[SPARC] Errata workaround for GRLIB-TN-0013

[SPARC] Errata workaround for GRLIB-TN-0013

This patch provides a workaround for the errata described in GRLIB-TN-0013.

If the workaround is enabled it will:

* Prevent div and sqrt instructions in the delay slot.

* Insert NOPs to prevent the sequence (div/sqrt) -> (two or three floating
  point operations or loads) -> (div/sqrt).

* Not insert NOPs if any of the floating point operations have a dependency
  on the destination register of the first (div/sqrt).

* Not insert NOPs if one of the floating point operations is a (div/sqrt).

* Insert NOPs to prevent (div/sqrt) followed by a branch.

It is applicable to GR712RC, UT700, and UT699.

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

gcc/
	* config/sparc/sparc.c (fpop_reg_depend_p): New function.
	(div_sqrt_insn_p): New function.
	(sparc_do_work_around_errata): Insert NOP instructions to
	prevent sequences that could trigger the TN-0013 errata for
	certain LEON3 processors.
	(pass_work_around_errata::gate): Also test sparc_fix_lost_divsqrt.
	(sparc_option_override): Set sparc_fix_lost_divsqrt appropriately.
	* config/sparc/sparc.md (fix_lost_divsqrt): New attribute.
	(in_branch_delay): Prevent div and sqrt in delay slot if
	fix_lost_divsqrt.
	* config/sparc/sparc.opt (sparc_fix_lost_divsqrt): New variable.

From-SVN: r255237