Re: [PATCH-v3] [SPARC] Add a workaround for the LEON3FT store-store errata

[Eric Botcazou <ebotcazou@adacore.com>]

> This patch adds a workaround to the Sparc backend for the LEON3FT
> store-store errata. It is enabled when using the -mfix-ut699,
> -mfix-ut700, or -mfix-gr712rc flag.

Let's forget -mfix-gr712rc for now, -mfix-ut700 is enough I think.

> The workaround inserts NOP instructions to prevent the following two
> instruction sequences from being generated:
> 
> std -> stb/sth/st/std
> stb/sth/st -> any single non-store/load instruction -> stb/sth/st/std
> 
> The __FIX_B2BST define can be used to only enable workarounds in assembly
> code when the flag is used.

I'm not thrilled with this, it's undocumented, the other workaround don't have 
it and I don't think that we really need it.

> See GRLIB-TN-0009, "LEON3FT Stale Cache Entry After Store with Data Tag
> Parity Error", for more information.
> 
> gcc/ChangeLog:
> 
> 2017-06-21  Daniel Cederman  <cederman@gaisler.com>
> 
> 	* config/sparc/sparc.c (sparc_do_work_around_errata): Insert NOP
> 	instructions to prevent sequences that can trigger the store-store
> 	errata for certain LEON3FT processors.
> 	(sparc_option_override): -mfix-ut699, -mfix-ut700, and
> 	-mfix-gr712rc enables the errata workaround.
> 	* config/sparc/sparc-c.c (sparc_target_macros): Define __FIX_B2BST
> 	when errata workaround is enabled.
> 	* config/sparc/sparc.md: Prevent stores in delay slot.
> 	* config/sparc/sparc.opt: Add -mfix-ut700 and -mfix-gr712rc flag.
> 	* doc/invoke.texi: Document -mfix-ut700 and -mfix-gr712rc flag.

OK for mainline and 7 branch modulo the above two remarks.

-- 
Eric Botcazou