On Fri, Feb 17, 2012 at 9:51 PM, Thomas Schwinge
<tho...@codesourcery.com> wrote:
> Hi!
>
> How do we move this issue forward?
>
> On Mon, 23 Jan 2012 15:46:34 +0100, Bernd Schmidt <ber...@codesourcery.com>
> wrote:
>> On 11/29/2011 05:35 PM, Mitchell, Mark wrote:
>> >>> So, I still think this patch is the best way to go forward, and it
>> >> does
>> >>> fix incorrect code generation. Would appreciate an OK.
>> >>
>> >> Ping.
>> >
>> > If you don't hear any objections within a week, please proceed.
>>
>> That was committed a while ago. The part in stor-layout.c that stops us
>> from promoting bitfields to normal fields apparently caused some
>> testsuite regressions in sh tests, where some optimization dump scans
>> show that we can't perform the optimizations if there are BIT_FIELD_REFs
>> rather than a normal member access.
>>
>> The testcases use things like
>> enum something field:8;
>> and I think applying strict-volatile-bitfields to enums is probably
>> meaningless. Should we adjust semantics so that the compiler is free to
>> optimize enum bitfields? The patch would look something like the below.
>> Thomas has tested this on arm and sh with our internal tree.
>>
>>
>> Bernd
>>
>>
>> Index: gcc/stor-layout.c
>> ===================================================================
>> --- gcc/stor-layout.c (revision 355696)
>> +++ gcc/stor-layout.c (working copy)
>> @@ -665,8 +665,7 @@
>> may make a volatile object later. */
>> if (TYPE_SIZE (type) != 0
>> && TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST
>> - && GET_MODE_CLASS (TYPE_MODE (type)) == MODE_INT
>> - && flag_strict_volatile_bitfields <= 0)
>> + && GET_MODE_CLASS (TYPE_MODE (type)) == MODE_INT)
>> {
>> enum machine_mode xmode
>> = mode_for_size_tree (DECL_SIZE (decl), MODE_INT, 1);
>> @@ -674,7 +673,12 @@
>>
>> if (xmode != BLKmode
>> && !(xalign > BITS_PER_UNIT && DECL_PACKED (decl))
>> - && (known_align == 0 || known_align >= xalign))
>> + && (known_align == 0 || known_align >= xalign)
>> + && (flag_strict_volatile_bitfields <= 0
>> + /* Same size makes strict volatile bitfields
>> meaningless. */
>> + || GET_MODE_SIZE (xmode) == GET_MODE_SIZE
>> (TYPE_MODE (type))
>> + /* Strict volatile bitfields shouldn't apply to
>> enums. */
>> + || TREE_CODE (type) == ENUMERAL_TYPE))
What about BOOLEAN_TYPE bitfields? Thus, why not explicitely
spell out && TREE_CODE (type) == INTEGER_TYPE?
>> {
>> DECL_ALIGN (decl) = MAX (xalign, DECL_ALIGN (decl));
>> DECL_MODE (decl) = xmode;
>>
>
>
> Grüße,
> Thomas
