[V2/PATCH] Fix tree-optimization/102216: missed optimization causing Warray-bounds

[<apinski@marvell.com>]

From: Andrew Pinski <apinski@marvell.com>

The problem here is tree-ssa-forwprop.c likes to produce
&MEM <const char *> [(void *)_4 + 152B] which is the same as
_4 p+ 152 which the rest of GCC likes better.
This implements this transformation back to pointer plus to
improve better code generation later on.

OK? Bootstrapped and tested on aarch64-linux-gnu.

Changes from v1:
* v2: Add comments.

gcc/ChangeLog:

	PR tree-optimization/102216
	* tree-ssa-forwprop.c (rewrite_assign_addr): New function.
	(forward_propagate_addr_expr_1): Use rewrite_assign_addr
	when rewriting into the addr_expr into an assignment.

gcc/testsuite/ChangeLog:

	PR tree-optimization/102216
	* g++.dg/tree-ssa/pr102216.C: New test.
---
 gcc/testsuite/g++.dg/tree-ssa/pr102216.C | 22 +++++++++
 gcc/tree-ssa-forwprop.c                  | 58 ++++++++++++++++++------
 2 files changed, 67 insertions(+), 13 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr102216.C

diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr102216.C b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
new file mode 100644
index 00000000000..b903e4eb57d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C
@@ -0,0 +1,22 @@
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+void link_error ();
+void g ()
+{
+  const char **language_names;
+
+  language_names = new const char *[6];
+
+  const char **language_names_p = language_names;
+
+  language_names_p++;
+  language_names_p++;
+  language_names_p++;
+
+  if ( (language_names_p) - (language_names+3) != 0)
+    link_error();
+  delete[] language_names;
+}
+/* We should have removed the link_error on the gimple level as GCC should
+   be able to tell that language_names_p is the same as language_names+3.  */
+/* { dg-final { scan-tree-dump-times "link_error" 0 "optimized" } } */
+
diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
index a830bab78ba..e4331c60525 100644
--- a/gcc/tree-ssa-forwprop.c
+++ b/gcc/tree-ssa-forwprop.c
@@ -637,6 +637,47 @@ forward_propagate_into_cond (gimple_stmt_iterator *gsi_p)
   return 0;
 }
 
+/* Rewrite the DEF_RHS as needed into the (plain) use statement.  */
+
+static void
+rewrite_assign_addr (gimple_stmt_iterator *use_stmt_gsi, tree def_rhs)
+{
+  tree def_rhs_base;
+  poly_int64 def_rhs_offset;
+
+  /* Get the base and offset.  */
+  if ((def_rhs_base = get_addr_base_and_unit_offset (TREE_OPERAND (def_rhs, 0),
+						     &def_rhs_offset)))
+    {
+      tree new_ptr;
+      poly_offset_int off = 0;
+
+      /* If the base was a MEM, then add the offset to the other
+         offset and adjust the base. */
+      if (TREE_CODE (def_rhs_base) == MEM_REF)
+	{
+	  off += mem_ref_offset (def_rhs_base);
+	  new_ptr = TREE_OPERAND (def_rhs_base, 0);
+	}
+      else
+	new_ptr = build_fold_addr_expr (def_rhs_base);
+
+      /* If we have the new base is not an address express, then use a p+ expression
+         as the new expression instead of &MEM[x, offset]. */
+      if (TREE_CODE (new_ptr) != ADDR_EXPR)
+	{
+	  tree offset = wide_int_to_tree (sizetype, off);
+	  def_rhs = build2 (POINTER_PLUS_EXPR, TREE_TYPE (def_rhs), new_ptr, offset);
+	}
+    }
+
+  /* Replace the rhs with the new expression.  */
+  def_rhs = unshare_expr (def_rhs);
+  gimple_assign_set_rhs_from_tree (use_stmt_gsi, def_rhs);
+  gimple *use_stmt = gsi_stmt (*use_stmt_gsi);
+  update_stmt (use_stmt);
+}
+
 /* We've just substituted an ADDR_EXPR into stmt.  Update all the
    relevant data structures to match.  */
 
@@ -696,8 +737,8 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
       if (single_use_p
 	  && useless_type_conversion_p (TREE_TYPE (lhs), TREE_TYPE (def_rhs)))
 	{
-	  gimple_assign_set_rhs1 (use_stmt, unshare_expr (def_rhs));
-	  gimple_assign_set_rhs_code (use_stmt, TREE_CODE (def_rhs));
+	  rewrite_assign_addr (use_stmt_gsi, def_rhs);
+	  gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
 	  return true;
 	}
 
@@ -741,14 +782,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
       if (forward_propagate_addr_expr (lhs, new_def_rhs, single_use_p))
 	return true;
 
-      if (useless_type_conversion_p (TREE_TYPE (lhs),
-				     TREE_TYPE (new_def_rhs)))
-	gimple_assign_set_rhs_with_ops (use_stmt_gsi, TREE_CODE (new_def_rhs),
-					new_def_rhs);
-      else if (is_gimple_min_invariant (new_def_rhs))
-	gimple_assign_set_rhs_with_ops (use_stmt_gsi, NOP_EXPR, new_def_rhs);
-      else
-	return false;
+      rewrite_assign_addr (use_stmt_gsi, new_def_rhs);
       gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt);
       update_stmt (use_stmt);
       return true;
@@ -951,9 +985,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
 					      unshare_expr (def_rhs),
 					      fold_convert (ptr_type_node,
 							    rhs2)));
-      gimple_assign_set_rhs_from_tree (use_stmt_gsi, new_rhs);
-      use_stmt = gsi_stmt (*use_stmt_gsi);
-      update_stmt (use_stmt);
+      rewrite_assign_addr (use_stmt_gsi, new_rhs);
       tidy_after_forward_propagate_addr (use_stmt);
       return true;
     }
-- 
2.17.1