[SPARC] Errata workaround for GRLIB-TN-0012

[SPARC] Errata workaround for GRLIB-TN-0012

This patch provides a workaround for the errata described in GRLIB-TN-0012.

If the workaround is enabled it will:

 * Prevent any floating-point operation from being placed in the
   delay slot of an annulled integer branch.

 * Place a NOP at the branch target of an integer branch if it is
   a floating-point operation or a floating-point branch.

It is applicable to GR712RC.

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

gcc/
	* config/sparc/sparc.c (fpop_insn_p): New function.
	(sparc_do_work_around_errata): Insert NOP instructions to
	prevent sequences that could trigger the TN-0012 errata for
	GR712RC.
	(pass_work_around_errata::gate): Also test sparc_fix_gr712rc.
	* config/sparc/sparc.md (fix_gr712rc): New attribute.
	(in_branch_annul_delay): Prevent floating-point instructions
	in delay slot of annulled integer branch.

From-SVN: r255234