. */
+ inner_type = TYPE_MAIN_VARIANT (inner_type);
+ outer_type = TYPE_MAIN_VARIANT (outer_type);
+
if (inner_type == outer_type)
return true;
+ /* If we know the canonical types, compare them. */
+ if (TYPE_CANONICAL (inner_type)
+ && TYPE_CANONICAL (inner_type) == TYPE_CANONICAL (outer_type))
+ return true;
+
/* Changes in machine mode are never useless conversions. */
if (TYPE_MODE (inner_type) != TYPE_MODE (outer_type))
return false;
- /* If the inner and outer types are effectively the same, then
- strip the type conversion and enter the equivalence into
- the table. */
- if (lang_hooks.types_compatible_p (inner_type, outer_type))
- return true;
-
- /* If both types are pointers and the outer type is a (void *), then
- the conversion is not necessary. The opposite is not true since
- that conversion would result in a loss of information if the
- equivalence was used. Consider an indirect function call where
- we need to know the exact type of the function to correctly
- implement the ABI. */
- else if (POINTER_TYPE_P (inner_type)
- && POINTER_TYPE_P (outer_type)
- && TYPE_REF_CAN_ALIAS_ALL (inner_type)
- == TYPE_REF_CAN_ALIAS_ALL (outer_type)
- && TREE_CODE (TREE_TYPE (outer_type)) == VOID_TYPE)
- return true;
+ /* If both the inner and outer types are integral types, then the
+ conversion is not necessary if they have the same mode and
+ signedness and precision, and both or neither are boolean. */
+ if (INTEGRAL_TYPE_P (inner_type)
+ && INTEGRAL_TYPE_P (outer_type))
+ {
+ /* Preserve changes in signedness or precision. */
+ if (TYPE_UNSIGNED (inner_type) != TYPE_UNSIGNED (outer_type)
+ || TYPE_PRECISION (inner_type) != TYPE_PRECISION (outer_type))
+ return false;
+
+ /* Conversions from a non-base to a base type are not useless.
+ This way we preserve the invariant to do arithmetic in
+ base types only. */
+ if (TREE_TYPE (inner_type)
+ && TREE_TYPE (inner_type) != inner_type
+ && (TREE_TYPE (outer_type) == outer_type
+ || TREE_TYPE (outer_type) == NULL_TREE))
+ return false;
+
+ /* We don't need to preserve changes in the types minimum or
+ maximum value in general as these do not generate code
+ unless the types precisions are different. */
- /* Don't lose casts between pointers to volatile and non-volatile
- qualified types. Doing so would result in changing the semantics
- of later accesses. */
- else if (POINTER_TYPE_P (inner_type)
- && POINTER_TYPE_P (outer_type)
- && TYPE_VOLATILE (TREE_TYPE (outer_type))
- != TYPE_VOLATILE (TREE_TYPE (inner_type)))
- return false;
+ return true;
+ }
- /* Pointers/references are equivalent if their pointed to types
- are effectively the same. This allows to strip conversions between
- pointer types with different type qualifiers. */
- else if (POINTER_TYPE_P (inner_type)
- && POINTER_TYPE_P (outer_type)
- && TYPE_REF_CAN_ALIAS_ALL (inner_type)
- == TYPE_REF_CAN_ALIAS_ALL (outer_type)
- && lang_hooks.types_compatible_p (TREE_TYPE (inner_type),
- TREE_TYPE (outer_type)))
+ /* Scalar floating point types with the same mode are compatible. */
+ else if (SCALAR_FLOAT_TYPE_P (inner_type)
+ && SCALAR_FLOAT_TYPE_P (outer_type))
return true;
- /* If both the inner and outer types are integral types, then the
- conversion is not necessary if they have the same mode and
- signedness and precision, and both or neither are boolean. Some
- code assumes an invariant that boolean types stay boolean and do
- not become 1-bit bit-field types. Note that types with precision
- not using all bits of the mode (such as bit-field types in C)
- mean that testing of precision is necessary. */
- else if (INTEGRAL_TYPE_P (inner_type)
- && INTEGRAL_TYPE_P (outer_type)
- && TYPE_UNSIGNED (inner_type) == TYPE_UNSIGNED (outer_type)
- && TYPE_PRECISION (inner_type) == TYPE_PRECISION (outer_type))
+ /* We need to take special care recursing to pointed-to types. */
+ else if (POINTER_TYPE_P (inner_type)
+ && POINTER_TYPE_P (outer_type))
{
- tree min_inner = fold_convert (outer_type, TYPE_MIN_VALUE (inner_type));
- tree max_inner = fold_convert (outer_type, TYPE_MAX_VALUE (inner_type));
- bool first_boolean = (TREE_CODE (inner_type) == BOOLEAN_TYPE);
- bool second_boolean = (TREE_CODE (outer_type) == BOOLEAN_TYPE);
- if (simple_cst_equal (max_inner, TYPE_MAX_VALUE (outer_type))
- && simple_cst_equal (min_inner, TYPE_MIN_VALUE (outer_type))
- && first_boolean == second_boolean)
+ /* If the outer type is (void *), then the conversion is not
+ necessary. */
+ if (TREE_CODE (TREE_TYPE (outer_type)) == VOID_TYPE)
return true;
+
+ /* Don't lose casts between pointers to volatile and non-volatile
+ qualified types. Doing so would result in changing the semantics
+ of later accesses. */
+ if ((TYPE_VOLATILE (TREE_TYPE (outer_type))
+ != TYPE_VOLATILE (TREE_TYPE (inner_type)))
+ && TYPE_VOLATILE (TREE_TYPE (outer_type)))
+ return false;
+
+ /* Do not lose casts between pointers with different
+ TYPE_REF_CAN_ALIAS_ALL setting or alias sets. */
+ if ((TYPE_REF_CAN_ALIAS_ALL (inner_type)
+ != TYPE_REF_CAN_ALIAS_ALL (outer_type))
+ || (get_alias_set (TREE_TYPE (inner_type))
+ != get_alias_set (TREE_TYPE (outer_type))))
+ return false;
+
+ /* Do not lose casts from const qualified to non-const
+ qualified. */
+ if ((TYPE_READONLY (TREE_TYPE (outer_type))
+ != TYPE_READONLY (TREE_TYPE (inner_type)))
+ && TYPE_READONLY (TREE_TYPE (inner_type)))
+ return false;
+
+ /* Do not lose casts to restrict qualified pointers. */
+ if ((TYPE_RESTRICT (outer_type)
+ != TYPE_RESTRICT (inner_type))
+ && TYPE_RESTRICT (outer_type))
+ return false;
+
+ /* Otherwise pointers/references are equivalent if their pointed
+ to types are effectively the same. We can strip qualifiers
+ on pointed-to types for further comparison, which is done in
+ the callee. */
+ return useless_type_conversion_p (TREE_TYPE (outer_type),
+ TREE_TYPE (inner_type));
}
/* Recurse for complex types. */
else if (TREE_CODE (inner_type) == COMPLEX_TYPE
- && TREE_CODE (outer_type) == COMPLEX_TYPE
- && useless_type_conversion_p (TREE_TYPE (outer_type),
- TREE_TYPE (inner_type)))
- return true;
+ && TREE_CODE (outer_type) == COMPLEX_TYPE)
+ return useless_type_conversion_p (TREE_TYPE (outer_type),
+ TREE_TYPE (inner_type));
+
+ /* Recurse for vector types with the same number of subparts. */
+ else if (TREE_CODE (inner_type) == VECTOR_TYPE
+ && TREE_CODE (outer_type) == VECTOR_TYPE
+ && TYPE_PRECISION (inner_type) == TYPE_PRECISION (outer_type))
+ return useless_type_conversion_p (TREE_TYPE (outer_type),
+ TREE_TYPE (inner_type));
+
+ /* For aggregates we may need to fall back to structural equality
+ checks. */
+ else if (AGGREGATE_TYPE_P (inner_type)
+ && AGGREGATE_TYPE_P (outer_type))
+ {
+ /* Different types of aggregates are incompatible. */
+ if (TREE_CODE (inner_type) != TREE_CODE (outer_type))
+ return false;
+
+ /* ??? Add structural equivalence check. */
+
+ /* ??? This should eventually just return false. */
+ return lang_hooks.types_compatible_p (inner_type, outer_type);
+ }
return false;
}
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