[amdgcn] Restrict registers available to non-kernel functions

[amdgcn] Restrict registers available to non-kernel functions

Restrict the number of SGPRs and VGPRs available to non-kernel functions
to improve compute-unit occupancy with multiple threads.

2019-11-15  Kwok Cheung Yeung  <kcy@codesourcery.com>

	gcc/
	* config/gcn/gcn.c (default_requested_args): New.
	(gcn_parse_amdgpu_hsa_kernel_attribute): Initialize requested args
	set with default_requested_args.
	(gcn_conditional_register_usage): Limit register usage of non-kernel
	functions.  Reassign fixed registers if a non-standard set of args is
	requested.
	* config/gcn/gcn.h (FIXED_REGISTERS): Fix registers according to ABI.

From-SVN: r278301