This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [PATCH PR81647][AARCH64][PING] Fix handling of Unordered Comparisons in aarch64-simd.md


PING

On 15/12/17 11:57, Sudakshina Das wrote:
Hi

This patch fixes the inconsistent behavior observed at -O3 for the unordered comparisons. According to the online docs (https://gcc.gnu.org/onlinedocs/gcc-7.2.0/gccint/Unary-and-Binary-Expressions.html), all of the following should not raise an FP exception:
- UNGE_EXPR
- UNGT_EXPR
- UNLE_EXPR
- UNLT_EXPR
- UNEQ_EXPR
Also ORDERED_EXPR and UNORDERED_EXPR should only return zero or one.

The aarch64-simd.md handling of these were generating exception raising instructions such as fcmgt. This patch changes the instructions that are emitted to in order to not give out the exceptions. We first check each operand for NaNs and force any elements containing NaN to zero before using them in the compare.

Example: UN<cc> (a, b) -> UNORDERED (a, b) | (cm<cc> (isnan (a) ? 0.0 : a, isnan (b) ? 0.0 : b))


The ORDERED_EXPR is now handled as (cmeq (a, a) & cmeq (b, b)) and UNORDERED_EXPR as ~ORDERED_EXPR and UNEQ as (~ORDERED_EXPR | cmeq (a,b)).

Testing done: Checked for regressions on bootstrapped aarch64-none-linux-gnu and added a new test case.

Is this ok for trunk? This will probably need a back-port to gcc-7-branch as well.

Thanks
Sudi

ChangeLog Entries:

*** gcc/ChangeLog ***

2017-12-15  Sudakshina Das  <sudi.das@arm.com>

     PR target/81647
    * config/aarch64/aarch64-simd.md (vec_cmp<mode><v_int_equiv>): Modify instructions for
     UNLT, UNLE, UNGT, UNGE, UNEQ, UNORDERED and ORDERED.

*** gcc/testsuite/ChangeLog ***

2017-12-15  Sudakshina Das  <sudi.das@arm.com>

     PR target/81647
     * gcc.target/aarch64/pr81647.c: New.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]