[C/C++ PATCH] Reorganize c-common.c's convert_and_check
Manuel López-Ibáñez
lopezibanez@gmail.com
Mon Nov 13 00:43:00 GMT 2006
Roger,
Argh! I was going to do something similar with the Wcoercion project
patches. Unfortunately for me, your changes breaks this patch that was
waiting for approval:
http://gcc.gnu.org/ml/gcc-patches/2006-11/msg00248.html
So, what is the policy in this situation? Should I modify, retest and
resubmit this patch ? Also, I am going to heavily modify
convert_and_check in the following patches. Do you want me to CC you
in that case?
Cheers,
Manuel.
On 12/11/06, Roger Sayle <roger@eyesopen.com> wrote:
>
> This is one of the major installments in the on-going TREE_OVERFLOW
> clean-ups. Currently, when asked to truncate an INTEGER_CST to a
> narrower type, the middle-end may set the TREE_OVERFLOW flag on the
> result. Even though the semantics of signed and unsigned truncation
> are well-defined in the middle-end, the setting TREE_OVERFLOW has
> historically been a source of problems in tree-ssa optimizers, as
> it disables many transformations and triggers less well tested code
> paths.
>
> The propsed goal is to change fold_convert_const_int_from_int so
> that it no longer sets TREE_OVERFLOW or TREE_CONSTANT_OVERFLOW.
>
> The major remaining user of this functionality is the convert_and_check
> function in the C family front-ends, that uses the TREE_OVERFLOW from
> these truncations to issue front-end diagnostics. It turns out that
> its relatively simple to use the middle-end function int_fits_type
> which is intended for exactly this use. This reduces the overflow
> bit pollution of trees in the tree-ssa optimizers.
>
>
> The following patch has been tested (in conjunction with my recently
> posted C++ clean-up) on x86_64-unknown-linux-gnu, with a full "make
> bootstrap", all default languages, and regression tested with a
> top-level "make -k check" with no new failures. Critically, no
> changes in the C/C++ diagnostics issued anywhere in the testsuite.
>
> I believe that the rationalization of this logic in a single
> front-end function, makes it easier to see what's going on, and
> for front-end maintainers to tune as they wish.
>
> Ok for mainline? I'd appreciate it if anyone with access to Plum-Hall
> or similar validation suite could give it a spin. Hopefully, folks
> agree this untangling of front-ends from the middle-end is a direction
> that we want to go.
>
>
>
> 2006-11-12 Roger Sayle <roger@eyesopen.com>
>
> * c-common.c (constant_fits_type_p): Delete.
> (unsigned_conversion_warning): Delete. Integrate into...
> (convert_and_check): Reorganize and simplify to avoid dependence
> upon the middle-end setting TREE_OVERFLOW on integral conversions,
> by using int_fits_type directly.
>
>
> Index: c-common.c
> ===================================================================
> *** c-common.c (revision 118625)
> --- c-common.c (working copy)
> *************** const struct fname_var_t fname_vars[] =
> *** 499,505 ****
> {NULL, 0, 0},
> };
>
> - static int constant_fits_type_p (tree, tree);
> static tree check_case_value (tree);
> static bool check_case_bounds (tree, tree, tree *, tree *);
>
> --- 499,504 ----
> *************** overflow_warning (tree value)
> *** 957,988 ****
> }
> }
>
> - /* Print a warning if a large constant is truncated to unsigned,
> - or if -Wconversion is used and a constant < 0 is converted to unsigned.
> - Invoke this function on every expression that might be implicitly
> - converted to an unsigned type. */
> -
> - static void
> - unsigned_conversion_warning (tree result, tree operand)
> - {
> - tree type = TREE_TYPE (result);
> -
> - if (TREE_CODE (operand) == INTEGER_CST
> - && TREE_CODE (type) == INTEGER_TYPE
> - && TYPE_UNSIGNED (type)
> - && skip_evaluation == 0
> - && !int_fits_type_p (operand, type))
> - {
> - if (!int_fits_type_p (operand, c_common_signed_type (type)))
> - /* This detects cases like converting -129 or 256 to unsigned char. */
> - warning (OPT_Woverflow,
> - "large integer implicitly truncated to unsigned type");
> - else
> - warning (OPT_Wconversion,
> - "negative integer implicitly converted to unsigned type");
> - }
> - }
> -
> /* Print a warning about casts that might indicate violation
> of strict aliasing rules if -Wstrict-aliasing is used and
> strict aliasing mode is in effect. OTYPE is the original
> --- 956,961 ----
> *************** check_main_parameter_types (tree decl)
> *** 1100,1118 ****
> }
>
>
> - /* Nonzero if constant C has a value that is permissible
> - for type TYPE (an INTEGER_TYPE). */
> -
> - static int
> - constant_fits_type_p (tree c, tree type)
> - {
> - if (TREE_CODE (c) == INTEGER_CST)
> - return int_fits_type_p (c, type);
> -
> - c = convert (type, c);
> - return !TREE_OVERFLOW (c);
> - }
> -
> /* Nonzero if vector types T1 and T2 can be converted to each other
> without an explicit cast. */
> int
> --- 1073,1078 ----
> *************** vector_types_convertible_p (tree t1, tre
> *** 1134,1169 ****
> tree
> convert_and_check (tree type, tree expr)
> {
> ! tree t = convert (type, expr);
> ! if (TREE_CODE (t) == INTEGER_CST)
> ! {
> ! if (TREE_OVERFLOW (t))
> ! {
> ! TREE_OVERFLOW (t) = 0;
>
> ! /* Do not diagnose overflow in a constant expression merely
> ! because a conversion overflowed. */
> ! TREE_CONSTANT_OVERFLOW (t) = CONSTANT_CLASS_P (expr)
> ! && TREE_CONSTANT_OVERFLOW (expr);
>
> ! /* No warning for converting 0x80000000 to int. */
> ! if (!(TYPE_UNSIGNED (type) < TYPE_UNSIGNED (TREE_TYPE (expr))
> ! && TREE_CODE (TREE_TYPE (expr)) == INTEGER_TYPE
> ! && TYPE_PRECISION (type) == TYPE_PRECISION (TREE_TYPE (expr))))
> ! /* If EXPR fits in the unsigned version of TYPE,
> ! don't warn unless pedantic. */
> ! if ((pedantic
> ! || TYPE_UNSIGNED (type)
> ! || !constant_fits_type_p (expr,
> ! c_common_unsigned_type (type)))
> ! && skip_evaluation == 0)
> ! warning (OPT_Woverflow,
> ! "overflow in implicit constant conversion");
> }
> else
> ! unsigned_conversion_warning (t, expr);
> }
> ! return t;
> }
>
> /* A node in a list that describes references to variables (EXPR), which are
> --- 1094,1150 ----
> tree
> convert_and_check (tree type, tree expr)
> {
> ! tree result;
>
> ! if (TREE_TYPE (expr) == type)
> ! return expr;
>
> ! result = convert (type, expr);
> ! if (TREE_CODE (result) != INTEGER_CST
> ! || skip_evaluation)
> ! return result;
> !
> ! if (TREE_CODE (expr) == INTEGER_CST
> ! && (TREE_CODE (type) == INTEGER_TYPE
> ! || TREE_CODE (type) == ENUMERAL_TYPE)
> ! && !int_fits_type_p (expr, type))
> ! {
> ! /* Do not diagnose overflow in a constant expression merely
> ! because a conversion overflowed. */
> ! if (TREE_OVERFLOW (result))
> ! {
> ! TREE_CONSTANT_OVERFLOW (result) = TREE_CONSTANT_OVERFLOW (expr);
> ! TREE_OVERFLOW (result) = TREE_OVERFLOW (expr);
> ! }
> !
> ! if (TYPE_UNSIGNED (type))
> ! {
> ! /* This detects cases like converting -129 or 256 to
> ! unsigned char. */
> ! if (!int_fits_type_p (expr, c_common_signed_type (type)))
> ! warning (OPT_Woverflow,
> ! "large integer implicitly truncated to unsigned type");
> ! else
> ! warning (OPT_Wconversion,
> ! "negative integer implicitly converted to unsigned type");
> }
> else
> ! {
> ! if (!int_fits_type_p (expr, c_common_unsigned_type (type)))
> ! warning (OPT_Woverflow,
> ! "overflow in implicit constant conversion");
> ! /* No warning for converting 0x80000000 to int. */
> ! else if (pedantic
> ! && (TREE_CODE (TREE_TYPE (expr)) != INTEGER_TYPE
> ! || TYPE_PRECISION (TREE_TYPE (expr))
> ! != TYPE_PRECISION (type)))
> ! warning (OPT_Woverflow,
> ! "overflow in implicit constant conversion");
> ! }
> }
> ! else if (TREE_OVERFLOW (result))
> ! warning (OPT_Woverflow, "overflow in implicit constant conversion");
> ! return result;
> }
>
> /* A node in a list that describes references to variables (EXPR), which are
>
>
> Roger
> --
>
>
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