[PATCH v6 6/8] Enable musttail tail conversion even when not optimizing

[Andi Kleen <ak@linux.intel.com>]

Enable the tailcall optimization for non optimizing builds,
but in this case only checks calls that have the musttail attribute set.
This makes musttail work without optimization.

This is done with a new late musttail pass that is only active when
not optimizing. The pass must be after ehcleanup.

gcc/ChangeLog:

	* passes.def (pass_musttail): Add.
	* tree-pass.h (make_pass_musttail): Add.
	* tree-tailcall.cc (find_tail_calls): Handle only_musttail
	  argument.
	(tree_optimize_tail_calls_1): Pass on only_musttail.
	(execute_tail_calls): Pass only_musttail as false.
	(class pass_musttail): Add.
	(make_pass_musttail): Add.
---
 gcc/passes.def       |  1 +
 gcc/tree-pass.h      |  1 +
 gcc/tree-tailcall.cc | 64 +++++++++++++++++++++++++++++++++++++-------
 3 files changed, 57 insertions(+), 9 deletions(-)

diff --git a/gcc/passes.def b/gcc/passes.def
index 1cbbd4130970..3e83cc327fd2 100644
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -443,6 +443,7 @@ along with GCC; see the file COPYING3.  If not see
   NEXT_PASS (pass_tsan_O0);
   NEXT_PASS (pass_sanopt);
   NEXT_PASS (pass_cleanup_eh);
+  NEXT_PASS (pass_musttail);
   NEXT_PASS (pass_lower_resx);
   NEXT_PASS (pass_nrv);
   NEXT_PASS (pass_gimple_isel);
diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
index 29267589eeb3..0668cea0a48e 100644
--- a/gcc/tree-pass.h
+++ b/gcc/tree-pass.h
@@ -368,6 +368,7 @@ extern gimple_opt_pass *make_pass_sra (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_sra_early (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_tail_recursion (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_tail_calls (gcc::context *ctxt);
+extern gimple_opt_pass *make_pass_musttail (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_fix_loops (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_tree_loop (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_tree_no_loop (gcc::context *ctxt);
diff --git a/gcc/tree-tailcall.cc b/gcc/tree-tailcall.cc
index e9f7f8a12b3a..094856de22ef 100644
--- a/gcc/tree-tailcall.cc
+++ b/gcc/tree-tailcall.cc
@@ -408,10 +408,10 @@ static live_vars_map *live_vars;
 static vec<bitmap_head> live_vars_vec;
 
 /* Finds tailcalls falling into basic block BB. The list of found tailcalls is
-   added to the start of RET.  */
+   added to the start of RET. When ONLY_MUSTTAIL is set only handle musttail.  */
 
 static void
-find_tail_calls (basic_block bb, struct tailcall **ret)
+find_tail_calls (basic_block bb, struct tailcall **ret, bool only_musttail)
 {
   tree ass_var = NULL_TREE, ret_var, func, param;
   gimple *stmt;
@@ -445,6 +445,9 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
       if (is_gimple_call (stmt))
 	{
 	  call = as_a <gcall *> (stmt);
+	  /* Handle only musttail calls when not optimizing.  */
+	  if (only_musttail && !gimple_call_must_tail_p (call))
+	    return;
 	  ass_var = gimple_call_lhs (call);
 	  break;
 	}
@@ -467,7 +470,7 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
       edge_iterator ei;
       /* Recurse to the predecessors.  */
       FOR_EACH_EDGE (e, ei, bb->preds)
-	find_tail_calls (e->src, ret);
+	find_tail_calls (e->src, ret, only_musttail);
 
       return;
     }
@@ -528,7 +531,8 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
   func = gimple_call_fndecl (call);
   if (func
       && !fndecl_built_in_p (func)
-      && recursive_call_p (current_function_decl, func))
+      && recursive_call_p (current_function_decl, func)
+      && !only_musttail)
     {
       tree arg;
 
@@ -1094,10 +1098,11 @@ create_tailcall_accumulator (const char *label, basic_block bb, tree init)
 }
 
 /* Optimizes tail calls in the function, turning the tail recursion
-   into iteration.  */
+   into iteration. When ONLY_MUSTCALL is true only optimize mustcall
+   marked calls.  */
 
 static unsigned int
-tree_optimize_tail_calls_1 (bool opt_tailcalls)
+tree_optimize_tail_calls_1 (bool opt_tailcalls, bool only_mustcall)
 {
   edge e;
   bool phis_constructed = false;
@@ -1117,7 +1122,7 @@ tree_optimize_tail_calls_1 (bool opt_tailcalls)
       /* Only traverse the normal exits, i.e. those that end with return
 	 statement.  */
       if (safe_is_a <greturn *> (*gsi_last_bb (e->src)))
-	find_tail_calls (e->src, &tailcalls);
+	find_tail_calls (e->src, &tailcalls, only_mustcall);
     }
 
   if (live_vars)
@@ -1228,7 +1233,7 @@ gate_tail_calls (void)
 static unsigned int
 execute_tail_calls (void)
 {
-  return tree_optimize_tail_calls_1 (true);
+  return tree_optimize_tail_calls_1 (true, false);
 }
 
 namespace {
@@ -1261,7 +1266,7 @@ public:
   bool gate (function *) final override { return gate_tail_calls (); }
   unsigned int execute (function *) final override
     {
-      return tree_optimize_tail_calls_1 (false);
+      return tree_optimize_tail_calls_1 (false, false);
     }
 
 }; // class pass_tail_recursion
@@ -1312,3 +1317,44 @@ make_pass_tail_calls (gcc::context *ctxt)
 {
   return new pass_tail_calls (ctxt);
 }
+
+namespace {
+
+const pass_data pass_data_musttail =
+{
+  GIMPLE_PASS, /* type */
+  "musttail", /* name */
+  OPTGROUP_NONE, /* optinfo_flags */
+  TV_NONE, /* tv_id */
+  ( PROP_cfg | PROP_ssa ), /* properties_required */
+  0, /* properties_provided */
+  0, /* properties_destroyed */
+  0, /* todo_flags_start */
+  0, /* todo_flags_finish */
+};
+
+class pass_musttail : public gimple_opt_pass
+{
+public:
+  pass_musttail (gcc::context *ctxt)
+    : gimple_opt_pass (pass_data_musttail, ctxt)
+  {}
+
+  /* opt_pass methods: */
+  /* This pass is only used when not optimizing to make [[musttail]] still
+     work.  */
+  bool gate (function *) final override { return !flag_optimize_sibling_calls; }
+  unsigned int execute (function *) final override
+  {
+    return tree_optimize_tail_calls_1 (true, true);
+  }
+
+}; // class pass_musttail
+
+} // anon namespace
+
+gimple_opt_pass *
+make_pass_musttail (gcc::context *ctxt)
+{
+  return new pass_musttail (ctxt);
+}
-- 
2.44.0