[PATCH] gcov: Mark BBs that do not correspond to a line in source code (PR gcov-profile/79891).
Richard Biener
rguenther@suse.de
Tue Mar 14 10:48:00 GMT 2017
On Tue, 14 Mar 2017, Martin Liška wrote:
> On 03/14/2017 11:30 AM, Richard Biener wrote:
> > On Tue, 14 Mar 2017, Martin Liška wrote:
> >
> >> On 03/14/2017 11:13 AM, Richard Biener wrote:
> >>> On Tue, 14 Mar 2017, Martin Liška wrote:
> >>>
> >>>> On 03/14/2017 10:12 AM, Richard Biener wrote:
> >>>>> On Tue, 14 Mar 2017, Martin Liška wrote:
> >>>>>
> >>>>>> On 03/14/2017 09:13 AM, Richard Biener wrote:
> >>>>>>> On Tue, 14 Mar 2017, Martin Liška wrote:
> >>>>>>>
> >>>>>>>> On 03/13/2017 04:16 PM, Richard Biener wrote:
> >>>>>>>>> On Mon, 13 Mar 2017, Martin Liška wrote:
> >>>>>>>>>
> >>>>>>>>>> On 03/13/2017 02:53 PM, Richard Biener wrote:
> >>>>>>>>>>> On Mon, 13 Mar 2017, Martin Liška wrote:
> >>>>>>>>>>>
> >>>>>>>>>>>> On 03/13/2017 02:01 PM, Richard Biener wrote:
> >>>>>>>>>>>>> On Mon, 13 Mar 2017, Richard Biener wrote:
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>> On Fri, 10 Mar 2017, Martin Liška wrote:
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> Hello.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> As briefly discussed in the PR, there are BB that do not correspond to a real
> >>>>>>>>>>>>>>> line in source
> >>>>>>>>>>>>>>> code. profile.c emits locations for all BBs that have a gimple statement
> >>>>>>>>>>>>>>> belonging to a line.
> >>>>>>>>>>>>>>> I hope these should be marked in gcov utility and not added in --all-block
> >>>>>>>>>>>>>>> mode to counts of lines.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> Patch survives make check RUNTESTFLAGS="gcov.exp".
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> Thanks for review and feedback.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> Humm, the patch doesn't seem to change the BBs associated with a line
> >>>>>>>>>>>>>> but rather somehow changes how we compute counts (the patch lacks a
> >>>>>>>>>>>>>> description of how you arrived at it). I expected the line-to-BB
> >>>>>>>>>>>>>> assignment process to be changed (whereever that is...).
> >>>>>>>>>>>>
> >>>>>>>>>>>> Currently, each basic block must belong to a source line. It's how gcov
> >>>>>>>>>>>> iterates all blocks (via lines).
> >>>>>>>>>>>>
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Ah, ok, looking at where output_location is called on I see we do not
> >>>>>>>>>>>>> assign any line to that block. But still why does
> >>>>>>>>>>>>> line->has_block (arc->src) return true?
> >>>>>>>>>>>>
> >>>>>>>>>>>> Good objection! Problematic that 4->5 edge really comes from the same line.
> >>>>>>>>>>>>
> >>>>>>>>>>>> <bb 4> [0.00%]:
> >>>>>>>>>>>> ret_7 = 111;
> >>>>>>>>>>>> PROF_edge_counter_10 = __gcov0.UuT[0];
> >>>>>>>>>>>> PROF_edge_counter_11 = PROF_edge_counter_10 + 1;
> >>>>>>>>>>>> __gcov0.UuT[0] = PROF_edge_counter_11;
> >>>>>>>>>>>>
> >>>>>>>>>>>> <bb 5> [0.00%]:
> >>>>>>>>>>>> # ret_1 = PHI <ret_5(3), ret_7(4)>
> >>>>>>>>>>>> goto <bb 7>; [0.00%]
> >>>>>>>>>>>
> >>>>>>>>>>> Yes, but that's basically meaningless, unless not all edges come from the
> >>>>>>>>>>> same line? I see nowhere where we'd explicitely assign lines to
> >>>>>>>>>>> edges so it must be gcov "reconstructing" this somewhere.
> >>>>>>>>>>
> >>>>>>>>>> That's why I added the another flag. We stream locations for basic blocks via
> >>>>>>>>>> 'output_location' function. And assignment blocks to lines happens here:
> >>>>>>>>>>
> >>>>>>>>>> static void
> >>>>>>>>>> add_line_counts (coverage_t *coverage, function_t *fn)
> >>>>>>>>>> {
> >>>>>>>>>> ...
> >>>>>>>>>> if (!ix || ix + 1 == fn->num_blocks)
> >>>>>>>>>> /* Entry or exit block */;
> >>>>>>>>>> else if (flag_all_blocks)
> >>>>>>>>>> {
> >>>>>>>>>> line_t *block_line = line;
> >>>>>>>>>>
> >>>>>>>>>> if (!block_line)
> >>>>>>>>>> block_line = &sources[fn->src].lines[fn->line];
> >>>>>>>>>>
> >>>>>>>>>> block->chain = block_line->u.blocks;
> >>>>>>>>>> block_line->u.blocks = block;
> >>>>>>>>>> }
> >>>>>>>>>>
> >>>>>>>>>> where line is always changes when we reach a BB that has a source line assigned. Thus it's changed
> >>>>>>>>>> for BB 4 and that's why BB 5 is added to same line.
> >>>>>>>>>
> >>>>>>>>> Ah, so this means we should "clear" the current line for BB 5 in
> >>>>>>>>> output_location? At least I don't see how your patch may not regress
> >>>>>>>>> some cases where the line wasn't output as an optimization?
> >>>>>>>>
> >>>>>>>> The new flag on block is kind of clearing that the BB is artificial and in fact does not
> >>>>>>>> belong to the line. I didn't want to do a bigger refactoring how blocks are iterated via lines.
> >>>>>>>>
> >>>>>>>> Can you be please more specific about such a case?
> >>>>>>>
> >>>>>>> in profile.c I see
> >>>>>>>
> >>>>>>> if (name_differs || line_differs)
> >>>>>>> {
> >>>>>>> if (!*offset)
> >>>>>>> {
> >>>>>>> *offset = gcov_write_tag (GCOV_TAG_LINES);
> >>>>>>> gcov_write_unsigned (bb->index);
> >>>>>>> name_differs = line_differs=true;
> >>>>>>> }
> >>>>>>>
> >>>>>>> ...
> >>>>>>>
> >>>>>>> so if line_differs is false we might not output GCOV_TAG_LINES either
> >>>>>>> because 1) optimization, less stuff output, 2) the block has no line.
> >>>>>>> Looks like we can't really distinguish those.
> >>>>>>
> >>>>>> Agree with that.
> >>>>>>
> >>>>>>>
> >>>>>>> Not sure how on the input side we end up associating a BB with
> >>>>>>> a line if nothing was output for it though.
> >>>>>>>
> >>>>>>> That is, with your change don't we need
> >>>>>>>
> >>>>>>> Index: gcc/profile.c
> >>>>>>> ===================================================================
> >>>>>>> --- gcc/profile.c (revision 246082)
> >>>>>>> +++ gcc/profile.c (working copy)
> >>>>>>> @@ -941,8 +941,6 @@ output_location (char const *file_name,
> >>>>>>> name_differs = !prev_file_name || filename_cmp (file_name,
> >>>>>>> prev_file_name);
> >>>>>>> line_differs = prev_line != line;
> >>>>>>>
> >>>>>>> - if (name_differs || line_differs)
> >>>>>>> - {
> >>>>>>> if (!*offset)
> >>>>>>> {
> >>>>>>> *offset = gcov_write_tag (GCOV_TAG_LINES);
> >>>>>>> @@ -950,6 +948,9 @@ output_location (char const *file_name,
> >>>>>>> name_differs = line_differs=true;
> >>>>>>> }
> >>>>>>>
> >>>>>>> + if (name_differs || line_differs)
> >>>>>>> + {
> >>>>>>> +
> >>>>>>> /* If this is a new source file, then output the
> >>>>>>> file's name to the .bb file. */
> >>>>>>> if (name_differs)
> >>>>>>>
> >>>>>>> to resolve this ambiguity? That is, _always_ emit GCOV_TAG_LINES
> >>>>>>> for a BB? So then a BB w/o GCOV_TAG_LINES does _not_ have any
> >>>>>>> lines associated.
> >>>>>>
> >>>>>> That should revolve it. Let me find and example where we do not emit
> >>>>>> GCOV_TAG_LINES jsut because there's not difference in lines.
> >>>>>
> >>>>> sth like
> >>>>>
> >>>>> a = b < 1 ? (c < 3 ? d : c);
> >>>>>
> >>>>> or even
> >>>>>
> >>>>> if (..) { ... } else { ... }
> >>>>
> >>>> These samples work, however your patch would break situations like:
> >>>>
> >>>> 1: 10:int main ()
> >>>> -: 11:{
> >>>> -: 12: int i;
> >>>> -: 13:
> >>>> 22: 14: for (i = 0; i < 10; i++) /* count(11) */
> >>>> 10: 15: noop (); /* count(10) */
> >>>>
> >>>> where 22 is summed as (1+10+11), which kind of makes sense as it contains
> >>>> of 3 statements.
> >>>
> >>> 22 is with my patch or without? I think 22 makes no sense.
> >>>
> >>> Richard.
> >>
> >> With your patch.
> >
> > I see. As said, I have zero (well, now some little ;)) knowledge
> > about gcov.
>
> :) I'll continue twiddling with that because even loop-less construct
> like:
>
> 1: 1:int foo(int b, int c, int d)
> -: 2:{
> 5: 3: int a = b < 1 ? (c < 3 ? d : c) : a;
> 2: 4: return a;
> -: 5:}
>
> gives bogus output with your patch (which I believe does proper thing).
Reading into the code (yes, it really seems it's for caching purposes
given we walk BBs in "random" order) I also observe
for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
gimple *stmt = gsi_stmt (gsi);
if (!RESERVED_LOCATION_P (gimple_location (stmt)))
output_location (gimple_filename (stmt), gimple_lineno
(stmt),
&offset, bb);
should use expand_location and then look at the spelling location,
otherwise we'll get interesting effects with macro expansion?
}
Richard.
> Martin
>
>
> >
> > Richard.
> >
> >> Martin
> >>
> >>>
> >>>> Martin
> >>>>
> >>>>>
> >>>>>
> >>>>>> Martin
> >>>>>>
> >>>>>>>
> >>>>>>> Richard.
> >>>>>>>
> >>>>>>>
> >>>>>>>> Hope Nathan will find time to provide review as he's familiar with content of gcov.c.
> >>>>>>>>
> >>>>>>>> Martin
> >>>>>>>>
> >>>>>>>>>
> >>>>>>>>> OTOH I don't know much about gcov format.
> >>>>>>>>>
> >>>>>>>>> Richard.
> >>>>>>>>>
> >>>>>>>>>> Martin
> >>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>> Richard.
> >>>>>>>>>>>
> >>>>>>>>>>>> Martin
> >>>>>>>>>>>>
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Richard.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>
> >>>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>>
> >>>>>
> >>>>
> >>>>
> >>>
> >>
> >>
> >
>
>
--
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)
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