testsuite: Adjust pr96789.c to exclude vect_load_lanes

[Richard Sandiford]

"Kewen.Lin" <linkw@linux.ibm.com> writes:
> Hi Richard,
>
> Thanks for the review!
>
> on 2020/11/10 锟斤拷锟斤拷7:31, Richard Sandiford wrote:
>> "Kewen.Lin" <linkw@linux.ibm.com> writes:
>>> Hi,
>>>
>>> As Lyon pointed out, the newly introduced test case
>>> gcc.dg/tree-ssa/pr96789.c fails on arm-none-linux-gnueabihf.
>>> Loop vectorizer is able to vectorize the two loops which
>>> operate on array tmp with load_lanes feature support.  It
>>> makes dse3 get unexpected inputs and do nothing.
>>>
>>> This patch is to teach the case to respect vect_load_lanes,
>>> meanwhile to guard the check only under vect_int.
>> 
>> I'm not sure this is the right check.  The test passes on aarch64,
>> which also has load lanes, but apparently doesn't use them for this
>> test.  I think the way the loop vectoriser handles the loops will
>> depend a lot on target costs, which can vary in unpredictable ways.
>> 
>
> You are right, although aarch64 doesn't have this failure, it can fail
> with explicit -march=armv8-a+sve.  It can vary as target features/costs
> change.  The check is still fragile.
>
> Your suggestion with -ftree-slp-vectorize below is better!
>
>> Does it work if you instead change -ftree-vectorize to -ftree-slp-vectorize?
>> Or does that defeat the purpose of the test?
>
> It works, nice, thanks for the suggestion!
>
> I appended one explicit -fno-tree-loop-vectorize to avoid it to fail
> in case someone kicks off the testing with explicit -ftree-loop-vectorize.
>
> The updated version is pasted below, is it ok for trunk?

OK, thanks.

Richard

>
> BR,
> Kewen
> -----
> gcc/testsuite/ChangeLog:
>
> 	* gcc.dg/tree-ssa/pr96789.c: Adjusted by disabling loop vectorization.
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr96789.c b/gcc/testsuite/gcc.dg/tree-ssa/pr96789.c
> index d6139a014d8..5704952309b 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/pr96789.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr96789.c
> @@ -1,5 +1,8 @@
>  /* { dg-do compile } */
> -/* { dg-options "-O2 -funroll-loops -ftree-vectorize -fdump-tree-dse-details" } */
> +/* Disable loop vectorization to avoid that loop vectorizer
> +   optimizes those two loops that operate tmp array so that
> +   subsequent dse3 won't eliminate expected tmp stores.  */
> +/* { dg-options "-O2 -funroll-loops -ftree-slp-vectorize -fno-tree-loop-vectorize -fdump-tree-dse-details" } */
>
>  /* Test if scalar cleanup pass takes effects, mainly check
>     its secondary pass DSE can remove dead stores on array