[Bug middle-end/51893] New: Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[Bug middle-end/51893] New: Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[aurelien.buhrig.gcc at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

             Bug #: 51893
           Summary: Wrong subword index computation in store_bit_field_1
                    on BIG_ENDIAN targets
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: aurelien.buhrig.gcc@gmail.com


Created attachment 26369
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26369
Patch

The subword index (wordnum) passed to operand_subword_force in
store_bit_field_1 is incorrect for BIG_ENDIAN targets when bitsize >
BITS_PER_WORD.

wordnum, which is used to get the subword of value, is
computed wrt the number of words needed by bitsize instead of the number of
words needed by the integer mode of the field, which is the mode used to
compute subwords.

For instance, for a 40bit field to be set by a DI reg (with HI words),
the offset of the LSWord of the DI reg should be 3, not 2 as currently
computed.

The attached patch seems to solve the issue. Tested on the C testsuite
without any regression (for my target only).

Note that this problem occurs on a "private" target (hardly reproducible).

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[aurelien.buhrig.gcc at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

Aurelien Buhrig <aurelien.buhrig.gcc at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |critical

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|critical                    |normal

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-01-18 23:06:20 UTC ---
I see the issue, one place does it right and the other does not.

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-01-19
                 CC|                            |ebotcazou at gcc dot
                   |                            |gnu.org
     Ever Confirmed|0                           |1

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-01-19 10:11:49 UTC ---
So, confirmed.

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |WAITING

--- Comment #3 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-01-19 10:47:45 UTC ---
Please try the fix for PR middle-end/50325.

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[aurelien.buhrig.gcc at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

--- Comment #4 from Aurelien Buhrig <aurelien.buhrig.gcc at gmail dot com> 2012-01-20 09:00:38 UTC ---
After modifying this patch for 4.6.1 this patch doesn't work (bitfld-3.c
testcase).

It doesn't affect the value subword offset computation (wordnum) when calling
operand_subword_force.

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

--- Comment #5 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-01-20 10:04:50 UTC ---
> After modifying this patch for 4.6.1 this patch doesn't work (bitfld-3.c
> testcase).

What do you mean exactly?  That gnat.dg/bitfld-3.c fails with the patch?

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[aurelien.buhrig.gcc at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

--- Comment #6 from Aurelien Buhrig <aurelien.buhrig.gcc at gmail dot com> 2012-01-20 10:32:22 UTC ---

(In reply to comment #5)
> > After modifying this patch for 4.6.1 this patch doesn't work (bitfld-3.c
> > testcase).
> 
> What do you mean exactly?  That gnat.dg/bitfld-3.c fails with the patch?

I mean the patch was likely done for 4.7, and I made very small adjustments to
enable patching on 4.6.1.

The testcase that fails is gcc.c-torture/execute/bitfld-3.c. Both with and
without (4.6.1 release) the patch. 
The patch I posted fixes the problem, but I don't know if it is general enough.

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

--- Comment #7 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-01-20 11:28:26 UTC ---
> The testcase that fails is gcc.c-torture/execute/bitfld-3.c. Both with and
> without (4.6.1 release) the patch. 
> The patch I posted fixes the problem, but I don't know if it is general enough.

OK, what are the values of the various parameters you have upon entering the
problematic block of code in store_bit_field_1?  Note that this code has been
working fine for years on 32-bit big-endian targets so this is unexpected.

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[aurelien.buhrig.gcc at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

--- Comment #8 from Aurelien Buhrig <aurelien.buhrig.gcc at gmail dot com> 2012-01-23 08:27:22 UTC ---
It seems the problem occurs with big endian targets when value is at least 4
times bigger than a word.
Example:
bitsize=40, value = reg:DI sub words-->HI. So wordnum = 3.

The for loop should start from LSWord to bitsize MSWord (wordnum).
So:
subword 3 from value, and calls  store_bit_fields_1 with bitsize <=
BITS_PER_WORD
then subword 2,
then subword 1
And subword 0 from value should be ignored.

Currently, the loop does not begins with subword 3, but with subword
"wordnum-1" which is 2. It is not the LSword of value, and the value stored in
the bitfield is (value << BITS_PER_WORD).

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[aurelien.buhrig.gcc at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

--- Comment #9 from Aurelien Buhrig <aurelien.buhrig.gcc at gmail dot com> 2012-03-20 16:22:52 UTC ---
Do you need additional information about this bug?
Any comment about the provided patch?

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW

--- Comment #10 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-03-20 22:03:27 UTC ---
> Do you need additional information about this bug?
> Any comment about the provided patch?

No, I think the patch is correct.  Please post it on gcc-patches@.

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

--- Comment #11 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-03-27 20:50:21 UTC ---
Author: ebotcazou
Date: Tue Mar 27 20:50:16 2012
New Revision: 185897

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=185897
Log:
    PR middle-end/51893
    * expmed.c (store_bit_field_1): Fix wordnum value for big-endian
    targets.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/expmed.c

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

--- Comment #12 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-03-28 09:06:30 UTC ---
Author: ebotcazou
Date: Wed Mar 28 09:06:03 2012
New Revision: 185909

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=185909
Log:
    PR middle-end/51893
    * expmed.c (store_bit_field_1): Fix wordnum value for big-endian
    targets.

Modified:
    branches/gcc-4_7-branch/gcc/ChangeLog
    branches/gcc-4_7-branch/gcc/expmed.c

[Bug middle-end/51893] Wrong subword index computation in store_bit_field_1 on BIG_ENDIAN targets

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51893

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.7.1

--- Comment #13 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-03-28 09:10:35 UTC ---
Fixed in the 4.7.x series.  Thanks for the bug report and the patch.