i get the same failure on the trunk without my patch.


On 03/30/2012 07:36 AM, Ramana Radhakrishnan wrote:

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.

-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,
      _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)
       to_do -= count;


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


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

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

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?


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_zext, splitting_some_shifts, twice_word_mode,
    word_mode_move_cost, move_zero_cost): New static vars.
    (compute_move_cost, profitable_shift_p, init_lower_subreg): New
    (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.

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