[SVE] Fold svrev(svrev(v)) to v.

gcc/ChangeLog:
	* tree-ssa-forwprop.cc (is_combined_permutation_identity): Try to
	simplify two successive VEC_PERM_EXPRs with same VLA mask,
	where mask chooses elements in reverse order.

gcc/testsuite/ChangeLog:
	* gcc.target/aarch64/sve/acle/general/rev-1.c: New test.

2 files changed, 33 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/rev-1.c b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/rev-1.c
new file mode 100644
index 0000000..e57ee67
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/rev-1.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-optimized" } */
+
+#include <arm_sve.h>
+
+svint32_t f(svint32_t v)
+{
+  return svrev_s32 (svrev_s32 (v));
+}
+
+/* { dg-final { scan-tree-dump "return v_1\\(D\\)" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "VEC_PERM_EXPR" "optimized" } } */
diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 9b56744..9dc67b5 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -2541,6 +2541,27 @@ is_combined_permutation_identity (tree mask1, tree mask2)
 
   gcc_checking_assert (TREE_CODE (mask1) == VECTOR_CST
 		       && TREE_CODE (mask2) == VECTOR_CST);
+
+  /* For VLA masks, check for the following pattern:
+     v1 = VEC_PERM_EXPR (v0, ..., mask1)
+     v2 = VEC_PERM_EXPR (v1, ..., mask2)
+     -->
+     v2 = v0
+     if mask1 == mask2 == {nelts - 1, nelts - 2, ...}.  */
+
+  if (operand_equal_p (mask1, mask2, 0)
+      && !VECTOR_CST_NELTS (mask1).is_constant ())
+    {
+      vec_perm_builder builder;
+      if (tree_to_vec_perm_builder (&builder, mask1))
+	{
+	  poly_uint64 nelts = TYPE_VECTOR_SUBPARTS (TREE_TYPE (mask1));
+	  vec_perm_indices sel (builder, 1, nelts);
+	  if (sel.series_p (0, 1, nelts - 1, -1))
+	    return 1;
+	}
+    }
+
   mask = fold_ternary (VEC_PERM_EXPR, TREE_TYPE (mask1), mask1, mask1, mask2);
   if (mask == NULL_TREE || TREE_CODE (mask) != VECTOR_CST)
     return 0;