[PATCH] For datarefs with big gap, split them into different groups.

[liuhongt]

The patch tries to solve miss vectorization for below case.

void
foo (int* a, int* restrict b)
{
    b[0] = a[0] * a[64];
    b[1] = a[65] * a[1];
    b[2] = a[2] * a[66];
    b[3] = a[67] * a[3];
    b[4] = a[68] * a[4];
    b[5] = a[69] * a[5];
    b[6] = a[6] * a[70];
    b[7] = a[7] * a[71];
}

In vect_analyze_data_ref_accesses, a[0], a[1], .. a[7], a[64], ...,
a[71] are in same group with size of 71. It caused vectorization
unprofitable.

Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
Ok for trunk?

gcc/ChangeLog:

        * tree-vect-data-refs.cc (vect_analyze_data_ref_accesses):
        Split datarefs when there's a gap bigger than
        MAX_BITSIZE_MODE_ANY_MODE.

gcc/testsuite/ChangeLog:

        * gcc.dg/vect/bb-slp-pr119181.c: New test.
---
 gcc/testsuite/gcc.dg/vect/bb-slp-pr119181.c | 15 +++++++++++++++
 gcc/tree-vect-data-refs.cc                  |  6 ++++++
 2 files changed, 21 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-pr119181.c

diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr119181.c 
b/gcc/testsuite/gcc.dg/vect/bb-slp-pr119181.c
new file mode 100644
index 00000000000..b0d3e5a3cb8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr119181.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+void
+foo (int* a, int* restrict b)
+{
+    b[0] = a[0] * a[64];
+    b[1] = a[65] * a[1];
+    b[2] = a[2] * a[66];
+    b[3] = a[67] * a[3];
+    b[4] = a[68] * a[4];
+    b[5] = a[69] * a[5];
+    b[6] = a[6] * a[70];
+    b[7] = a[7] * a[71];
+}
+
+/* { dg-final { scan-tree-dump-times "optimized: basic block" 1 "slp2" { 
target vect_int_mult } } } */
diff --git a/gcc/tree-vect-data-refs.cc b/gcc/tree-vect-data-refs.cc
index 9fd1ef29650..387e8ac8b61 100644
--- a/gcc/tree-vect-data-refs.cc
+++ b/gcc/tree-vect-data-refs.cc
@@ -3657,6 +3657,12 @@ vect_analyze_data_ref_accesses (vec_info *vinfo,
                      && init_a <= init_prev
                      && init_prev <= init_b);
 
+         /* For datarefs with big gap, it's better to split them into different
+            groups.
+            .i.e a[0], a[1], a[2], .. a[7], a[100], a[101],..., a[107]  */
+         if ((unsigned HOST_WIDE_INT)(init_b - init_prev) * tree_to_uhwi (szb)
+             > MAX_BITSIZE_MODE_ANY_MODE / BITS_PER_UNIT)
+           break;
          /* Do not place the same access in the interleaving chain twice.  */
          if (init_b == init_prev)
            {
-- 
2.34.1