[AArch64] Fix for gcc-7 regression PR 80530

[Jakub Jelinek]

On Thu, Apr 27, 2017 at 01:32:11PM +0100, Richard Earnshaw (lists) wrote:
> This patch fixes the regression caused by the changes to add square root
> estimation when compiling for xgene-1 or exynos-m1 targets.
> 
> The issue is that the expand path for the reciprocal estimate square
> root pattern assumes that pattern cannot fail once it has been decided
> that this expansion path is available, but because the logic deep inside
> aarch64_emit_approx_sqrt() differs from use_rsqrt_p() the two disagree
> as to what is safe.
> 
> This patch refactors the logic to ensure that we cannot unknowingly make
> different choices here.
> 
> Bootstrap/testing completed ok.  I'll apply this to trunk.
> 
> Jakub: Are we having an RC2?  If so, is this ok for the gcc-7 branch?
> 
> 	PR target/80530
> 	* config/aarch64/aarch64.c (aarch64_emit_approx_sqrt): Ensure
> 	that the logic for permitting reciprocal estimates matches that
> 	in use_rsqrt_p.

No testcase?

We will have RC2 (later today or tomorrow), so I guess this is ok if you
believe it is important enough to have in 7.1 and very low risk.

	Jakub