[PATCH] Add offset_int to guard HOST_WIDE_INT overflow (PR tree-optimization/82042).

[Martin Liška]

On 09/20/2017 05:47 PM, Richard Biener wrote:
> On Wed, Sep 20, 2017 at 9:50 AM, Martin Liška <mliska@suse.cz> wrote:
>> Hi.
>>
>> This is partial fix for the PR, where I calculate 2 offsets in offset_int type.
>>
>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
>>
>> Ready to be installed?
> 
> That seems to poorly handle the cases in offset_overlap_p.  What kind of
> overflow do we see here?

We hit:

        (const:DI (plus:DI (symbol_ref:DI ("a") [flags 0x40] <var_decl 0x7ffff7fe6ea0 a>)
                (const_int -9223372036854775805 [0x8000000000000003])))) "/home/marxin/Programming/testcases/pr82042.c":8 81 {*movdi_internal}

and:

        (const:DI (plus:DI (symbol_ref:DI ("a") [flags 0x40] <var_decl 0x7ffff7fe6ea0 a>)
                (const_int 9223372036854775806 [0x7ffffffffffffffe])))) 81 {*movdi_internal}

The UBSAN error is:
../../gcc/tree-ssa-alias.c:704:30: runtime error: signed integer overflow: 9223372036854775806 * 8 cannot be represented in type 'long int'

Martin

> 
> Richard.
> 
>> Martin
>>
>> gcc/ChangeLog:
>>
>> 2017-09-20  Martin Liska  <mliska@suse.cz>
>>
>>         PR tree-optimization/82042
>>         * alias.c (memrefs_conflict_p): Calculate offset in offset_int
>>         type.
>>         * cse.c (use_related_value): Likewise.
>> ---
>>  gcc/alias.c | 10 ++++++++--
>>  gcc/cse.c   | 14 ++++++++++----
>>  2 files changed, 18 insertions(+), 6 deletions(-)
>>
>>