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Re: [PATCH] gcov: Mark BBs that do not correspond to a line in source code (PR gcov-profile/79891).
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.
> 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)