Re: [PATCH] Fix bitmap_bit_in_range_p (PR tree-optimization/82493).

[Jeff Law <law@redhat.com>]

On 10/16/2017 06:03 AM, Martin Liška wrote:
> On 10/13/2017 04:59 PM, Jeff Law wrote:
>> On 10/13/2017 07:02 AM, Martin Liška wrote:
>>> On 10/12/2017 11:54 PM, Jeff Law wrote:
>>>> On 10/11/2017 12:13 AM, Martin Liška wrote:
>>>>> 2017-10-10  Martin Liska  <mliska@suse.cz>
>>>>>
>>>>> 	PR tree-optimization/82493
>>>>> 	* sbitmap.c (bitmap_bit_in_range_p): Fix the implementation.
>>>>> 	(test_range_functions): New function.
>>>>> 	(sbitmap_c_tests): Likewise.
>>>>> 	* selftest-run-tests.c (selftest::run_tests): Run new tests.
>>>>> 	* selftest.h (sbitmap_c_tests): New function.
>>>> I went ahead and committed this along with a patch to fix the off-by-one
>>>> error in live_bytes_read.  Bootstrapped and regression tested on x86.
>>>>
>>>> Actual patch attached for archival purposes.
>>>>
>>>> Jeff
>>>>
>>>
>>> Hello.
>>>
>>> I wrote a patch that adds various gcc_checking_asserts and I hit following:
>>>
>>> ./xgcc -B. /home/marxin/Programming/gcc/gcc/testsuite/gfortran.dg/char_result_12.f90 -c -O2
>>> during GIMPLE pass: dse
>>> /home/marxin/Programming/gcc/gcc/testsuite/gfortran.dg/char_result_12.f90:7:0:
>>>
>>>   program testat
>>>  
>>> internal compiler error: in bitmap_check_index, at sbitmap.h:105
>>> 0x1c014c1 bitmap_check_index
>>> 	../../gcc/sbitmap.h:105
>>> 0x1c01fa7 bitmap_bit_in_range_p(simple_bitmap_def const*, unsigned int, unsigned int)
>>> 	../../gcc/sbitmap.c:335
>>> 0x1179002 live_bytes_read
>>> 	../../gcc/tree-ssa-dse.c:497
>>> 0x117935a dse_classify_store
>>> 	../../gcc/tree-ssa-dse.c:595
>>> 0x1179947 dse_dom_walker::dse_optimize_stmt(gimple_stmt_iterator*)
>>> 	../../gcc/tree-ssa-dse.c:786
>>> 0x1179b6e dse_dom_walker::before_dom_children(basic_block_def*)
>>> 	../../gcc/tree-ssa-dse.c:853
>>> 0x1a6f659 dom_walker::walk(basic_block_def*)
>>> 	../../gcc/domwalk.c:308
>>> 0x1179cb9 execute
>>> 	../../gcc/tree-ssa-dse.c:907
>>>
>>> Where we call:
>>> Breakpoint 1, bitmap_bit_in_range_p (bmap=0x29d6cd0, start=0, end=515) at ../../gcc/sbitmap.c:335
>>> 335	  bitmap_check_index (bmap, end);
>>> (gdb) p *bmap
>>> $1 = {n_bits = 256, size = 4, elms = {255}}
>>>
>>> Is it a valid call or should caller check indices?
>> It doesn't look valid to me.  I'll dig into it.
>>
>> In general the sbitmap interface requires callers to DTRT -- failure can
>> easily lead to an out of bounds read or write.  It's one of the things I
>> really dislike about the sbitmap implementation.
>>
>> So it's safe to assume that I'm fully supportive of adding more testing
>> to catch this kind thing.
>>
>> Jeff
>>
> 
> Good.
> 
> Should I prepare fix for the ICE I mentioned or have you been working on that?
I've already got a patch for it.  I'll likely commit it this morning.

jeff