Re: [PATCH] tree-optimization/106379 - add missing ~(a ^ b) folding for _Bool

[Richard Biener <rguenther@suse.de>]

> Am 22.07.2022 um 22:17 schrieb H.J. Lu via Gcc-patches <gcc-patches@gcc.gnu.org>:
> 
> On Thu, Jul 21, 2022 at 4:24 AM Richard Biener via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>> 
>> The following makes sure to fold ~(a ^ b) to a == b for truth
>> values (but not vectors, we'd have to check for vector support of
>> equality).  That turns the PR106379 testcase into a ranger one.
>> 
>> Note that while we arrive at ~(a ^ b) in a convoluted way from
>> original !a == !b one can eventually write the expression this
>> way directly as well.
>> 
>> Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
>> 
>>        PR tree-optimization/106379
>>        * match.pd (~(a ^ b) -> a == b): New pattern.
>> 
>>        * gcc.dg/pr106379-1.c: New testcase.
>> ---
>> gcc/match.pd                      | 6 ++++++
>> gcc/testsuite/gcc.dg/pr106379-1.c | 9 +++++++++
>> 2 files changed, 15 insertions(+)
>> create mode 100644 gcc/testsuite/gcc.dg/pr106379-1.c
>> 
>> diff --git a/gcc/match.pd b/gcc/match.pd
>> index 8bbc0dbd5cd..88a1a5aa9cc 100644
>> --- a/gcc/match.pd
>> +++ b/gcc/match.pd
>> @@ -1938,6 +1938,12 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>>  (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
>>   (bit_not (bit_xor (view_convert @0) @1))))
>> 
>> +/* ~(a ^ b) is a == b for truth valued a and b.  */
>> +(simplify
>> + (bit_not (bit_xor:s truth_valued_p@0 truth_valued_p@1))
>> + (if (!VECTOR_TYPE_P (type))
>> +  (convert (eq @0 @1))))
> 
> For integers, isn't it wrong to convert ~(boolean exp) to boolean exp?

That’s what the (convert. …) should compensate for?

Richard 

> 
>> /* (x & ~m) | (y & m) -> ((x ^ y) & m) ^ x */
>> (simplify
>>  (bit_ior:c (bit_and:cs @0 (bit_not @2)) (bit_and:cs @1 @2))
>> diff --git a/gcc/testsuite/gcc.dg/pr106379-1.c b/gcc/testsuite/gcc.dg/pr106379-1.c
>> new file mode 100644
>> index 00000000000..7f2575e02dc
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr106379-1.c
>> @@ -0,0 +1,9 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O -fdump-tree-forwprop1" } */
>> +
>> +_Bool foo (_Bool a, _Bool b)
>> +{
>> +  return !a == !b;
>> +}
>> +
>> +/* { dg-final { scan-tree-dump "\[ab\]_\[0-9\]+\\(D\\) == \[ba\]_\[0-9\]+\\(D\\)" "forwprop1" } } */
>> --
>> 2.35.3
> 
> 
> 
> --
> H.J.