Re: [PATCH] Fix host_size_t_cst_p predicate

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

On Mon, Oct 31, 2016 at 3:56 PM, Martin Liška <mliska@suse.cz> wrote:
> On 10/31/2016 12:11 PM, Richard Biener wrote:
>> On Mon, Oct 31, 2016 at 11:18 AM, Richard Sandiford
>> <richard.sandiford@arm.com> wrote:
>>> Richard Biener <richard.guenther@gmail.com> writes:
>>>> On Mon, Oct 31, 2016 at 10:58 AM, Richard Sandiford
>>>> <richard.sandiford@arm.com> wrote:
>>>>> Richard Biener <richard.guenther@gmail.com> writes:
>>>>>> On Mon, Oct 31, 2016 at 10:10 AM, Martin Liška <mliska@suse.cz> wrote:
>>>>>>> On 10/31/2016 01:12 AM, Richard Sandiford wrote:
>>>>>>>> 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.
>>>>>>>
>>>>>>> OK, so is the consensus to add tree_fits_uhwi_p predicate to the current
>>>>>>> wi::min_precision check, right?
>>>>>>
>>>>>> Not sure.  If we have host_size_t_cst_p then we should have a corresponding
>>>>>> size_t host_size_t (const_tree) and should use those in pairs.  Not sure
>>>>>> why we have sth satisfying host_size_t_cst_p but not tree_fits_uhwi_p.
>>>>>
>>>>> It's the other way around: something can satisfy tree_fits_uhwi_p
>>>>> (i.e. fit within a uint64_t) but not fit within the host's size_t.
>>>>> The kind of case I'm thinking of is:
>>>>>
>>>>>   strncmp ("fi", "fo", (1L << 32) + 1)
>>>>>
>>>>> for an ILP32 host and LP64 target.  There's a danger that by passing
>>>>> the uint64_t value (1L << 32) + 1 to the host's strncmp that we'd
>>>>> truncate it to 1, giving the wrong result.
>>>>
>>>> Yes, but if it passes host_size_t_cst_p why does tree_to_uhwi ICE then?
>>>> (unless we have a > 64bit host size_t).
>>>
>>> Because in Martin's test case the length has a signed type.
>>> tree_to_uhwi then treats the argument as -1 to infinite precision
>>> rather than ~(size_t) 0 to infinite precision.
>>
>> Indeed.  So the bug is kind-of in the caller then.  OTOH we could simply
>> re-interpret the input as target size_t before doing the range check /
>> conversion.
>>
>> I believe fold_const_call has the general issue of not verifying argument types
>> before recognizing things as BUILT_IN_* (or the FE is at fault - but that's an
>> old discussion...)
>>
>> Richard.
>
> Updated and tested version of the patch that add types_compatible_p check
> to host_size_t_cst_p.
>
> Ready to be installed?

Ok.

Richard.

> Martin
>
>>
>>> Thanks,
>>> Richard
>