This patch gets the gimple FE to parse calls to internal functions.
The only non-obvious thing was how the functions should be written
to avoid clashes with real function names.  One option would be to
go the magic number of underscores route, but we already do that for
built-in functions, and it would be good to keep them visually
distinct.  In the end I borrowed the local/internal label convention
from asm and used:

  x = .SQRT (y);

2018-05-17  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* internal-fn.h (lookup_internal_fn): Declare
	* internal-fn.c (lookup_internal_fn): New function.
	* gimple.c (gimple_build_call_from_tree): Handle calls to
	internal functions.
	* gimple-pretty-print.c (dump_gimple_call): Print "." before
	internal function names.
	* tree-pretty-print.c (dump_generic_node): Likewise.
	* tree-ssa-scopedtables.c (expr_hash_elt::print): Likewise.

gcc/c/
	* gimple-parser.c: Include internal-fn.h.
	(c_parser_gimple_statement): Treat a leading CPP_DOT as a call.
	(c_parser_gimple_call_internal): New function.
	(c_parser_gimple_postfix_expression): Use it to handle CPP_DOT.
	Fix typos in comment.

gcc/testsuite/
	* gcc.dg/gimplefe-28.c: New test.
	* gcc.dg/asan/use-after-scope-9.c: Adjust expected output for
	internal function calls.
	* gcc.dg/goacc/loop-processing-1.c: Likewise.

From-SVN: r260316