[PATCH][RFC] Do not stream all zeros for gcda files.

[Nathan Sidwell]

On 6/17/20 2:44 AM, Martin Liška wrote:
> Hello.
> 
> As mentioned in the PR, gcda files tend to occupy a large disk space
> when each running process streams to its own directory. The test-case
> in the PR has very low coverage and so that the data file contain
> a lot of zero records.
> 
> The patch is attempt to not stream these zero COUNTERS:
> 
> a-tramp3d-v4.gcda:    01a10000:  38:COUNTERS arcs 19 counts (all zero)
> a-tramp3d-v4.gcda:                   0: 0 0 0 0 0 0 0 0
> a-tramp3d-v4.gcda:                   8: 0 0 0 0 0 0 0 0
> a-tramp3d-v4.gcda:                  16: 0 0 0
> 
> Here we stream -19 as count and any of the 0 is streamed.

neat

> 
> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
> The patch survives PGO bootstrap of GCC and it shrinks size of gcda
> file from 17MB to 12MB.
> 
> One alternative approach could be to use a normal compression (zlib, zstd)
> for output file? That can save even more space.

What's the size of zlib (or other) compression of that 17MB file?

nathan

-- 
Nathan Sidwell