Re: Values of WIDE_INT_MAX_ELTS in gcc11 and gcc12 are different

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Nov 9, 2021 at 6:48 PM Qing Zhao <qing.zhao@oracle.com> wrote:
>
> So, based on the discussion so far,  is the following patch good to go?

OK.

Thanks,
Richard.

> Let me know if you have more comments on the following patch:
>
> (At the same time, I am testing this patch on both x86 and aarch64)
>
> thanks.
>
> Qing
>
> diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
> index 0cba95411a6..e8fd16b9c21 100644
> --- a/gcc/internal-fn.c
> +++ b/gcc/internal-fn.c
> @@ -3059,10 +3059,10 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
>        mark_addressable (lhs);
>        tree var_addr = build_fold_addr_expr (lhs);
>
> -      tree value = (init_type == AUTO_INIT_PATTERN) ?
> -                   build_int_cst (integer_type_node,
> -                                  INIT_PATTERN_VALUE) :
> -                   integer_zero_node;
> +      tree value = (init_type == AUTO_INIT_PATTERN)
> +                   ? build_int_cst (integer_type_node,
> +                                    INIT_PATTERN_VALUE)
> +                   : integer_zero_node;
>        tree m_call = build_call_expr (builtin_decl_implicit (BUILT_IN_MEMSET),
>                                      3, var_addr, value, var_size);
>        /* Expand this memset call.  */
> @@ -3073,15 +3073,17 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
>        /* If this variable is in a register use expand_assignment.
>          For boolean scalars force zero-init.  */
>        tree init;
> +      scalar_int_mode var_mode;
>        if (TREE_CODE (TREE_TYPE (lhs)) != BOOLEAN_TYPE
>           && tree_fits_uhwi_p (var_size)
>           && (init_type == AUTO_INIT_PATTERN
>               || !is_gimple_reg_type (var_type))
>           && int_mode_for_size (tree_to_uhwi (var_size) * BITS_PER_UNIT,
> -                               0).exists ())
> +                               0).exists (&var_mode)
> +         && have_insn_for (SET, var_mode))
>         {
>           unsigned HOST_WIDE_INT total_bytes = tree_to_uhwi (var_size);
> -         unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
> +         unsigned char *buf = XALLOCAVEC (unsigned char, total_bytes);
>           memset (buf, (init_type == AUTO_INIT_PATTERN
>                         ? INIT_PATTERN_VALUE : 0), total_bytes);
>           tree itype = build_nonstandard_integer_type
> diff --git a/gcc/testsuite/gcc.target/i386/auto-init-6.c b/gcc/testsuite/gcc.target/i386/auto-init-6.c
> index 339f8bc2966..e53385f0eb7 100644
> --- a/gcc/testsuite/gcc.target/i386/auto-init-6.c
> +++ b/gcc/testsuite/gcc.target/i386/auto-init-6.c
> @@ -1,4 +1,6 @@
>  /* Verify pattern initialization for complex type automatic variables.  */
> +/* Note, _Complex long double is initialized to zeroes due to the current
> +   implemenation limitation.  */
>  /* { dg-do compile } */
>  /* { dg-options "-ftrivial-auto-var-init=pattern -march=x86-64 -mtune=generic -msse" } */
>
> @@ -15,6 +17,6 @@ _Complex long double foo()
>    return result;
>  }
>
> -/* { dg-final { scan-assembler-times "long\t-16843010" 10  { target { ! ia32 } } } } */
> -/* { dg-final { scan-assembler-times "long\t-16843010" 6  { target { ia32 } } } } */
> +/* { dg-final { scan-assembler-times "long\t0" 8  { target { ! ia32 } } } } */
> +/* { dg-final { scan-assembler-times "long\t-16843010" 6  } } */
>
>
>
>
> > On Nov 9, 2021, at 4:44 AM, Richard Biener <richard.guenther@gmail.com> wrote:
> >
> > On Tue, Nov 9, 2021 at 10:10 AM Jakub Jelinek <jakub@redhat.com> wrote:
> >>
> >> On Tue, Nov 09, 2021 at 08:13:57AM +0100, Richard Biener wrote:
> >>>> Hi, I tried both the following patches:
> >>>>
> >>>> Patch1:
> >>>>
> >>>> [opc@qinzhao-ol8u3-x86 gcc]$ git diff
> >>>> diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
> >>>> index 0cba95411a6..ca49d2b4514 100644
> >>>> --- a/gcc/internal-fn.c
> >>>> +++ b/gcc/internal-fn.c
> >>>> @@ -3073,12 +3073,14 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
> >>>>       /* If this variable is in a register use expand_assignment.
> >>>>         For boolean scalars force zero-init.  */
> >>>>       tree init;
> >>>> +      scalar_int_mode var_mode;
> >>>>       if (TREE_CODE (TREE_TYPE (lhs)) != BOOLEAN_TYPE
> >>>>          && tree_fits_uhwi_p (var_size)
> >>>>          && (init_type == AUTO_INIT_PATTERN
> >>>>              || !is_gimple_reg_type (var_type))
> >>>>          && int_mode_for_size (tree_to_uhwi (var_size) * BITS_PER_UNIT,
> >>>> -                               0).exists ())
> >>>> +                               0).exists (&var_mode)
> >>>> +         && targetm.scalar_mode_supported_p (var_mode))
> >>>>        {
> >>>>          unsigned HOST_WIDE_INT total_bytes = tree_to_uhwi (var_size);
> >>>>          unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
> >>>>
> >>>> AND
> >>>>
> >>>> Patch2:
> >>>> diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
> >>>> index 0cba95411a6..7f129655926 100644
> >>>> --- a/gcc/internal-fn.c
> >>>> +++ b/gcc/internal-fn.c
> >>>> @@ -3073,12 +3073,14 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
> >>>>       /* If this variable is in a register use expand_assignment.
> >>>>         For boolean scalars force zero-init.  */
> >>>>       tree init;
> >>>> +      scalar_int_mode var_mode;
> >>>>       if (TREE_CODE (TREE_TYPE (lhs)) != BOOLEAN_TYPE
> >>>>          && tree_fits_uhwi_p (var_size)
> >>>>          && (init_type == AUTO_INIT_PATTERN
> >>>>              || !is_gimple_reg_type (var_type))
> >>>>          && int_mode_for_size (tree_to_uhwi (var_size) * BITS_PER_UNIT,
> >>>> -                               0).exists ())
> >>>> +                               0).exists (&var_mode)
> >>>> +         && have_insn_for (SET, var_mode))
> >>>>        {
> >>>>          unsigned HOST_WIDE_INT total_bytes = tree_to_uhwi (var_size);
> >>>>          unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
> >>>>
> >>>> Have the same effect:
> >>>>
> >>>> 1. Resolved the ICE in gcc11;
> >>>> 2. For _Complex long double variables, both return FALSE, as a result, for PATTERN initialization of _Complex long double variables, now they are initialization with ZEROs instead of FEs.
> >>>>
> >>>> Let me know you opinion on this, If the above 2 is okay, then I might pick the above Patch 1 for the final patch to this issue.
> >>>
> >>> I think zero-initialization is OK, but I'd choose Patch2 for
> >>> consistency with what we do in the memcpy
> >>> folding.
> >>
> >> Note, I think the code leaks memory (buf is never freed) and
> >> should be allocated using
> >>  unsigned char *buf = XNEWVEC (unsigned char *, total_bytes);
> >> and deallocated with XDELETEVEC (buf);
> >
> > Oops.  I think the intention was to use XALLOCAVEC
> >
> >> If lhs is SSA_NAME, I think it would be easiest to use
> >> native_interpret_expr directly instead of finding some integral
> >> mode, after memset just native_interpret_expr.
> >
> > I've removed the native_interpret_expr path, I think it would be best to not
> > rely on expand_assignment for the case of a register destination.  The
> > intent is to do an integer move into the destination and avoid issues with
> > things like XFmode or other modes with padding (and possibly trapping loads).
> > So it should become some
> >
> > (set (subreg:IntMode ...) (const_wide_int ...))
> >
> > but my RTL fu is too weak to try and so we ended up with expand_assignment
> > which doesn't like V_C_E on SSA names on the LHS (well, because that's
> > not valid GIMPLE...).
> >
> >> Should be guarded by
> >> BITS_PER_UNIT == 8 && CHAR_BIT == 8 && BYTES_BIG_ENDIAN == WORDS_BIG_ENDIAN
> >> but I think the current code assumes at least that BITS_PER_UNIT == CHAR_BIT
> >> too anyway.
> >> That way you get directly a constant init instead of hopping through
> >> some integral mode which might not exist at all.
> >> If lhs is not SSA_NAME but var_type has COMPLEX_TYPE or VECTOR_TYPE, there
> >> is always an option to find var_mode only for the element type (i.e.
> >> TREE_TYPE (var_type), use var_size for the element size too, and after
> >> you compute init fold_build2 (COMPLEX_EXPR, ) or build_vector_from_val.
> >> For VECTOR_TYPE one would need to check if the vector mode is supported,
> >> sure (but if it isn't, it will go the BUILT_IN_MEMSET way, I'm pretty sure).
> >>
> >> Also,
> >>      tree value = (init_type == AUTO_INIT_PATTERN) ?
> >>                    build_int_cst (integer_type_node,
> >>                                   INIT_PATTERN_VALUE) :
> >>                    integer_zero_node;
> >> a few lines before has bad formatting, both ? and : should be at the start
> >> of next lines rather than on end of the previous ones.
> >>
> >>        Jakub
>