On 01/03/2018 06:57 AM, Sudakshina Das wrote:
> Hi
>
> This patch add support for the missing transformation of (x | y) == x ->
> (y & ~x) == 0.
> The transformation for (x & y) == x case already exists in
> simplify-rtx.c since 2014 as of r218503 and this patch only adds a
> couple of extra patterns for the IOR case.
>
> Citing the example given in PR82439 :
>
> Simple testcase (f1 should generate the same as f2):
>
> int f1(int x, int y) { return (x | y) == x; }
> int f2(int x, int y) { return (y & ~x) == 0; }
>
> f1:
> orr w1, w0, w1
> cmp w1, w0
> cset w0, eq
> ret
> f2:
> bics wzr, w1, w0
> cset w0, eq
> ret
>
> This benefits targets that have the BICS instruction to generate better
> code. Wilco helped me in showing that even in targets that do not have
> the BICS instruction, this is no worse and gives out 2 instructions.
> For example in x86:
>
> 0000000000000000 <f1>:
> 0: 09 fe or %edi,%esi
> 2: 31 c0 xor %eax,%eax
> 4: 39 fe cmp %edi,%esi
> 6: 0f 94 c0 sete %al
> 9: c3 retq
>
> 0000000000000010 <f2>:
> 10: f7 d7 not %edi
> 12: 31 c0 xor %eax,%eax
> 14: 85 f7 test %esi,%edi
> 16: 0f 94 c0 sete %al
> 19: c3 retq
>
> Testing done: Checked for regressions on bootstrapped
> aarch64-none-linux-gnu and arm-none-linux-gnueabihf and added new test
> cases.
> Is this ok for trunk?
>
> Sudi
>
> ChangeLog Entries:
>
> *** gcc/ChangeLog ***
>
> 2017-01-03 Sudakshina Das <sudi....@arm.com>
>
> PR target/82439
> * simplify-rtx.c (simplify_relational_operation_1): Add
> simplifications of (x|y) == x for BICS pattern.
>
> *** gcc/testsuite/ChangeLog ***
>
> 2017-01-03 Sudakshina Das <sudi....@arm.com>
>
> PR target/82439
> * gcc.target/aarch64/bics_5.c: New test.
> * gcc.target/arm/bics_5.c: Likewise.
OK.
jeff
