[gcc r12-5569] rs6000/test: Add emulated gather test case

[Kewen Lin <linkw@gcc.gnu.org>]

https://gcc.gnu.org/g:300dbea12693e365c89971527ca14cb0242def64

commit r12-5569-g300dbea12693e365c89971527ca14cb0242def64
Author: Kewen Lin <linkw@linux.ibm.com>
Date:   Sun Nov 28 19:59:59 2021 -0600

    rs6000/test: Add emulated gather test case
    
    As verified, the emulated gather capability of vectorizer
    (r12-2733) can help to speed up SPEC2017 510.parest_r on
    Power8/9/10 by 5% ~ 9% with option sets Ofast unroll and
    Ofast lto.
    
    This patch is to add a test case similar to the one in i386
    to add testing coverage for 510.parest_r hotspots.
    
    btw, different from the one in i386, this uses unsigned int
    as INDEXTYPE since the unpack support for unsigned int
    (r12-3134) also matters for the hotspots vectorization.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.target/powerpc/vect-gather-1.c: New test.

Diff:
---
 gcc/testsuite/gcc.target/powerpc/vect-gather-1.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/gcc/testsuite/gcc.target/powerpc/vect-gather-1.c b/gcc/testsuite/gcc.target/powerpc/vect-gather-1.c
new file mode 100644
index 00000000000..bf98045ab03
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/vect-gather-1.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* Profitable from Power8 since it supports efficient unaligned load.  */
+/* { dg-options "-Ofast -mdejagnu-cpu=power8 -fdump-tree-vect-details -fdump-tree-forwprop4" } */
+
+#ifndef INDEXTYPE
+#define INDEXTYPE unsigned int
+#endif
+double vmul(INDEXTYPE *rowstart, INDEXTYPE *rowend,
+	    double *luval, double *dst)
+{
+  double res = 0;
+  for (const INDEXTYPE * col = rowstart; col != rowend; ++col, ++luval)
+        res += *luval * dst[*col];
+  return res;
+}
+
+/* With gather emulation this should be profitable to vectorize from Power8.  */
+/* { dg-final { scan-tree-dump "loop vectorized" "vect" } } */
+/* The index vector loads and promotions should be scalar after forwprop.  */
+/* { dg-final { scan-tree-dump-not "vec_unpack" "forwprop4" } } */