[Patch v4 0/17] Add support for _Float16 to AArch64 and ARM

[James Greenhalgh]

Hi,

This patch set enables the _Float16 type specified in ISO/IEC TS 18661-3
for AArch64 and ARM. The patch set has been posted over the past two months,
with many of the target-independent changes approved. I'm reposting it in
entirity in the form I hope to commit it to trunk.

The patch set can be roughly split in three; first, hookization of
TARGET_FLT_EVAL_METHOD, and changes to the excess precision logic in the
compiler to handle the new values for FLT_EVAL_METHOD defined in
ISO/IEC TS-18661-3. Second, the AArch64 changes required to enable _Float16,
and finally the ARM changes required to enable _Float16.

The broad goals and an outline of each patch in the patch set were
described in https://gcc.gnu.org/ml/gcc-patches/2016-09/msg02383.html .
As compared to the original submission, the patch set has grown an ARM
port, and has had several rounds of technical review on the target
independent aspects.

This has resulted in many of the patches already being approved, a full
summary of the status of each ticket is immediately below.

Clearly the focus for review of this patch set now needs to be the AArch64
and ARM ports, I hope the appropriate maintainers will be able to do so in
time for the patch set to be accepted for GCC 7.

I've built and tested the full patch set on ARM (cross and native),
AArch64 (cross and native) and x86_64 (native) with no identified issues.

Thanks,
James

------------------
Target independent changes

10 patches, 9 previously approved, 1 New implementing testsuite
changes to enable _Float16 tests in more circumstances on ARM.
------------------

[Patch 1/17] Add a new target hook for describing excess precision intentions

  Approved: https://gcc.gnu.org/ml/gcc-patches/2016-11/msg00781.html

[Patch 2/17] Implement TARGET_C_EXCESS_PRECISION for i386

  Blanket approved by Jeff in:
    https://gcc.gnu.org/ml/gcc-patches/2016-09/msg02402.html

[Patch 3/17] Implement TARGET_C_EXCESS_PRECISION for s390

  Approved: https://gcc.gnu.org/ml/gcc-patches/2016-10/msg01554.html

[Patch 4/17] Implement TARGET_C_EXCESS_PRECISION for m68k

  Blanket approved by Jeff in:
    https://gcc.gnu.org/ml/gcc-patches/2016-09/msg02402.html
  And by Andreas: https://gcc.gnu.org/ml/gcc-patches/2016-09/msg02414.html

  There was a typo in the original patch, fixed in:
    https://gcc.gnu.org/ml/gcc-patches/2016-10/msg01173.html
  which I would apply as an "obvious" fix to the original patch.

[Patch 5/17] Add -fpermitted-flt-eval-methods=[c11|ts-18661-3]

  Approved: https://gcc.gnu.org/ml/gcc-patches/2016-09/msg02405.html

  Joseph had a comment in
  https://gcc.gnu.org/ml/gcc-patches/2016-10/msg00335.html that the tests
  should check FLT_EVAL_METHOD from <float.h> rather than
  __FLT_EVAL_METHOD__. Rather than implement that suggestion, I added tests
  to patch 6 which tested the <float.h> macro, and left the tests in this
  patch testing the internal macro.

[Patch 6/17] Migrate excess precision logic to use TARGET_EXCESS_PRECISION

  Approved (after removing a rebase bug):
  https://gcc.gnu.org/ml/gcc-patches/2016-11/msg00231.html

[Patch 7/17] Delete TARGET_FLT_EVAL_METHOD and poison it.

  Approved: https://gcc.gnu.org/ml/gcc-patches/2016-09/msg02401.html

[Patch 8/17] Make _Float16 available if HFmode is available

  Approved: https://gcc.gnu.org/ml/gcc-patches/2016-09/msg02403.html

[Patch libgcc 9/17] Update soft-fp from glibc

  Self approved under policy that we can update libraries which GCC mirrors
  without further approval.

[Patch testsuite patch 10/17] Add options for floatN when checking effective target for support

  NEW!

----------------
AArch64 changes

3 patches, none reviewed
----------------

[Patch AArch64 11/17] Add floatdihf2 and floatunsdihf2 patterns

  Not reviewed, last pinged (^6):
  https://gcc.gnu.org/ml/gcc-patches/2016-11/msg00584.html

[Patch libgcc AArch64 12/17] Enable hfmode soft-float conversions and truncations

  Not reviewed:
  https://gcc.gnu.org/ml/gcc-patches/2016-09/msg02395.html

[Patch AArch64 13/17] Enable _Float16 for AArch64

  Not reviewed:
  https://gcc.gnu.org/ml/gcc-patches/2016-10/msg01176.html

----------------
ARM changes

4 patches, none OK'ed
----------------
[Patch 14/17] [libgcc, ARM] Generalise float-to-half conversion function.

  Respun in this submission to avoid a bug identified during extended
  multilib testing, original submission here:
  https://gcc.gnu.org/ml/gcc-patches/2016-11/msg00714.html

[Patch 15/17 libgcc] Add double to half conversions.

  Reviewed, but not approved:
  https://gcc.gnu.org/ml/gcc-patches/2016-10/msg01975.html

  Changes were required to patch 16/17, and patch 10/17 was introduced to
  implement the suggested testsuite patch. The original patch still stands,
  and needs reviewed:
  https://gcc.gnu.org/ml/gcc-patches/2016-10/msg01914.html

[Patch 16/17 ARM] Half to double precision conversions

  Resubmitted: https://gcc.gnu.org/ml/gcc-patches/2016-11/msg00233.html
  Needs review.

[Patch ARM 17/17] Enable _Float16 for ARM.

  Resubmitted: https://gcc.gnu.org/ml/gcc-patches/2016-11/msg00234.html
  Needs review.