Re: gcov questions

[Jim Wilson <jimw at sifive dot com>]

On 08/09/2018 02:38 AM, daro_ox@o2.pl wrote:
> Hello,   I wanted to ask what model for
> branch coverage does gcov use?

There is a comment at the start of gcc/profile.c that gives some details 
on how it works.  It is computing execution counts for edges in the 
control flow graph.  As for which edges get instrumented, basically, you 
construct a control flow graph, create a minimal spanning tree to cover 
the graph, and then you only need to instrument the edges not on the 
spanning tree, plus the function entry point.  You can compute the rest 
of the edge counts from that.  Then there are some tricks to improve 
efficiency by putting frequently executed edges on the minimal spanning 
tree, so that infrequently edges get instrumented.

Gcov was originally written in 1990, based on an idea that came from 
Knuth's Art of Computer Programming.  Ball & Larus wrote a nice paper in 
1994 that does a good job of covering the methods used, though they may 
not have been aware of gcov at the time as it hadn't been accepted into 
GCC yet.  This is "Optimally Profiling and Tracing Programs" TOPLAS July 
1994.  I don't know if there are free copies of that available.  There 
may be better references available now, as these techniques are pretty 
widely known nowadays

Jim