[Bug target/94154] New: AArch64: Add parameters to tune the precision of reciprocal div

[bule1 at huawei dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94154

            Bug ID: 94154
           Summary: AArch64: Add parameters to tune the precision of
                    reciprocal div
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Keywords: patch
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bule1 at huawei dot com
                CC: richard.sandiford at arm dot com
  Target Milestone: ---
            Target: AARCH64

This report suggest to use parameters to control the number of newton
iterations when using the reciprocal division on aarch64 platform, which is
currently hard coded in aarch64.c. 

This can benefit some test cases in spec2017 fpspeed in peak mode that do not
have a high demand on precision. And also fix the downside that users are
forced to use  reciprocal approximation at low precision.  

A proposed patch is attached.