[SPARC] Errata workaround for GRLIB-TN-0010

[SPARC] Errata workaround for GRLIB-TN-0010

This patch provides a workaround for the errata described in GRLIB-TN-0010.

If the workaround is enabled it will:

 * Insert a NOP between load instruction and atomic
   instruction (swap, ldstub, casa).

 * Insert a NOP at branch target if load in delay slot
   and atomic instruction at branch target.

It is applicable to UT700.

2017-11-29  Daniel Cederman  <cederman@gaisler.com>

gcc/
	* config/sparc/sparc.c (atomic_insn_p): New function.
	(sparc_do_work_around_errata): Insert NOP instructions to
	prevent sequences that could trigger the TN-0010 errata for
	UT700.
	* config/sparc/sync.md (atomic_compare_and_swap_leon3_1): Make
	instruction referable in atomic_insns_p.

From-SVN: r255236