[PATCH] Fix PR49822

[Richard Guenther <rguenther at suse dot de>]

This robustifies remove_prop_source_from_use some more.

Bootstrapped and tested on x86_64-unknown-linux-gnu, also
cross-tested the arm testcase.  Applied.

Richard.

2011-07-25  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/49822
	* tree-ssa-forwprop.c (remove_prop_source_from_use): Robustify
	more.  Make sure to preserve stmts with side-effects.  Properly
	handle virtual defs, follow a longer def chain.

Index: gcc/tree-ssa-forwprop.c
===================================================================
*** gcc/tree-ssa-forwprop.c	(revision 176735)
--- gcc/tree-ssa-forwprop.c	(working copy)
*************** can_propagate_from (gimple def_stmt)
*** 295,303 ****
    return true;
  }
  
! /* Remove a copy chain ending in NAME along the defs.
     If NAME was replaced in its only use then this function can be used
!    to clean up dead stmts.  Returns true if cleanup-cfg has to run.  */
  
  static bool
  remove_prop_source_from_use (tree name)
--- 295,306 ----
    return true;
  }
  
! /* Remove a chain of dead statements starting at the definition of
!    NAME.  The chain is linked via the first operand of the defining statements.
     If NAME was replaced in its only use then this function can be used
!    to clean up dead stmts.  The function handles already released SSA
!    names gracefully.
!    Returns true if cleanup-cfg has to run.  */
  
  static bool
  remove_prop_source_from_use (tree name)
*************** remove_prop_source_from_use (tree name)
*** 309,327 ****
    do {
      basic_block bb;
  
!     if (!has_zero_uses (name))
        return cfg_changed;
  
      stmt = SSA_NAME_DEF_STMT (name);
!     bb = gimple_bb (stmt);
!     if (!bb)
        return cfg_changed;
      gsi = gsi_for_stmt (stmt);
!     release_defs (stmt);
      gsi_remove (&gsi, true);
      cfg_changed |= gimple_purge_dead_eh_edges (bb);
  
!     name = (gimple_assign_copy_p (stmt)) ? gimple_assign_rhs1 (stmt) : NULL;
    } while (name && TREE_CODE (name) == SSA_NAME);
  
    return cfg_changed;
--- 312,335 ----
    do {
      basic_block bb;
  
!     if (SSA_NAME_IN_FREE_LIST (name)
! 	|| SSA_NAME_IS_DEFAULT_DEF (name)
! 	|| !has_zero_uses (name))
        return cfg_changed;
  
      stmt = SSA_NAME_DEF_STMT (name);
!     if (gimple_code (stmt) == GIMPLE_PHI
! 	|| gimple_has_side_effects (stmt))
        return cfg_changed;
+ 
+     bb = gimple_bb (stmt);
      gsi = gsi_for_stmt (stmt);
!     unlink_stmt_vdef (stmt);
      gsi_remove (&gsi, true);
+     release_defs (stmt);
      cfg_changed |= gimple_purge_dead_eh_edges (bb);
  
!     name = is_gimple_assign (stmt) ? gimple_assign_rhs1 (stmt) : NULL_TREE;
    } while (name && TREE_CODE (name) == SSA_NAME);
  
    return cfg_changed;