[PATCH, ARM] Work around erratum in VFP9

[Richard Earnshaw <rearnsha at arm dot com>]

The VFP9 floating-point unit (as occasionally used with ARM9 devices)
has an erratum (760019) whereby it is possible for floating-point
division and square-root instructions to be executed twice.  This is not
a problem if the destination register is not used as an input, but can
cause incorrect results if they do.

The safest work-around for this issue is to make the compiler treat
these instructions as early-clobber; this ensures that the conditions
for result corruption cannot occur.

This patch takes that approach, but relaxes back to the original
behaviour when either the architecture level is ARMv6 or higher or the
VFP sub-architecture level is VFPv3 or higher; if either of these are
true then the code cannot run on an affected part.

2014-07-03  Richard Earnshaw  <rearnsha@arm.com>

	* arm.md (arch): Add armv6_or_vfpv3.
	(arch_enabled): Add test for the above.
	* vfp.md (divsf_vfp, divdf_vfp): Add earlyclobber when code can run
	on VFP9.
	(sqrtsf_vfp, sqrtdf_vfp): Likewise.

Committed to trunk.

R.

Attachment: vfp-760019.patch
Description: Text document