re PR c++/34949 (Dead code in empty destructors.)

	PR c++/34949
	PR c++/50243
	* tree-eh.c (optimize_clobbers): Only remove clobbers if bb doesn't
	contain anything but clobbers, at most one __builtin_stack_restore,
	optionally debug stmts and final resx, and if it has at least one
	incoming EH edge.  Don't check for SSA_NAME on LHS of a clobber.
	(sink_clobbers): Don't check for SSA_NAME on LHS of a clobber.
	Instead of moving clobbers with MEM_REF LHS with SSA_NAME address
	which isn't defaut definition, remove them.
	(unsplit_eh, cleanup_empty_eh): Use single_{pred,succ}_{p,edge}
	instead of EDGE_COUNT comparisons or EDGE_{PRED,SUCC}.
	* tree-ssa-ccp.c (execute_fold_all_builtins): Remove clobbers
	with MEM_REF LHS with SSA_NAME address.

	* g++.dg/opt/vt3.C: New test.
	* g++.dg/opt/vt4.C: New test.

From-SVN: r197580

1 files changed, 15 insertions, 0 deletions

diff --git a/gcc/tree-ssa-ccp.c b/gcc/tree-ssa-ccp.c
index a64bffc..f298b27 100644
--- a/gcc/tree-ssa-ccp.c
+++ b/gcc/tree-ssa-ccp.c
@@ -2396,6 +2396,21 @@ execute_fold_all_builtins (void)
 
           if (gimple_code (stmt) != GIMPLE_CALL)
 	    {
+	      /* Remove all *ssaname_N ={v} {CLOBBER}; stmts,
+		 after the last GIMPLE DSE they aren't needed and might
+		 unnecessarily keep the SSA_NAMEs live.  */
+	      if (gimple_clobber_p (stmt))
+		{
+		  tree lhs = gimple_assign_lhs (stmt);
+		  if (TREE_CODE (lhs) == MEM_REF
+		      && TREE_CODE (TREE_OPERAND (lhs, 0)) == SSA_NAME)
+		    {
+		      unlink_stmt_vdef (stmt);
+		      gsi_remove (&i, true);
+		      release_defs (stmt);
+		      continue;
+		    }
+		}
 	      gsi_next (&i);
 	      continue;
 	    }