[PATCH][match-and-simplify] Change back default behavior of fold_stmt

[Richard Biener]

This changes default behavior of fold_stmt back to _not_ following
SSA use-def chains when trying to simplify things.  I had to force
that already for one caller and for the merge to trunk I'd rather
not track down issues in every other existing caller.

This means that fold_stmt will not become more powerful, at least for now.
I still hope to get rid of its use of fold() during the merge process.

Bootstrap and regtest ongoing on x86_64-unknown-linux-gnu.

(yeah, I'm preparing a first batch of changes to merge from the
branch)

Richard.

2014-10-14  Richard Biener  <rguenther@suse.de>

	* gimple-fold.c (fold_stmt): Make old API never follow SSA edges
	when simplifying.
	(no_follow_ssa_edges): New function.
	* tree-cfg.c (no_follow_ssa_edges): Remove.
	(replace_uses_by): Use plain fold_stmt again.

Index: gcc/gimple-fold.c
===================================================================
--- gcc/gimple-fold.c	(revision 216146)
+++ gcc/gimple-fold.c	(working copy)
@@ -3136,6 +3136,14 @@ fail:
   return changed;
 }
 
+/* Valueziation callback that ends up not following SSA edges.  */
+
+static tree
+no_follow_ssa_edges (tree)
+{
+  return NULL_TREE;
+}
+
 /* Fold the statement pointed to by GSI.  In some cases, this function may
    replace the whole statement with a new one.  Returns true iff folding
    makes any changes.
@@ -3146,7 +3154,7 @@ fail:
 bool
 fold_stmt (gimple_stmt_iterator *gsi)
 {
-  return fold_stmt_1 (gsi, false, NULL);
+  return fold_stmt_1 (gsi, false, no_follow_ssa_edges);
 }
 
 bool
@@ -3167,7 +3175,7 @@ bool
 fold_stmt_inplace (gimple_stmt_iterator *gsi)
 {
   gimple stmt = gsi_stmt (*gsi);
-  bool changed = fold_stmt_1 (gsi, true, NULL);
+  bool changed = fold_stmt_1 (gsi, true, no_follow_ssa_edges);
   gcc_assert (gsi_stmt (*gsi) == stmt);
   return changed;
 }
Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c	(revision 216146)
+++ gcc/tree-cfg.c	(working copy)
@@ -1709,14 +1709,6 @@ gimple_can_merge_blocks_p (basic_block a
   return true;
 }
 
-/* ???  Maybe this should be a generic overload of fold_stmt.  */
-
-static tree
-no_follow_ssa_edges (tree)
-{
-  return NULL_TREE;
-}
-
 /* Replaces all uses of NAME by VAL.  */
 
 void
@@ -1773,17 +1765,7 @@ replace_uses_by (tree name, tree val)
 		  recompute_tree_invariant_for_addr_expr (op);
 	      }
 
-	  /* If we have sth like
-	       neighbor_29 = <name> + -1;
-	       _33 = <name> + neighbor_29;
-	     and substitute 1 for <name> then when visiting
-	     _33 first then folding will simplify the stmt
-	     to _33 = <name>; and the new immediate use will
-	     be inserted before the stmt iterator marker and
-	     thus we fail to visit it again, ICEing within the
-	     has_zero_uses assert.
-	     Avoid that by never following SSA edges.  */
-	  if (fold_stmt (&gsi, no_follow_ssa_edges))
+	  if (fold_stmt (&gsi))
 	    stmt = gsi_stmt (gsi);
 
 	  if (maybe_clean_or_replace_eh_stmt (orig_stmt, stmt))