Richard Sandiford wrote:
> Janis Johnson <[EMAIL PROTECTED]> writes:
>
>> On Mon, 2007-09-17 at 23:41 +0200, Andreas Schwab wrote:
>>
>>> Janis Johnson <[EMAIL PROTECTED]> writes:
>>>
>>>
>>>> Bootstrap of powerpc64-linux fails building libgfortran with:
>>>>
>>>> /home/janis/gcc_trunk_anonsvn/gcc/libgfortran/io/read.c: In function
>>>> 'set_integer':
>>>> /home/janis/gcc_trunk_anonsvn/gcc/libgfortran/io/read.c:81: internal
>>>> compiler error: in set_variable_part, at var-tracking.c:2381
>>>> Please submit a full bug report, with preprocessed source if appropriate.
>>>> See <http://gcc.gnu.org/bugs.html> for instructions.
>>>>
>>>> My last successful build was revision 128522; earliest known break
>>>> was 128536, still breaks with 128551.
>>>>
>>> Bisection has identified this change:
>>>
>>> 2007-09-16 Richard Sandiford <[EMAIL PROTECTED]>
>>>
>>> * dse.c (find_shift_sequence): Allow word as well as subword shifts.
>>> Do the tentative shift expansion with the DF_NO_INSN_RESCAN flag set.
>>> Fix the call to insn_rtx_cost. Skip access sizes that require a
>>> real truncation of the store register. Use convert_move instead
>>> of gen_lowpart when narrowing the result.
>>> (replace_read): Use convert_move instead of gen_lowpart when
>>> narrowing the store rhs.
>>>
>> My hunt just found the same patch Here's a small test that fails
>> with cc1 for powerpc64-linux with "-O2 -g -m64 -mstrict-align":
>> -------------
>> extern void *memcpy (void *, const void *, signed long);
>>
>> void
>> set_integer (void *dest, __int128_t value, int length)
>> {
>> switch (length)
>> {
>> case 16:
>> {
>> __int128_t tmp = value;
>> memcpy (dest, (void *) &tmp, length);
>> }
>> break;
>> case 1:
>> {
>> signed char tmp = value;
>> memcpy (dest, (void *) &tmp, length);
>> }
>> break;
>> }
>> }
>> -----------
>> Janis
>>
>
> I think this is a latent bug in var-tracking.c. It's getting confused
> by the negative offsets in:
>
> (insn:HI 17 47 19 4 /tmp/foo.c:11 (set (reg:DI 26 26 [orig:124 tmp+-7 ] [124])
> (lshiftrt:DI (reg:DI 31 31 [orig:141 value ] [141])
> (const_int 56 [0x38]))) 292 {*lshrdi3_internal1} (nil))
>
> (insn:HI 19 17 21 4 /tmp/foo.c:11 (set (reg:DI 27 27 [orig:125 tmp+-6 ] [125])
> (lshiftrt:DI (reg:DI 31 31 [orig:141 value ] [141])
> (const_int 48 [0x30]))) 292 {*lshrdi3_internal1} (nil))
>
> where the registers have come from paradoxical subregs of QImode registers.
> (DSE itself didn't create those; combine did. DSE just created DImode
> shift instructions.)
>
> FWIW, the part of the patch that exposed the bug as the change from
> "access_bytes < UNITS_PER_WORD" to "access_bytes <= UNITS_PER_WORD".
> Your testcase passes if we change that back.
>
>
i would prefer that the above change be reverted and the rest of the
patch left in.
kenny
> From my POV of view, feel free to commit that change until the underlying
> var-tracking bug is fixed. Alternatively, I think it'd be OK to revert
> the whole of my patch _and_ revert Kenny's patch. (Please don't just
> revert mine, as it would reintroduce a bootstrap failure on MIPS targets.)
>
> I'm afraid I won't have time to work on this myself. Hopefully Kenny
> will. (At the end of the day, I was only trying to fix MIPS breakage
> in the original DSE patch, rather than asking Kenny to it for me. ;))
>
> Richard
>
