Re: [PATCH] Fix compile-time hog in MPX boundary checking (PR target/84988).

["Martin Liška" <mliska@suse.cz>]

On 03/21/2018 10:36 AM, Richard Biener wrote:
> On Tue, Mar 20, 2018 at 10:44 PM, Richard Sandiford
> <richard.sandiford@linaro.org> wrote:
>> Jeff Law <law@redhat.com> writes:
>>> On 03/20/2018 01:36 PM, Martin Liška wrote:
>>>> Hi.
>>>>
>>>> This is a work-around to not iterate all members of array that can be huge.
>>>> As MPX will be removed in GCC 9.x, I hope it's acceptable. I don't want
>>>> to come
>>>> up with a new param for it.
>>>>
>>>> Survives tests&bootstrap on x86_64-linux-gnu.
>>>>
>>>> Martin
>>>>
>>>> gcc/ChangeLog:
>>>>
>>>> 2018-03-20  Martin Liska  <mliska@suse.cz>
>>>>
>>>>      PR target/84988
>>>>      * tree-chkp.c (CHKP_ARRAY_MAX_CHECK_STEPS): Define a new macro.
>>>>      (chkp_find_bound_slots_1): Limit number of iterations.
>>> Or just CLOSE/WONTFIX :-)
>>>
>>> I've got no objections here -- we want to  minimize the effort put into
>>> CHKP given its going to be deprecated.
>>
>> The problem is that this affects normal configs, not just ones with
>> MPX enabled.
> 
> Indeed.  It get's called via
> 
> #0  chkp_find_bound_slots_1 (type=0x7ffff69ee9d8, have_bound=0x2ed3868, offs=0)
>      at /space/rguenther/src/svn/early-lto-debug/gcc/tree-chkp.c:1708
> #1  0x0000000001379a13 in chkp_find_bound_slots (type=0x7ffff69ee9d8,
>      res=0x2ed3868)
>      at /space/rguenther/src/svn/early-lto-debug/gcc/tree-chkp.c:1754
> #2  0x0000000001377054 in chkp_type_bounds_count (type=0x7ffff69ee9d8)
>      at /space/rguenther/src/svn/early-lto-debug/gcc/tree-chkp.c:1009
> #3  0x00000000016c664f in ix86_function_arg_advance (cum_v=...,
>      mode=E_BLKmode, type=0x7ffff69ee9d8, named=true)
>      at /space/rguenther/src/svn/early-lto-debug/gcc/config/i386/i386.c:8621
> 8616        {
> 8617          /* Track if there are outgoing arguments on stack.  */
> 8618          if (cum->caller)
> 8619            cfun->machine->outgoing_args_on_stack = true;
> 8620
> 8621          cum->bnds_in_bt = chkp_type_bounds_count (type);
> 8622        }
> 8623    }
> 8624
> 8625    /* Define where to put the arguments to a function.
> 
> but I think we know POINTER_BOUNDS_TYPE_P etc. never return
> true if -fcheck-pointer-* or -mmpx is not enabled, right?  So we can
> guard the above call appropriately and save some compile-time
> for all of us?

Good observation, let me enhance the patch for the PR.

Martin

> 
> Richard.
> 
>> Thanks,
>> Richard