[Ada] Compile-time evaluation of predicate checks

[Ada] Compile-time evaluation of predicate checks

This patch recognizes case of dynamic predicates on integer subtypes
that are simple enough to be evaluated statically when the argument is
itself a literal. Even though in many cases such predicate checks will
be removed by the back-end with any level of optimization, it is
preferable to perform this constant folding in the front-end, wich also
cleans up the output of CCG, as well as producing explicit warnings when
the test will fail.

2019-07-11  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_ch6.adb (Can_Fold_Predicate_Call): New function,
	subsidiary of Expand_Call_Helper, to compute statically a
	predicate check when the argument is a static integer.

gcc/testsuite/

	* gnat.dg/predicate11.adb: New testcase.

From-SVN: r273386