analyzer: improvements to logging/dumping

analyzer: improvements to logging/dumping

This patch adds various information to -fdump-analyzer and
-fdump-analyzer-stderr to make it easier to track down
problems with state explosions in the exploded_graph.

It logs the number of unprocessed nodes in the worklist, for
the case where the upper limit on exploded nodes is reached.

It prints:
[a] a bar chart showing the number of exploded nodes by function, and

[b] bar charts for each function showing the number of exploded nodes
    per supernode/BB, and

[c] bar charts for each function showing the number of excess exploded
    nodes per supernode/BB beyond the limit
    (--param=analyzer-max-enodes-per-program-point), where that limit
    was reached

I've found these helpful in finding exactly where we fail to consolidate
state, leading to state explosions and false negatives due to the
thresholds being reached.

The patch also adds a "superedge::dump" member function I found myself
needing.

gcc/ChangeLog:
	* Makefile.in (ANALYZER_OBJS): Add analyzer/bar-chart.o.

gcc/analyzer/ChangeLog:
	* bar-chart.cc: New file.
	* bar-chart.h: New file.
	* engine.cc: Include "analyzer/bar-chart.h".
	(stats::log): Only log the m_num_nodes kinds that are non-zero.
	(stats::dump): Likewise when dumping.
	(stats::get_total_enodes): New.
	(exploded_graph::get_or_create_node): Increment the per-point-data
	m_excess_enodes when hitting the per-program-point limit on
	enodes.
	(exploded_graph::print_bar_charts): New.
	(exploded_graph::log_stats): Log the number of unprocessed enodes
	in the worklist.  Call print_bar_charts.
	(exploded_graph::dump_stats): Print the number of unprocessed
	enodes in the worklist.
	* exploded-graph.h (stats::get_total_enodes): New decl.
	(struct per_program_point_data): Add field m_excess_enodes.
	(exploded_graph::print_bar_charts): New decl.
	* supergraph.cc (superedge::dump): New.
	(superedge::dump): New.
	* supergraph.h (supernode::get_function): New.
	(superedge::dump): New decl.
	(superedge::dump): New decl.