[PATCH] Don't check can_vec_perm_const_p for nonlinear iv_init when it's constant.

[liuhongt via Gcc-patches]

When init_expr is INTEGER_CST or REAL_CST, can_vec_perm_const_p is not
necessary since there's no real vec_perm needed, but
vec_gen_perm_mask_checked will gcc_assert (can_vec_perm_const_p). So
it's better to use vec_gen_perm_mask_any in
vect_create_nonlinear_iv_init.

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

gcc/ChangeLog:

        PR tree-optimization/106963
        * tree-vect-loop.cc (vect_create_nonlinear_iv_init): Use
        vec_gen_perm_mask_any instead of vec_gen_perm_mask_check.

gcc/testsuite/ChangeLog:

        * gcc.target/i386/pr106963.c: New test.
---
 gcc/testsuite/gcc.target/i386/pr106963.c | 14 ++++++++++++++
 gcc/tree-vect-loop.cc                    |  5 ++++-
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr106963.c

diff --git a/gcc/testsuite/gcc.target/i386/pr106963.c 
b/gcc/testsuite/gcc.target/i386/pr106963.c
new file mode 100644
index 00000000000..9f2d20e2523
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr106963.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mavx -mno-avx2" } */
+
+void
+foo_neg_const (int *a)
+{
+  int i, b = 1;
+
+  for (i = 0; i < 1000; i++)
+    {
+      a[i] = b;
+      b = -b;
+    }
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 9c434b66c5b..aabdc6f2d81 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -8356,8 +8356,11 @@ vect_create_nonlinear_iv_init (gimple_seq* stmts, tree 
init_expr,
            sel[2 * i + 1] = i + nunits;
          }
        vec_perm_indices indices (sel, 2, nunits);
+       /* Don't use vect_gen_perm_mask_checked since can_vec_perm_const_p may
+          fail when vec_init is const vector. In that situation vec_perm is not
+          really needed.  */
        tree perm_mask_even
-         = vect_gen_perm_mask_checked (vectype, indices);
+         = vect_gen_perm_mask_any (vectype, indices);
        vec_init = gimple_build (stmts, VEC_PERM_EXPR,
                                 vectype,
                                 vec_init, vec_neg,
-- 
2.18.1