[Bug tree-optimization/100382] [12 Regression] go.test/test/fixedbugs/issue16095.go hang since r12-248

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100382

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
With the following patch this "issue" would show.  Not sure why we think
a postdom walk is appropriate for DSE rather than a reverse program order one.

diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index aecf6ab8c46..5bb5adf43c6 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -39,6 +39,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "builtins.h"
 #include "gimple-fold.h"
 #include "gimplify.h"
+#include "cfganal.h"

 /* This file implements dead store elimination.

@@ -1280,7 +1281,16 @@ pass_dse::execute (function *fun)
   /* Dead store elimination is fundamentally a walk of the post-dominator
      tree and a backwards walk of statements within each block.  */
   dse_dom_walker walker (CDI_POST_DOMINATORS);
-  walker.walk (fun->cfg->x_exit_block_ptr);
+  //walker.walk (fun->cfg->x_exit_block_ptr);
+  int *rpo = XNEWVEC (int, n_basic_blocks_for_fn (fun) - NUM_FIXED_BLOCKS);
+  auto_bitmap exits;
+  edge entry = single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (fun));
+  bitmap_set_bit (exits, EXIT_BLOCK);
+  int n = rev_post_order_and_mark_dfs_back_seme
+    (fun, entry, exits, true, rpo, NULL);
+  for (int i = n; i != 0; --i)
+    walker.before_dom_children (BASIC_BLOCK_FOR_FN (fun, rpo[i-1]));
+  free (rpo);
   free_dominance_info (CDI_POST_DOMINATORS);

   unsigned todo = walker.todo ();