[PATCH v8 07/12] Enable musttail tail conversion even when not optimizing
Andi Kleen
ak@linux.intel.com
Sat Jun 22 18:54:39 GMT 2024
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 new pass relies on tree-cfg to discover musttails.
This avoids a ~0.8% compiler run time penalty at -O0.
gcc/ChangeLog:
* function.h (struct function): Add has_musttail.
* lto-streamer-in.cc (input_struct_function_base): Stream
has_musttail.
* lto-streamer-out.cc (output_struct_function_base): Dito.
* passes.def (pass_musttail): Add.
* tree-cfg.cc (notice_special_calls): Record has_musttail.
(clear_special_calls): Clear has_musttail.
* 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/function.h | 3 ++
gcc/lto-streamer-in.cc | 1 +
gcc/lto-streamer-out.cc | 1 +
gcc/passes.def | 1 +
gcc/tree-cfg.cc | 3 ++
gcc/tree-pass.h | 1 +
gcc/tree-tailcall.cc | 66 +++++++++++++++++++++++++++++++++++------
7 files changed, 67 insertions(+), 9 deletions(-)
diff --git a/gcc/function.h b/gcc/function.h
index c0ba6cc1531a..fbeadeaf4104 100644
--- a/gcc/function.h
+++ b/gcc/function.h
@@ -430,6 +430,9 @@ struct GTY(()) function {
/* Nonzero when the tail call has been identified. */
unsigned int tail_call_marked : 1;
+ /* Has musttail marked calls. */
+ unsigned int has_musttail : 1;
+
/* Nonzero if the current function contains a #pragma GCC unroll. */
unsigned int has_unroll : 1;
diff --git a/gcc/lto-streamer-in.cc b/gcc/lto-streamer-in.cc
index ad0ca24007a0..2e592be80823 100644
--- a/gcc/lto-streamer-in.cc
+++ b/gcc/lto-streamer-in.cc
@@ -1325,6 +1325,7 @@ input_struct_function_base (struct function *fn, class data_in *data_in,
fn->calls_eh_return = bp_unpack_value (&bp, 1);
fn->has_force_vectorize_loops = bp_unpack_value (&bp, 1);
fn->has_simduid_loops = bp_unpack_value (&bp, 1);
+ fn->has_musttail = bp_unpack_value (&bp, 1);
fn->assume_function = bp_unpack_value (&bp, 1);
fn->va_list_fpr_size = bp_unpack_value (&bp, 8);
fn->va_list_gpr_size = bp_unpack_value (&bp, 8);
diff --git a/gcc/lto-streamer-out.cc b/gcc/lto-streamer-out.cc
index d4f728094ed5..0be381abbd96 100644
--- a/gcc/lto-streamer-out.cc
+++ b/gcc/lto-streamer-out.cc
@@ -2290,6 +2290,7 @@ output_struct_function_base (struct output_block *ob, struct function *fn)
bp_pack_value (&bp, fn->calls_eh_return, 1);
bp_pack_value (&bp, fn->has_force_vectorize_loops, 1);
bp_pack_value (&bp, fn->has_simduid_loops, 1);
+ bp_pack_value (&bp, fn->has_musttail, 1);
bp_pack_value (&bp, fn->assume_function, 1);
bp_pack_value (&bp, fn->va_list_fpr_size, 8);
bp_pack_value (&bp, fn->va_list_gpr_size, 8);
diff --git a/gcc/passes.def b/gcc/passes.def
index 041229e47a68..5b5390e6ac0b 100644
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -444,6 +444,7 @@ 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-cfg.cc b/gcc/tree-cfg.cc
index 7fb7b92966be..e6fd1294b958 100644
--- a/gcc/tree-cfg.cc
+++ b/gcc/tree-cfg.cc
@@ -2290,6 +2290,8 @@ notice_special_calls (gcall *call)
cfun->calls_alloca = true;
if (flags & ECF_RETURNS_TWICE)
cfun->calls_setjmp = true;
+ if (gimple_call_must_tail_p (call))
+ cfun->has_musttail = true;
}
@@ -2301,6 +2303,7 @@ clear_special_calls (void)
{
cfun->calls_alloca = false;
cfun->calls_setjmp = false;
+ cfun->has_musttail = false;
}
/* Remove PHI nodes associated with basic block BB and all edges out of BB. */
diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
index edebb2be245d..59e53558034f 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..0c6df10e64f7 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 +1317,46 @@ 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 *f) final override
+ {
+ if (!f->has_musttail)
+ return 0;
+ 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);
+}
--
2.45.2
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