analyzer: consider empty ranges and zero byte accesses [PR106845]

analyzer: consider empty ranges and zero byte accesses [PR106845]

This patch adds handling of empty ranges in bit_range and byte_range and
adds an assertion to member functions that assume a positive size.
Further, the patch fixes an ICE caused by an empty byte_range passed to
byte_range::exceeds_p.

Regression-tested on Linux x86_64.

2022-09-10  Tim Lange  <mail@tim-lange.me>

gcc/analyzer/ChangeLog:

	PR analyzer/106845
	* region-model.cc (region_model::check_region_bounds):
	Bail out if 0 bytes were accessed.
	* store.cc (byte_range::dump_to_pp):
	Add special case for empty ranges.
	(byte_range::exceeds_p): Restrict to non-empty ranges.
	(byte_range::falls_short_of_p): Restrict to non-empty ranges.
	* store.h (bit_range::empty_p): New function.
	(bit_range::get_last_byte_offset): Restrict to non-empty ranges.
	(byte_range::empty_p): New function.
	(byte_range::get_last_byte_offset): Restrict to non-empty ranges.

gcc/testsuite/ChangeLog:

	PR analyzer/106845
	* gcc.dg/analyzer/out-of-bounds-zero.c: New test.
	* gcc.dg/analyzer/pr106845.c: New test.