[PATCH] Fix host_size_t_cst_p predicate

[Richard Biener]

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.

> Thanks,
> Richard