Re: [PATCH] Fix host_size_t_cst_p predicate

[Richard Sandiford <rdsandiford at googlemail dot com>]

Richard Biener <richard.guenther@gmail.com> writes:
> On Thu, Oct 27, 2016 at 5:06 PM, Martin Liška <mliska@suse.cz> wrote:
>> On 10/27/2016 03:35 PM, Richard Biener wrote:
>>> On Thu, Oct 27, 2016 at 9:41 AM, Martin Liška <mliska@suse.cz> wrote:
>>>> Running simple test-case w/o the proper header file causes ICE:
>>>> strncmp ("a", "b", -1);
>>>>
>>>> 0xe74462 tree_to_uhwi(tree_node const*)
>>>>         ../../gcc/tree.c:7324
>>>> 0x90a23f host_size_t_cst_p
>>>>         ../../gcc/fold-const-call.c:63
>>>> 0x90a23f fold_const_call(combined_fn, tree_node*, tree_node*,
>>>> tree_node*, tree_node*)
>>>>         ../../gcc/fold-const-call.c:1512
>>>> 0x787b01 fold_builtin_3
>>>>         ../../gcc/builtins.c:8385
>>>> 0x787b01 fold_builtin_n(unsigned int, tree_node*, tree_node**, int, bool)
>>>>         ../../gcc/builtins.c:8465
>>>> 0x9052b1 fold(tree_node*)
>>>>         ../../gcc/fold-const.c:11919
>>>> 0x6de2bb c_fully_fold_internal
>>>>         ../../gcc/c/c-fold.c:185
>>>> 0x6e1f6b c_fully_fold(tree_node*, bool, bool*)
>>>>         ../../gcc/c/c-fold.c:90
>>>> 0x67cbbf c_process_expr_stmt(unsigned int, tree_node*)
>>>>         ../../gcc/c/c-typeck.c:10369
>>>> 0x67cfbd c_finish_expr_stmt(unsigned int, tree_node*)
>>>>         ../../gcc/c/c-typeck.c:10414
>>>> 0x6cb578 c_parser_statement_after_labels
>>>>         ../../gcc/c/c-parser.c:5430
>>>> 0x6cd333 c_parser_compound_statement_nostart
>>>>         ../../gcc/c/c-parser.c:4944
>>>> 0x6cdbde c_parser_compound_statement
>>>>         ../../gcc/c/c-parser.c:4777
>>>> 0x6c93ac c_parser_declaration_or_fndef
>>>>         ../../gcc/c/c-parser.c:2176
>>>> 0x6d51ab c_parser_external_declaration
>>>>         ../../gcc/c/c-parser.c:1574
>>>> 0x6d5c09 c_parser_translation_unit
>>>>         ../../gcc/c/c-parser.c:1454
>>>> 0x6d5c09 c_parse_file()
>>>>         ../../gcc/c/c-parser.c:18173
>>>> 0x72ffd2 c_common_parse_file()
>>>>         ../../gcc/c-family/c-opts.c:1087
>>>>
>>>> Following patch improves the host_size_t_cst_p predicate.
>>>>
>>>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
>>>>
>>>> Ready to be installed?
>>>
>>> I believe the wi::min_precision (t, UNSIGNED) <= sizeof (size_t) *
>>> CHAR_BIT test is now redundant.
>>>
>>> OTOH it was probably desired to allow -1 here?  A little looking back
>>> in time should tell.
>>
>> Ok, it started with r229922, where it was changed from:
>>
>>   if (tree_fits_uhwi_p (len) && p1 && p2)
>>     {
>>       const int i = strncmp (p1, p2, tree_to_uhwi (len));
>> ...
>>
>> to current version:
>>
>>     case CFN_BUILT_IN_STRNCMP:
>>       {
>>         bool const_size_p = host_size_t_cst_p (arg2, &s2);
>>
>> Thus I'm suggesting to change to back to it.
>>
>> Ready to be installed?
>
> Let's ask Richard.

The idea with the:

  wi::min_precision (t, UNSIGNED) <= sizeof (size_t) * CHAR_BIT

test was to stop us attempting 64-bit size_t operations on ILP32 hosts.
I think we still want that.

Thanks,
Richard