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

[Sudakshina Das <sudi.das@arm.com>]

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.