Re: [PATCH] ipa-fnsummary: Remove inconsistent bp_pack_value

["Kewen.Lin" <linkw@linux.ibm.com>]

on 2021/9/21 下午2:16, Richard Biener wrote:
> On Tue, Sep 21, 2021 at 4:09 AM Kewen.Lin <linkw@linux.ibm.com> wrote:
>>
>> Hi Richi,
>>
>> Thanks for the review!
>>
>> on 2021/9/17 下午6:04, Richard Biener wrote:
>>> On Fri, Sep 17, 2021 at 12:03 PM Richard Biener
>>> <richard.guenther@gmail.com> wrote:
>>>>
>>>> On Fri, Sep 17, 2021 at 11:43 AM Kewen.Lin <linkw@linux.ibm.com> wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> When changing target_info with bitfield, I happened to find this
>>>>> inconsistent streaming in and out.  We have the streaming in:
>>>>>
>>>>>           bp_pack_value (&bp, info->inlinable, 1);
>>>>>           bp_pack_value (&bp, false, 1);
>>>>>           bp_pack_value (&bp, info->fp_expressions, 1);
>>>>>
>>>>> while the streaming out:
>>>>>
>>>>>           info->inlinable = bp_unpack_value (&bp, 1);
>>>>>           info->fp_expressions = bp_unpack_value (&bp, 1)
>>>>>
>>>>> The cleanup of Cilk Plus support seemed to miss to remove the bit
>>>>> streaming out but change with streaming false.
>>>>>
>>>>> By hacking fp_expression_p to return true always, I can see it
>>>>> reads the wrong fp_expressions value (false) out in wpa dumping.
>>>>>
>>>>> Bootstrapped and regress-tested on powerpc64le-linux-gnu Power9.
>>>>>
>>>>> Is it ok for trunk?
>>>>
>>>> OK for trunk and all affected branches (note we need to bump the
>>>> LTO minor version there).  The issue comes from the removal
>>>> of cilk+ in r8-4956 which removed the bp_unpack but replaced
>>>> the bp_pack ...
>>>>
>>>> It's a correctness issue as we'll read fp_expressions as always 'false'
>>>
>>> Btw, on branches we could also simply unpack a dummy bit to avoid
>>> changing the format.
>>>
>>
>> Committed in r12-3721.  Thanks!
>>
>> As suggested, the patch for branches is listed below.
>>
>> Is ok for branches 9, 10 and 11 after some trunk burn in time?
> 
> It's OK for branches without waiting, maybe you can do a LTO bootstrap
> on the branches for extra safety (just in case we're triggering some hidden
> issues due to the fix).

Thanks!  LTO bootstrapped on the branches, separately committed via
r11-9024, r10-10146 and r9-9740.

BR,
Kewen

> 
> Thanks,
> Richard.
> 
>> BR,
>> Kewen
>> -----
>> gcc/ChangeLog:
>>
>>         * ipa-fnsummary.c (inline_read_section): Unpack a dummy bit
>>         to keep consistent with the side of streaming out.
>>
>> ---
>> diff --git a/gcc/ipa-fnsummary.c b/gcc/ipa-fnsummary.c
>> index 18bbae145b9..bf635c1f78a 100644
>> --- a/gcc/ipa-fnsummary.c
>> +++ b/gcc/ipa-fnsummary.c
>> @@ -4403,13 +4403,20 @@ inline_read_section (struct lto_file_decl_data *file_data, const char *data,
>>        bp = streamer_read_bitpack (&ib);
>>        if (info)
>>         {
>> -          info->inlinable = bp_unpack_value (&bp, 1);
>> -          info->fp_expressions = bp_unpack_value (&bp, 1);
>> +         info->inlinable = bp_unpack_value (&bp, 1);
>> +         /* On the side of streaming out, there is still one bit
>> +            streamed out between inlinable and fp_expressions bits,
>> +            which was used for cilk+ before but now always false.
>> +            To remove the bit packing need to bump LTO minor version,
>> +            so unpack a dummy bit here to keep consistent instead.  */
>> +         bp_unpack_value (&bp, 1);
>> +         info->fp_expressions = bp_unpack_value (&bp, 1);
>>         }
>>        else
>>         {
>> -          bp_unpack_value (&bp, 1);
>> -          bp_unpack_value (&bp, 1);
>> +         bp_unpack_value (&bp, 1);
>> +         bp_unpack_value (&bp, 1);
>> +         bp_unpack_value (&bp, 1);
>>         }
>>
>>        count2 = streamer_read_uhwi (&ib);
>>