[PATCH] Maintain single-use chains in forwprop better

[Richard Guenther]

This is another place where we fail to properly keep single-use
chains by leaving around dead code.  This confuses propagation
of comparisons which is restricted for non-single-uses.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2011-07-21  Richard Guenther  <rguent...@suse.de>

        * tree-ssa-forwprop.c (combine_conversions): Return whether
        we have to run cfg-cleanup.  Properly remove dead stmts.
        (ssa_forward_propagate_and_combine): Adjust.

Index: gcc/tree-ssa-forwprop.c
===================================================================
--- gcc/tree-ssa-forwprop.c.orig        2011-07-21 12:12:36.000000000 +0200
+++ gcc/tree-ssa-forwprop.c     2011-07-21 12:05:13.000000000 +0200
@@ -2136,9 +2136,10 @@ out:
 }
 
 /* Combine two conversions in a row for the second conversion at *GSI.
-   Returns true if there were any changes made.  */
+   Returns 1 if there were any changes made, 2 if cfg-cleanup needs to
+   run.  Else it returns 0.  */
  
-static bool
+static int
 combine_conversions (gimple_stmt_iterator *gsi)
 {
   gimple stmt = gsi_stmt (*gsi);
@@ -2155,15 +2156,15 @@ combine_conversions (gimple_stmt_iterato
   if (useless_type_conversion_p (TREE_TYPE (lhs), TREE_TYPE (op0)))
     {
       gimple_assign_set_rhs_code (stmt, TREE_CODE (op0));
-      return true;
+      return 1;
     }
 
   if (TREE_CODE (op0) != SSA_NAME)
-    return false;
+    return 0;
 
   def_stmt = SSA_NAME_DEF_STMT (op0);
   if (!is_gimple_assign (def_stmt))
-    return false;
+    return 0;
 
   if (CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt)))
     {
@@ -2202,7 +2203,7 @@ combine_conversions (gimple_stmt_iterato
          gimple_assign_set_rhs1 (stmt, unshare_expr (defop0));
          gimple_assign_set_rhs_code (stmt, TREE_CODE (defop0));
          update_stmt (stmt);
-         return true;
+         return remove_prop_source_from_use (op0) ? 2 : 1;
        }
 
       /* Likewise, if the intermediate and initial types are either both
@@ -2224,7 +2225,7 @@ combine_conversions (gimple_stmt_iterato
        {
          gimple_assign_set_rhs1 (stmt, defop0);
          update_stmt (stmt);
-         return true;
+         return remove_prop_source_from_use (op0) ? 2 : 1;
        }
 
       /* If we have a sign-extension of a zero-extended value, we can
@@ -2235,7 +2236,7 @@ combine_conversions (gimple_stmt_iterato
        {
          gimple_assign_set_rhs1 (stmt, defop0);
          update_stmt (stmt);
-         return true;
+         return remove_prop_source_from_use (op0) ? 2 : 1;
        }
 
       /* Two conversions in a row are not needed unless:
@@ -2264,7 +2265,7 @@ combine_conversions (gimple_stmt_iterato
        {
          gimple_assign_set_rhs1 (stmt, defop0);
          update_stmt (stmt);
-         return true;
+         return remove_prop_source_from_use (op0) ? 2 : 1;
        }
 
       /* A truncation to an unsigned type should be canonicalized as
@@ -2288,11 +2289,11 @@ combine_conversions (gimple_stmt_iterato
          else
            gimple_assign_set_rhs_from_tree (gsi, tem);
          update_stmt (gsi_stmt (*gsi));
-         return true;
+         return 1;
        }
     }
 
-  return false;
+  return 0;
 }
 
 /* Main entry point for the forward propagation and statement combine
@@ -2454,7 +2455,12 @@ ssa_forward_propagate_and_combine (void)
                else if (CONVERT_EXPR_CODE_P (code)
                         || code == FLOAT_EXPR
                         || code == FIX_TRUNC_EXPR)
-                 changed = combine_conversions (&gsi);
+                 {
+                   int did_something = combine_conversions (&gsi);
+                   if (did_something == 2)
+                     cfg_changed = true;
+                   changed = did_something != 0;
+                 }
                break;
              }