[PATCH, ARM] Cortex-A9 MPCore volatile load workaround

[Chung-Lin Tang]

Hi Richard,
As we talked about earlier, here's a patch to add a compiler option to
work around Cortex-A9 MPCore errata 761319:
http://infocenter.arm.com/help/topic/com.arm.doc.uan0004a/UAN0004A_a9_read_read.pdf

What the option does basically, is to scan for volatile loads during
reorg, and add a dmb barrier after it. It also strives to make dmb
conditionally executed under TARGET_THUMB2, which means a new Thumb-2
specific *memory_barrier_t2 pattern in sync.md, with adjusted
conds/predicable attributes and %? in output strings.

Patch originally written by Julian, with additions by Meador, and
finally a few trivial adjustments by me. Again, we've been carrying this
fix for a release or two. Okay for trunk?

Thanks,
Chung-Lin

2014-06-09  Julian Brown  <julian@codesourcery.com>
            Meador Inge  <meadori@codesourcery.com>
            Chung-Lin Tang  <cltang@codesourcery.com>

	* config/arm/arm.c (arm_option_override): Emit warning if
	-mfix-cortex-a9-volatile-hazards is used on an incompatible CPU.
	(any_volatile_loads_p): New.
	(arm_cortex_a9_errata_reorg): New.
	(arm_reorg): Call arm_cortex_a9_errata_reorg.
	* config/arm/arm.opt (mfix-cortex-a9-volatile-hazards): Add
	option.
	* config/arm/sync.md (*memory_barrier): Don't use on Thumb-2.
	(*memory_barrier_t2): New, allow conditional execution on
	Thumb-2.
	* doc/invoke.texi (-mfix-cortex-a9-volatile-hazards): Add
	documentation.

        testsuite/
        * lib/target-supports.exp (check_effective_target_arm_dmb): New.
        * gcc.target/arm/a9-volatile-ordering-erratum-1.c: New test.
        * gcc.target/arm/a9-volatile-ordering-erratum-2.c: New test.
        * gcc.target/arm/a9-volatile-ordering-erratum-3.c: New test.
        * gcc.target/arm/a9-volatile-ordering-erratum-4.c: New test.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: a9-volatile-loads.patch
Type: text/x-patch
Size: 9511 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20140609/f2e66735/attachment.bin>