Re: [RFC, rs6000, v2] Fix alignment of non-Altivec vector struct fields

[Richard Biener <richard dot guenther at gmail dot com>]

On Mon, Jul 14, 2014 at 8:55 PM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
> Hello,
>
> this is an attempt to update the prior patch:
> https://gcc.gnu.org/ml/gcc-patches/2014-07/msg00635.html
> to add a -Wpsabi note as discussed.
>
> However, this is causing a bit of difficulties.  First of all, the warning
> triggers in a larger number of tests -- which was probably to be expected
> since a number of tests in the suite explicitly work on GCC vectors defined
> using various vector_size values, and any size except 16 will result in the
> warning.  Note that the warning gets issued at the site of definition of
> the structure type -- it does not have to be used in a function call.
>
> More problematic is that this new warning causes four tests to fail
> (it's actually 38 new FAILS since each of the tests fails in multiple
> optimization levels):
>
> FAIL: gcc.c-torture/execute/20050316-1.c compilation
> gcc.c-torture/execute/20050316-1.c:53:9: note: the layout of aggregates containing vectors with 8-byte alignment has changed in GCC 4.10
> FAIL: gcc.c-torture/execute/20050316-3.c compilation
> gcc.c-torture/execute/20050316-3.c:26:9: note: the layout of aggregates containing vectors with 8-byte alignment has changed in GCC 4.10
> FAIL: gcc.c-torture/execute/20050604-1.c compilation
> gcc.c-torture/execute/20050604-1.c:12:1: note: the layout of aggregates containing vectors with 8-byte alignment has changed in GCC 4.10
> FAIL: gcc.c-torture/execute/pr23135.c compilation
> gcc.c-torture/execute/pr23135.c:20:1: note: the layout of aggregates containing vectors with 8-byte alignment has changed in GCC 4.10
>
> Unfortunately, while most of the tests in the suite use the dg-test
> framework which ignores "note" messages, the gcc.c-torture/execute
> tests still use the old "torture" test framework, which does *not*.
> (Also, in the old framework you cannot even add dg-... commands to
> ignore those messages for a certain test, or add a -Wno-psabi option.)
>
> Therefore, I'm not proposing to commit this patch as-is, but would
> like to ask for feedback on how to best proceed with this.
>
> One option might be to  move the affected tests to the dg-test framework.
> Or else we might decide we don't actually need a warning for this change,
> since it only affects GCC synthetic vectors, where we might not have made
> strict ABI guarantees anyway ...
>
> Thoughts?

> cat gcc/testsuite/gcc.c-torture/execute/pr38151.x
set additional_flags "-Wno-psabi"
return 0


> Bye,
> Ulrich
>
>
> gcc/ChangeLog:
>
>         * config/rs6000/rs6000-protos.h (rs6000_special_adjust_field_align_p):
>         Add prototype.
>         * config/rs6000/rs6000.c (rs6000_special_adjust_field_align_p): New
>         function.
>         * config/rs6000/sysv4.h (ADJUST_FIELD_ALIGN): Call it.
>         * config/rs6000/linux64.h (ADJUST_FIELD_ALIGN): Likewise.
>         * config/rs6000/freebsd64.h (ADJUST_FIELD_ALIGN): Likewise.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.target/powerpc/ppc64-abi-warn-3.c: New test.
>
>
>
> Index: gcc/config/rs6000/rs6000-protos.h
> ===================================================================
> --- gcc/config/rs6000/rs6000-protos.h   (revision 212147)
> +++ gcc/config/rs6000/rs6000-protos.h   (working copy)
> @@ -155,6 +155,7 @@
>
>  #ifdef TREE_CODE
>  extern unsigned int rs6000_data_alignment (tree, unsigned int, enum data_align);
> +extern bool rs6000_special_adjust_field_align_p (tree, unsigned int);
>  extern unsigned int rs6000_special_round_type_align (tree, unsigned int,
>                                                      unsigned int);
>  extern unsigned int darwin_rs6000_special_round_type_align (tree, unsigned int,
> Index: gcc/config/rs6000/rs6000.c
> ===================================================================
> --- gcc/config/rs6000/rs6000.c  (revision 212147)
> +++ gcc/config/rs6000/rs6000.c  (working copy)
> @@ -5878,6 +5878,32 @@
>    return align;
>  }
>
> +/* Previous GCC releases forced all vector types to have 16-byte alignment.  */
> +
> +bool
> +rs6000_special_adjust_field_align_p (tree field, unsigned int computed)
> +{
> +  if (TARGET_ALTIVEC && TREE_CODE (TREE_TYPE (field)) == VECTOR_TYPE)
> +    {
> +      if (computed != 128)
> +       {
> +         static bool warned;
> +         if (!warned && warn_psabi)
> +           {
> +             warned = true;
> +             inform (input_location,
> +                     "the layout of aggregates containing vectors with"
> +                     " %d-byte alignment has changed in GCC 4.10",
> +                     computed / BITS_PER_UNIT);
> +           }
> +       }
> +      /* In current GCC there is no special case.  */
> +      return false;
> +    }
> +
> +  return false;
> +}
> +
>  /* AIX increases natural record alignment to doubleword if the first
>     field is an FP double while the FP fields remain word aligned.  */
>
> Index: gcc/config/rs6000/sysv4.h
> ===================================================================
> --- gcc/config/rs6000/sysv4.h   (revision 212147)
> +++ gcc/config/rs6000/sysv4.h   (working copy)
> @@ -292,7 +292,7 @@
>  /* An expression for the alignment of a structure field FIELD if the
>     alignment computed in the usual way is COMPUTED.  */
>  #define ADJUST_FIELD_ALIGN(FIELD, COMPUTED)                                  \
> -       ((TARGET_ALTIVEC && TREE_CODE (TREE_TYPE (FIELD)) == VECTOR_TYPE)     \
> +       (rs6000_special_adjust_field_align_p ((FIELD), (COMPUTED))            \
>          ? 128 : COMPUTED)
>
>  #undef  BIGGEST_FIELD_ALIGNMENT
> Index: gcc/config/rs6000/linux64.h
> ===================================================================
> --- gcc/config/rs6000/linux64.h (revision 212147)
> +++ gcc/config/rs6000/linux64.h (working copy)
> @@ -246,7 +246,7 @@
>  /* PowerPC64 Linux word-aligns FP doubles when -malign-power is given.  */
>  #undef  ADJUST_FIELD_ALIGN
>  #define ADJUST_FIELD_ALIGN(FIELD, COMPUTED) \
> -  ((TARGET_ALTIVEC && TREE_CODE (TREE_TYPE (FIELD)) == VECTOR_TYPE)    \
> +  (rs6000_special_adjust_field_align_p ((FIELD), (COMPUTED))           \
>     ? 128                                                               \
>     : (TARGET_64BIT                                                     \
>        && TARGET_ALIGN_NATURAL == 0                                     \
> Index: gcc/config/rs6000/freebsd64.h
> ===================================================================
> --- gcc/config/rs6000/freebsd64.h       (revision 212147)
> +++ gcc/config/rs6000/freebsd64.h       (working copy)
> @@ -367,7 +367,7 @@
>  /* PowerPC64 Linux word-aligns FP doubles when -malign-power is given.  */
>  #undef  ADJUST_FIELD_ALIGN
>  #define ADJUST_FIELD_ALIGN(FIELD, COMPUTED) \
> -  ((TARGET_ALTIVEC && TREE_CODE (TREE_TYPE (FIELD)) == VECTOR_TYPE)     \
> +  (rs6000_special_adjust_field_align_p ((FIELD), (COMPUTED))           \
>     ? 128                                                                \
>     : (TARGET_64BIT                                                      \
>        && TARGET_ALIGN_NATURAL == 0                                      \
> Index: gcc/testsuite/gcc.target/powerpc/ppc64-abi-warn-3.c
> ===================================================================
> --- /dev/null
> +++ gcc/testsuite/gcc.target/powerpc/ppc64-abi-warn-3.c (revision 0)
> @@ -0,0 +1,9 @@
> +/* { dg-do compile { target { powerpc*-*-linux* && lp64 } } } */
> +/* { dg-require-effective-target powerpc_altivec_ok } */
> +/* { dg-options "-maltivec" } */
> +
> +struct test
> +  {
> +    int a __attribute__((vector_size (8)));
> +  }; /* { dg-message "note: the layout of aggregates containing vectors with 8-byte alignment has changed" } */
> +
> --
>   Dr. Ulrich Weigand
>   GNU/Linux compilers and toolchain
>   Ulrich.Weigand@de.ibm.com
>