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

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

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?

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);