[gcc r13-2737] vect: Fix missed gather load opportunity

[gcc r13-2737] vect: Fix missed gather load opportunity

[Richard Sandiford]

https://gcc.gnu.org/g:4a773bf2f08656a39ac75cf6b4871c8cec8b5007

commit r13-2737-g4a773bf2f08656a39ac75cf6b4871c8cec8b5007
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Sep 20 15:27:46 2022 +0100

    vect: Fix missed gather load opportunity
    
    While writing a testcase for PR106794, I noticed that we failed
    to vectorise the testcase in the patch for SVE.  The code that
    recognises gather loads tries to optimise the point at which
    the offset is calculated, to avoid unnecessary extensions or
    truncations:
    
              /* Don't include the conversion if the target is happy with
                 the current offset type.  */
    
    But breaking only makes sense if we're at an SSA_NAME (which could
    then be vectorised).  We shouldn't break on a conversion embedded
    in a generic expression.
    
    gcc/
            * tree-vect-data-refs.cc (vect_check_gather_scatter): Restrict
            early-out optimisation to SSA_NAMEs.
    
    gcc/testsuite/
            * gcc.dg/vect/vect-gather-5.c: New test.

Diff:
---
 gcc/testsuite/gcc.dg/vect/vect-gather-5.c | 42 +++++++++++++++++++++++++++++++
 gcc/tree-vect-data-refs.cc                |  1 +
 2 files changed, 43 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/vect/vect-gather-5.c b/gcc/testsuite/gcc.dg/vect/vect-gather-5.c
new file mode 100644
index 00000000000..8b5074bba88
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-gather-5.c
@@ -0,0 +1,42 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O3" } */
+
+#ifdef __aarch64__
+#pragma GCC target "+sve"
+#endif
+
+long a[100], b[100], c[100];
+
+void g1 ()
+{
+  for (int i = 0; i < 100; i += 2)
+    {
+      c[i] += a[b[i]] + 1;
+      c[i + 1] += a[b[i + 1]] + 2;
+    }
+}
+
+long g2 ()
+{
+  long res = 0;
+  for (int i = 0; i < 100; i += 2)
+    {
+      res += a[b[i + 1]];
+      res += a[b[i]];
+    }
+  return res;
+}
+
+long g3 ()
+{
+  long res = 0;
+  for (int i = 0; i < 100; i += 2)
+    {
+      res += a[b[i]];
+      res += a[b[i + 1]];
+    }
+  return res;
+}
+
+/* { dg-final { scan-tree-dump-times {add new stmt[^\n]*GATHER_LOAD} 3 "vect" { target aarch64*-*-* } } } */
+/* { dg-final { scan-tree-dump-not {add new stmt[^\n]*VEC_PERM_EXPR} "vect" { target aarch64*-*-* } } } */
diff --git a/gcc/tree-vect-data-refs.cc b/gcc/tree-vect-data-refs.cc
index b279a82551e..e03b50498d1 100644
--- a/gcc/tree-vect-data-refs.cc
+++ b/gcc/tree-vect-data-refs.cc
@@ -4151,6 +4151,7 @@ vect_check_gather_scatter (stmt_vec_info stmt_info, loop_vec_info loop_vinfo,
 	  /* Don't include the conversion if the target is happy with
 	     the current offset type.  */
 	  if (use_ifn_p
+	      && TREE_CODE (off) == SSA_NAME
 	      && !POINTER_TYPE_P (TREE_TYPE (off))
 	      && vect_gather_scatter_fn_p (loop_vinfo, DR_IS_READ (dr),
 					   masked_p, vectype, memory_type,