PHIOPT: Improve replace_phi_edge_with_variable's dce_ssa_names slightly

When I added the dce_ssa_names argument, I didn't realize bitmap was a
pointer so I used the default argument value as auto_bitmap(). But
instead we could just use nullptr and check if it was a nullptr
before calling simple_dce_from_worklist.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (replace_phi_edge_with_variable): Change
	the default argument value for dce_ssa_names to nullptr.
	Check to make sure dce_ssa_names is a non-nullptr before
	calling simple_dce_from_worklist.

diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index 51f33e1e81aaae85bc32d7891712da2fe044fa37..154a5abf86bb157d11255ba06a8e63c22cd572ea 100644 (file)
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -89,7 +89,7 @@ single_non_singleton_phi_for_edges (gimple_seq seq, edge e0, edge e1)
 static void
 replace_phi_edge_with_variable (basic_block cond_block,
                                edge e, gphi *phi, tree new_tree,
-                               bitmap dce_ssa_names = auto_bitmap())
+                               bitmap dce_ssa_names = nullptr)
 {
   basic_block bb = gimple_bb (phi);
   gimple_stmt_iterator gsi;
@@ -164,7 +164,8 @@ replace_phi_edge_with_variable (basic_block cond_block,
        gimple_cond_make_true (cond);
     }
 
-  simple_dce_from_worklist (dce_ssa_names);
+  if (dce_ssa_names)
+    simple_dce_from_worklist (dce_ssa_names);
 
   statistics_counter_event (cfun, "Replace PHI with variable", 1);