testsuite: Adjust pr96789.c to exclude vect_load_lanes

Kewen.Lin linkw@linux.ibm.com
Wed Nov 11 02:42:42 GMT 2020

Hi Richard,

Thanks for the review!

on 2020/11/10 下午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?


	* 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

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