Re: Values of WIDE_INT_MAX_ELTS in gcc11 and gcc12 are different

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Nov 05, 2021 at 04:11:36PM +0000, Qing Zhao wrote:
> 3076       if (TREE_CODE (TREE_TYPE (lhs)) != BOOLEAN_TYPE
> 3077           && tree_fits_uhwi_p (var_size)
> 3078           && (init_type == AUTO_INIT_PATTERN
> 3079               || !is_gimple_reg_type (var_type))
> 3080           && int_mode_for_size (tree_to_uhwi (var_size) * BITS_PER_UNIT,
> 3081                                 0).exists ())
> 3082         {
> 3083           unsigned HOST_WIDE_INT total_bytes = tree_to_uhwi (var_size);
> 3084           unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
> 3085           memset (buf, (init_type == AUTO_INIT_PATTERN
> 3086                         ? INIT_PATTERN_VALUE : 0), total_bytes);
> 3087           tree itype = build_nonstandard_integer_type
> 3088                          (total_bytes * BITS_PER_UNIT, 1);
> 
> The exact failing point is at function “set_min_and_max_values_for_integral_type”:
> 
> 2851   gcc_assert (precision <= WIDE_INT_MAX_PRECISION);
> 
> For _Complex long double,  “precision” is 256.  
> In GCC11, “WIDE_INT_MAX_PRECISION” is 192,  in GCC12, it’s 512. 
> As a result, the above assertion failed on GCC11. 
> 
> I am wondering what’s the best fix for this issue in gcc11? 

Even for gcc 12 the above is wrong, you can't blindly assume that
build_nonstandard_integer_type will work for arbitrary precisions,
and even if it works that it will actually work.
The fact that such a mode exist is one thing, but
targetm.scalar_mode_supported_p should be tested for whether the mode
is actually supported.

	Jakub