tree-optimization/99912 - schedule another TODO_remove_unused_locals

This makes sure to remove unused locals and prune CLOBBERs after
the first scalar cleanup phase after IPA optimizations.  On the
testcase in the PR this results in 8000 CLOBBERs removed which
in turn unleashes more DSE which otherwise hits its walking limit
of 256 too early on this testcase.

2021-04-27  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/99912
	* passes.def: Add comment about new TODO_remove_unused_locals.
	* tree-stdarg.c (pass_data_stdarg): Run TODO_remove_unused_locals
	at start.

diff --git a/gcc/passes.def b/gcc/passes.def
index 61fe9fd..f7c4289 100644 (file)
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -212,6 +212,9 @@ along with GCC; see the file COPYING3.  If not see
       NEXT_PASS (pass_vrp, true /* warn_array_bounds_p */);
       NEXT_PASS (pass_dse);
       NEXT_PASS (pass_dce);
+      /* pass_stdarg is always run and at this point we execute
+         TODO_remove_unused_locals to prune CLOBBERs of dead
+        variables which are otherwise a churn on alias walkings.  */
       NEXT_PASS (pass_stdarg);
       NEXT_PASS (pass_call_cdce);
       NEXT_PASS (pass_cselim);

diff --git a/gcc/tree-stdarg.c b/gcc/tree-stdarg.c
index ef21c12..2f77a61 100644 (file)
--- a/gcc/tree-stdarg.c
+++ b/gcc/tree-stdarg.c
@@ -1114,7 +1114,7 @@ const pass_data pass_data_stdarg =
   ( PROP_cfg | PROP_ssa ), /* properties_required */
   PROP_gimple_lva, /* properties_provided */
   0, /* properties_destroyed */
-  0, /* todo_flags_start */
+  TODO_remove_unused_locals, /* todo_flags_start */
   0, /* todo_flags_finish */
 };