graphite: Tune parameters for OpenACC use

graphite: Tune parameters for OpenACC use

The default values of some parameters that restrict Graphite's
resource usage are too low for many OpenACC codes.  Furthermore,
exceeding the limits does not alwas lead to user-visible diagnostic
messages.

This commit increases the parameter values on OpenACC functions.  The
values were chosen to allow for the analysis of all "kernels" regions
in the SPEC ACCEL v1.3 benchmark suite.  Warnings about exceeded
Graphite-related limits are added to the -fopt-info-missed
output. Those warnings are phrased in a uniform way that intentionally
refers to the "data-dependence analysis" of "OpenACC loops" instead of
"a failure in Graphite" to make them easier to understand for users.

gcc/ChangeLog:

        * graphite-optimize-isl.c (optimize_isl): Adjust
	param_max_isl_operations value for OpenACC functions and add
	special warnings if value gets exceeded.

	* graphite-scop-detection.c (build_scops): Likewise for
	param_graphite_max_arrays_per_scop.

gcc/testsuite/ChangeLog:

        * gcc.dg/goacc/graphite-parameter-1.c: New test.
        * gcc.dg/goacc/graphite-parameter-2.c: New test.