On 30 March 2012 20:29, Kenneth Zadeck <zad...@naturalbridge.com> wrote:
> ramana
>
> i get the same failure on the trunk without my patch.
>
In which case I apologise and will file a bug report separately. I
should really have checked :( .
Ramana
>
> kenny
>
> On 03/30/2012 07:36 AM, Ramana Radhakrishnan wrote:
>>
>> Hi
>>
>>
>>> I have tested this on an x86_64 with both the force lowering on and off
>>> and
>>> neither cause any regressions as well as extensive testing on my port.
>>>
>> So, just out of curiosity, I decided to run this through a
>> cross-build and noticed the following ICE with eglibc. I haven't had
>> the time to debug this further but it does appear as though it could
>> do with some more testing on some more ports and this probably needs
>> some tuning as you say.
>>
>> $>
>> /work/cross-build/fsf/arm-none-linux-gnueabi/tools-lowersubregchanges-patched/bin/arm-none-linux-gnueabi-gcc
>> -c -O2 ./besttry.c -mfloat-abi=soft -march=armv5te
>> ./besttry.c: In function ‘_IO_new_file_write’:
>> ./besttry.c:36:1: internal compiler error: in get_loop_body, at
>> cfgloop.c:831
>>
>> $> cat besttry.c
>> __extension__ typedef int __ssize_t;
>> extern __thread int __libc_errno __attribute__ ((tls_model
>> ("initial-exec")));
>> struct _IO_FILE {
>> int _fileno;
>> int _flags2;
>> };
>> typedef struct _IO_FILE _IO_FILE;
>> _IO_new_file_write (f,
>> data,
>> n)
>> _IO_FILE *f;
>> {
>> __ssize_t to_do = n;
>> while (to_do> 0)
>> {
>> __ssize_t count =
>> (__builtin_expect (f->_flags2& 2, 0) ?
>>
>> ({ unsigned int _sys_result = ({ register int _a1 asm ("r0"), _nr asm
>> ("r7");
>> int _a3tmp = (int) ((to_do));
>> int _a2tmp = (int) ((data));
>> register int _a2 asm ("a2") = _a2tmp;
>> register int _a3 asm ("a3") = _a3tmp; _nr = ((0 + 4));
>> asm volatile ("swi 0x0 @ syscall " "SYS_ify(write)" : "=r"
>> (_a1) : "r" (_nr) , "r" (_a1), "r" (_a2), "r" (_a3) : "memory"); _a1;
>> });
>> if (__builtin_expect (((unsigned int) (_sys_result)>= 0xfffff001u),
>> 0))
>> { (__libc_errno = ((-(_sys_result))));
>> _sys_result = (unsigned int) -1; }
>> (int) _sys_result; })
>> : __write (f->_fileno, data, to_do));
>> if (count< 0)
>> {
>> break;
>> }
>> to_do -= count;
>> }
>> }
>>
>>
>> Ramana
>>
>> On 29 March 2012 22:10, Kenneth Zadeck<zad...@naturalbridge.com> wrote:
>>>
>>> This patch takes a different approach to fixing PR52543 than does the
>>> patch
>>> in
>>>
>>> http://gcc.gnu.org/ml/gcc-patches/2012-03/msg00641.html
>>>
>>> This patch transforms the lower-subreg pass(es) from unconditionally
>>> splitting wide moves, zero extensions, and shifts, so that it now takes
>>> into
>>> account the target specific costs and only does the transformations if it
>>> is
>>> profitable.
>>>
>>> Unconditional splitting is a problem that not only occurs on the AVR but
>>> is
>>> also a problem on the ARM NEON and my private port. Furthermore, it is a
>>> problem that is likely to occur on most modern larger machines since
>>> these
>>> machines are more likely to have fast instructions for moving things that
>>> are larger than word mode.
>>>
>>> At compiler initialization time, each mode that is larger that a word
>>> mode
>>> is examined to determine if the cost of moving a value of that mode is
>>> less
>>> expensive that inserting the proper number of word sided moves. If it
>>> is
>>> cheaper to split it up, a bit is set to allow moves of that mode to be
>>> lowered.
>>>
>>> A similar analysis is made for the zero extensions and shifts except that
>>> lower subreg had been (and is still limited to only breaking up these
>>> operations if the target size was twice the size of word mode.) Also, if
>>> the analysis determines that there are no profitable transformations, the
>>> pass exits quickly without doing any analysis.
>>>
>>> It is quite likely that most ports will have to be adjusted after this
>>> patch
>>> is accepted. For instance, the analysis discovers that there are no
>>> profitable transformations to be performed on the x86-64. Since this
>>> is
>>> not my platform, I have no idea if these are the correct settings. But
>>> the
>>> pass uses the standard insn_rtx_cost interface and it is the port
>>> maintainers responsibility to not lie to the optimization passes so this
>>> extra work in stage one should be acceptable.
>>>
>>> I do know from a private conversation with Richard Sandiford, that mips
>>> patches are likely forthcoming.
>>>
>>> There is preprocessor controlled code that prints out the cost analysis.
>>> Only a summary of this can go in the subregs dump file because the
>>> analysis
>>> is called from backend_init_target and so the dump file is not available.
>>> But it is very useful to define LOG_COSTS when adjusting your port.
>>>
>>> There is also preprocessor code that forces all of the lowering
>>> operations
>>> to marked as profitable. This is useful in debugging the new logic.
>>>
>>> Both of these preprocessor symbols are documented at the top of the pass.
>>>
>>> I have tested this on an x86_64 with both the force lowering on and off
>>> and
>>> neither cause any regressions as well as extensive testing on my port.
>>>
>>> Ok to commit?
>>>
>>> Kenny
>>>
>>> 2012-03-29 Kenneth Zadeck<zad...@naturalbridge.com>
>>>
>>> * toplev.c (backend_init_target): Call initializer for lower-subreg
>>> pass.
>>>
>>> * lower-subreg.c (move_modes_to_split, splitting_ashift,
>>> splitting_lshiftrt)
>>> splitting_zext, splitting_some_shifts, twice_word_mode,
>>> something_to_do,
>>> word_mode_move_cost, move_zero_cost): New static vars.
>>> (compute_move_cost, profitable_shift_p, init_lower_subreg): New
>>> functions.
>>> (find_pseudo_copy, resolve_simple_move): Added code to only split
>>> based
>>> on costs.
>>> (find_decomposable_subregs): Added code to mark as decomposable
>>> moves that are not profitable.
>>> (find_decomposable_shift_zext): Added code to only decompose
>>> shifts and zext if profitable.
>>> (resolve_shift_zext): Added comment.
>>> (decompose_multiword_subregs): Dump list of profitable
>>> transformations. Add code to skip non profitable transformations.
>>>
>>> *rtl.h(init_lower_subreg): Added declaration.
>>>
>>>
>
