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

[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.

[Bug target/94154] 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

Bu Le <bule1 at huawei dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED

--- Comment #1 from Bu Le <bule1 at huawei dot com> ---
The patch has been reviewed and merged to master by Richard. Fixed and close.

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

[marxin at gcc dot gnu.org]

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

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marxin at gcc dot gnu.org

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
commit r10-7153-gdbf3dc75888623e9d4bb7cc5e9c30caa9b24ffe7
Author: Bu Le <bule1@huawei.com>
Date:   Thu Mar 12 22:39:12 2020 +0000

    aarch64: Add --params to control the number of recip steps [PR94154]

    -mlow-precision-div hard-coded the number of iterations to 2 for double
    and 1 for float.  This patch adds a --param to control the number.

    2020-03-13  Bu Le  <bule1@huawei.com>

    gcc/
            PR target/94154
            * config/aarch64/aarch64.opt (-param=aarch64-float-recp-precision=)
            (-param=aarch64-double-recp-precision=): New options.
            * doc/invoke.texi: Document them.
            * config/aarch64/aarch64.c (aarch64_emit_approx_div): Use them
            instead of hard-coding the choice of 1 for float and 2 for double.