forwprop: Change optimize_agr_copyprop into forward walk instead of backwards

While thinking about how to implement the rest of the copy prop and makes sure not
to introduce some compile time problems, optimize_agr_copyprop should be changed
into a forwproping rather than looking backwards.

Bootstrapped and tested on x86_64-linux-gnu.

gcc/ChangeLog:

	* tree-ssa-forwprop.cc (optimize_agr_copyprop): Change into a
	forward looking (looking at vdef's uses) instead of a back
	looking (vuse's def).

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

1 files changed, 60 insertions, 61 deletions

diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 43b1c9d..2dc77cc 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -1344,12 +1344,12 @@ optimize_memcpy_to_memset (gimple_stmt_iterator *gsip, tree dest, tree src, tree
   return true;
 }
 /* Optimizes
-   a = c;
-   b = a;
+   DEST = SRC;
+   DEST2 = DEST; # DEST2 = SRC2;
    into
-   a = c;
-   b = c;
-   GSIP is the second statement and SRC is the common
+   DEST = SRC;
+   DEST2 = SRC;
+   GSIP is the first statement and SRC is the common
    between the statements.
 */
 static bool
@@ -1365,65 +1365,64 @@ optimize_agr_copyprop (gimple_stmt_iterator *gsip)
   if (operand_equal_p (dest, src, 0))
     return false;
 
-  tree vuse = gimple_vuse (stmt);
-  /* If the vuse is the default definition, then there is no store beforehand.  */
-  if (SSA_NAME_IS_DEFAULT_DEF (vuse))
-    return false;
-  gimple *defstmt = SSA_NAME_DEF_STMT (vuse);
-  if (!gimple_assign_load_p (defstmt)
-      || !gimple_store_p (defstmt))
-    return false;
-  if (gimple_has_volatile_ops (defstmt))
-    return false;
-
-  tree dest2 = gimple_assign_lhs (defstmt);
-  tree src2 = gimple_assign_rhs1 (defstmt);
-
-  /* If the original store is `src2 = src2;` skip over it. */
-  if (operand_equal_p (src2, dest2, 0))
-    return false;
-  if (!operand_equal_p (src, dest2, 0))
-    return false;
-
-
-  /* For 2 memory refences and using a temporary to do the copy,
-     don't remove the temporary as the 2 memory references might overlap.
-     Note t does not need to be decl as it could be field.
-     See PR 22237 for full details.
-     E.g.
-     t = *a;
-     *b = t;
-     Cannot be convert into
-     t = *a;
-     *b = *a;
-     Though the following is allowed to be done:
-     t = *a;
-     *a = t;
-     And convert it into:
-     t = *a;
-     *a = *a;
-  */
-  if (!operand_equal_p (src2, dest, 0)
-      && !DECL_P (dest) && !DECL_P (src2))
-    return false;
-
-  if (dump_file && (dump_flags & TDF_DETAILS))
+  tree vdef = gimple_vdef (stmt);
+  imm_use_iterator iter;
+  gimple *use_stmt;
+  bool changed = false;
+  FOR_EACH_IMM_USE_STMT (use_stmt, iter, vdef)
     {
-      fprintf (dump_file, "Simplified\n  ");
-      print_gimple_stmt (dump_file, stmt, 0, dump_flags);
-      fprintf (dump_file, "after previous\n  ");
-      print_gimple_stmt (dump_file, defstmt, 0, dump_flags);
-    }
-  gimple_assign_set_rhs_from_tree (gsip, unshare_expr (src2));
-  update_stmt (stmt);
+      if (!gimple_assign_load_p (use_stmt)
+	  || !gimple_store_p (use_stmt))
+	continue;
+      if (gimple_has_volatile_ops (use_stmt))
+	continue;
+      tree dest2 = gimple_assign_lhs (use_stmt);
+      tree src2 = gimple_assign_rhs1 (use_stmt);
+      /* If the new store is `src2 = src2;` skip over it. */
+      if (operand_equal_p (src2, dest2, 0))
+	continue;
+      if (!operand_equal_p (dest, src2, 0))
+	continue;
+      /* For 2 memory refences and using a temporary to do the copy,
+	 don't remove the temporary as the 2 memory references might overlap.
+	 Note t does not need to be decl as it could be field.
+	 See PR 22237 for full details.
+	 E.g.
+	 t = *a; #DEST = SRC;
+	 *b = t; #DEST2 = SRC2;
+	 Cannot be convert into
+	 t = *a;
+	 *b = *a;
+	 Though the following is allowed to be done:
+	 t = *a;
+	 *a = t;
+	 And convert it into:
+	 t = *a;
+	 *a = *a;
+       */
+      if (!operand_equal_p (dest2, src, 0)
+	  && !DECL_P (dest2) && !DECL_P (src))
+	continue;
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "Simplified\n  ");
+	  print_gimple_stmt (dump_file, use_stmt, 0, dump_flags);
+	  fprintf (dump_file, "after previous\n  ");
+	  print_gimple_stmt (dump_file, stmt, 0, dump_flags);
+	}
+      gimple_stmt_iterator gsi = gsi_for_stmt (use_stmt);
+      gimple_assign_set_rhs_from_tree (&gsi, unshare_expr (src));
+      update_stmt (use_stmt);
 
-  if (dump_file && (dump_flags & TDF_DETAILS))
-    {
-      fprintf (dump_file, "into\n  ");
-      print_gimple_stmt (dump_file, stmt, 0, dump_flags);
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "into\n  ");
+	  print_gimple_stmt (dump_file, use_stmt, 0, dump_flags);
+	}
+      statistics_counter_event (cfun, "copy prop for aggregate", 1);
+      changed = true;
     }
-  statistics_counter_event (cfun, "copy prop for aggregate", 1);
-  return true;
+  return changed;
 }
 
 /* *GSI_P is a GIMPLE_CALL to a builtin function.