Re: [Patch, RTL] Eliminate redundant vec_select moves.

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Tue, Dec 10, 2013 at 2:33 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Dec 10, 2013 at 2:25 PM, Tejas Belagod <belagod.tejas@gmail.com> wrote:
>> On 10 December 2013 21:51, H.J. Lu <hjl.tools@gmail.com> wrote:
>>> On Tue, Dec 10, 2013 at 1:09 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>> On Tue, Dec 10, 2013 at 12:39 PM, Richard Henderson <rth@redhat.com> wrote:
>>>>> On 12/10/2013 10:44 AM, Richard Sandiford wrote:
>>>>>> Sorry, I don't understand.  I never said it was invalid.  I said
>>>>>> (subreg:SF (reg:V4SF X) 1) was invalid if (reg:V4SF X) represents
>>>>>> a single register.  On a little-endian target, the offset cannot be
>>>>>> anything other than 0 in that case.
>>>>>>
>>>>>> So the CANNOT_CHANGE_MODE_CLASS code above seems to be checking for
>>>>>> something that is always invalid, regardless of the target.  That kind
>>>>>> of situation should be rejected by target-independent code instead.
>>>>>
>>>>> But, we want to disable the subreg before we know whether or not (reg:V4SF X)
>>>>> will be allocated to a single hard register.  That is something that we can't
>>>>> know in target-independent code before register allocation.
>>>>
>>>> I tried Kirill's patch.  But LRA isn't prepared to handle it:
>>>>
>>>> spawn -ignore SIGHUP /export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
>>>> -B/export/build/gnu/gcc/build-x86_64-linux/gcc/
>>>> /export/gnu/import/git/gcc/gcc/testsuite/gcc.dg/atomic/c11-atomic-exec-1.c
>>>> -B/export/build/gnu/gcc/build-x86_64-linux/x86_64-unknown-linux-gnu/32/libatomic/
>>>> -L/export/build/gnu/gcc/build-x86_64-linux/x86_64-unknown-linux-gnu/32/libatomic/.libs
>>>> -latomic -fno-diagnostics-show-caret -fdiagnostics-color=never -O1
>>>> -std=c11 -pedantic-errors -lm -m32 -o ./c11-atomic-exec-1.exe^M
>>>> /export/gnu/import/git/gcc/gcc/testsuite/gcc.dg/atomic/c11-atomic-exec-1.c:
>>>> In function 'test_simple_assign':^M
>>>> /export/gnu/import/git/gcc/gcc/testsuite/gcc.dg/atomic/c11-atomic-exec-1.c:81:1:
>>>> internal compiler error: Maximum number of LRA constraint passes is
>>>> achieved (30)^M
>>>> ^M
>>>> 0x88ed77 lra_constraints(bool)^M
>>>>         /export/gnu/import/git/gcc/gcc/lra-constraints.c:3871^M
>>>> 0x87fe8c lra(_IO_FILE*)^M
>>>>         /export/gnu/import/git/gcc/gcc/lra.c:2331^M
>>>> 0x840f76 do_reload^M
>>>>         /export/gnu/import/git/gcc/gcc/ira.c:5455^M
>>>> 0x840f76 rest_of_handle_reload^M
>>>>         /export/gnu/import/git/gcc/gcc/ira.c:5584^M
>>>> 0x840f76 execute^M
>>>>         /export/gnu/import/git/gcc/gcc/ira.c:5613^M
>>>>
>>>
>>> I got several hundred failures like this in GCC
>>> testsuite with -m32 and -m64 on Linux/x86-64.
>>>
>>
>> I think this is the same as:
>>
>> http://gcc.gnu.org/ml/gcc/2013-12/msg00086.html
>>
>> LRA does not seem to know how to resolve subregs with non-zero offsets
>> that don't map to a full-hardreg.
>>
>
> Looks like it.  I am rebuilding and retesting Kirill's patch +
> Vladimir's patch.
>

Vladimir's patch cuts down the ICEs to 53. I still got

spawn -ignore SIGHUP /export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/
/export/gnu/import/git/gcc/gcc/testsuite/gcc.dg/vect/slp-2.c
-fno-diagnostics-show-caret -fdiagnostics-color=never -msse2
-ftree-vectorize -fno-vect-cost-model -fno-common -O2
-fdump-tree-vect-details -lm -o ./slp-2.exe^M
/export/gnu/import/git/gcc/gcc/testsuite/gcc.dg/vect/slp-2.c: In
function 'main1':^M
/export/gnu/import/git/gcc/gcc/testsuite/gcc.dg/vect/slp-2.c:131:1:
internal compiler error: Max. number of generated reload insns per
insn is achieved (90)^M
^M
0x88ecb3 lra_constraints(bool)^M
        /export/gnu/import/git/gcc/gcc/lra-constraints.c:3986^M
0x87fe8c lra(_IO_FILE*)^M
        /export/gnu/import/git/gcc/gcc/lra.c:2331^M
0x840f76 do_reload^M
        /export/gnu/import/git/gcc/gcc/ira.c:5455^M
0x840f76 rest_of_handle_reload^M
        /export/gnu/import/git/gcc/gcc/ira.c:5584^M
0x840f76 execute^M
        /export/gnu/import/git/gcc/gcc/ira.c:5613^M
Please submit a full bug report,^M
with preprocessed source if appropriate.^M
Please include the complete backtrace with any bug report.^M
See <http://gcc.gnu.org/bugs.html> for instructions.^M
compiler exited with status 1

I also got the wrong code regression:

FAIL: gfortran.dg/round_4.f90  -O0  execution test
FAIL: gfortran.dg/round_4.f90  -O1  execution test
FAIL: gfortran.dg/round_4.f90  -O2  execution test
FAIL: gfortran.dg/round_4.f90  -O3 -fomit-frame-pointer  execution test
FAIL: gfortran.dg/round_4.f90  -O3 -fomit-frame-pointer
-funroll-all-loops -finline-functions  execution test
FAIL: gfortran.dg/round_4.f90  -O3 -fomit-frame-pointer -funroll-loops
 execution test
FAIL: gfortran.dg/round_4.f90  -O3 -g  execution test
FAIL: gfortran.dg/round_4.f90  -Os  execution test

My hjl/subreg branch doesn't have those regressions.

-- 
H.J.