[PATCH] subreg: Add -fsplit-wide-types-early (PR88233)

[Segher Boessenkool <segher@kernel.crashing.org>]

Currently the second lower-subreg pass is run right before RA.  This
is much too late to be very useful.  At least for targets that do not
have RTL patterns for operations on multi-register modes it is a lot
better to split patterns earlier, before combine and all related
passes.

This adds an option -fsplit-wide-types-early that does that, and
enables it by default for rs6000.


2019-07-07  Segher Boessenkool  <segher@kernel.crashing.org>

	PR rtl-optimization/88233
	* common.opt (fsplit-wide-types-early): New option.
	* common/config/rs6000/rs6000-common.c
	(rs6000_option_optimization_table): Add OPT_fsplit_wide_types_early for
	OPT_LEVELS_ALL.
	* doc/invoke.texi (Optimization Options): Add -fsplit-wide-types-early.
	* lower-subreg.c (pass_lower_subreg2::gate): Add test for
	flag_split_wide_types_early.
	(pass_data_lower_subreg3): New.
	(pass_lower_subreg3): New.
	(make_pass_lower_subreg3): New.
	* passes.def (pass_lower_subreg2): Move after the loop passes.
	(pass_lower_subreg3): New, inserted where pass_lower_subreg2 was.
	* tree-pass.h (make_pass_lower_subreg2): Move up, to its new place in
	the pass pipeline; its previous place is taken by ...
	(make_pass_lower_subreg3): ... this.

---
 gcc/common.opt                           |  4 +++
 gcc/common/config/rs6000/rs6000-common.c |  2 ++
 gcc/doc/invoke.texi                      |  8 +++++-
 gcc/lower-subreg.c                       | 46 +++++++++++++++++++++++++++++++-
 gcc/passes.def                           |  3 ++-
 gcc/tree-pass.h                          |  3 ++-
 6 files changed, 62 insertions(+), 4 deletions(-)

diff --git a/gcc/common.opt b/gcc/common.opt
index 41514df..b998b25 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2430,6 +2430,10 @@ fsplit-wide-types
 Common Report Var(flag_split_wide_types) Optimization
 Split wide types into independent registers.
 
+fsplit-wide-types-early
+Common Report Var(flag_split_wide_types_early) Optimization
+Split wide types into independent registers earlier.
+
 fssa-backprop
 Common Report Var(flag_ssa_backprop) Init(1) Optimization
 Enable backward propagation of use properties at the SSA level.
diff --git a/gcc/common/config/rs6000/rs6000-common.c b/gcc/common/config/rs6000/rs6000-common.c
index 9857b54..4b0c205 100644
--- a/gcc/common/config/rs6000/rs6000-common.c
+++ b/gcc/common/config/rs6000/rs6000-common.c
@@ -31,6 +31,8 @@
 /* Implement TARGET_OPTION_OPTIMIZATION_TABLE.  */
 static const struct default_options rs6000_option_optimization_table[] =
   {
+    /* Split multi-word types early.  */
+    { OPT_LEVELS_ALL, OPT_fsplit_wide_types_early, NULL, 1 },
     /* Enable -fsched-pressure for first pass instruction scheduling.  */
     { OPT_LEVELS_1_PLUS, OPT_fsched_pressure, NULL, 1 },
     { OPT_LEVELS_NONE, 0, NULL, 0 }
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 73d16b5..6349d4c 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -467,7 +467,7 @@ Objective-C and Objective-C++ Dialects}.
 -fsignaling-nans @gol
 -fsingle-precision-constant  -fsplit-ivs-in-unroller  -fsplit-loops@gol
 -fsplit-paths @gol
--fsplit-wide-types  -fssa-backprop  -fssa-phiopt @gol
+-fsplit-wide-types  -fsplit-wide-types-early  -fssa-backprop  -fssa-phiopt @gol
 -fstdarg-opt  -fstore-merging  -fstrict-aliasing @gol
 -fthread-jumps  -ftracer  -ftree-bit-ccp @gol
 -ftree-builtin-call-dce  -ftree-ccp  -ftree-ch @gol
@@ -8731,6 +8731,12 @@ but may make debugging more difficult.
 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
 @option{-Os}.
 
+@item -fsplit-wide-types-early
+@opindex fsplit-wide-types-early
+Fully split wide types early, instead of very late.
+
+This is the default on some targets.
+
 @item -fcse-follow-jumps
 @opindex fcse-follow-jumps
 In common subexpression elimination (CSE), scan through jump instructions
diff --git a/gcc/lower-subreg.c b/gcc/lower-subreg.c
index 4f68a73..e1418e5 100644
--- a/gcc/lower-subreg.c
+++ b/gcc/lower-subreg.c
@@ -1801,7 +1801,8 @@ public:
   {}
 
   /* opt_pass methods: */
-  virtual bool gate (function *) { return flag_split_wide_types != 0; }
+  virtual bool gate (function *) { return flag_split_wide_types
+					  && flag_split_wide_types_early; }
   virtual unsigned int execute (function *)
     {
       decompose_multiword_subregs (true);
@@ -1817,3 +1818,46 @@ make_pass_lower_subreg2 (gcc::context *ctxt)
 {
   return new pass_lower_subreg2 (ctxt);
 }
+
+/* Implement third lower subreg pass.  */
+
+namespace {
+
+const pass_data pass_data_lower_subreg3 =
+{
+  RTL_PASS, /* type */
+  "subreg3", /* name */
+  OPTGROUP_NONE, /* optinfo_flags */
+  TV_LOWER_SUBREG, /* tv_id */
+  0, /* properties_required */
+  0, /* properties_provided */
+  0, /* properties_destroyed */
+  0, /* todo_flags_start */
+  TODO_df_finish, /* todo_flags_finish */
+};
+
+class pass_lower_subreg3 : public rtl_opt_pass
+{
+public:
+  pass_lower_subreg3 (gcc::context *ctxt)
+    : rtl_opt_pass (pass_data_lower_subreg3, ctxt)
+  {}
+
+  /* opt_pass methods: */
+  virtual bool gate (function *) { return flag_split_wide_types
+					  && !flag_split_wide_types_early; }
+  virtual unsigned int execute (function *)
+    {
+      decompose_multiword_subregs (true);
+      return 0;
+    }
+
+}; // class pass_lower_subreg3
+
+} // anon namespace
+
+rtl_opt_pass *
+make_pass_lower_subreg3 (gcc::context *ctxt)
+{
+  return new pass_lower_subreg3 (ctxt);
+}
diff --git a/gcc/passes.def b/gcc/passes.def
index 9a5b0cd..1a7fd14 100644
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -427,6 +427,7 @@ along with GCC; see the file COPYING3.  If not see
 	  NEXT_PASS (pass_rtl_doloop);
 	  NEXT_PASS (pass_rtl_loop_done);
       POP_INSERT_PASSES ()
+      NEXT_PASS (pass_lower_subreg2);
       NEXT_PASS (pass_web);
       NEXT_PASS (pass_rtl_cprop);
       NEXT_PASS (pass_cse2);
@@ -440,7 +441,7 @@ along with GCC; see the file COPYING3.  If not see
       NEXT_PASS (pass_partition_blocks);
       NEXT_PASS (pass_outof_cfg_layout_mode);
       NEXT_PASS (pass_split_all_insns);
-      NEXT_PASS (pass_lower_subreg2);
+      NEXT_PASS (pass_lower_subreg3);
       NEXT_PASS (pass_df_initialize_no_opt);
       NEXT_PASS (pass_stack_ptr_mod);
       NEXT_PASS (pass_mode_switching);
diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
index b27dbdd..7b83293 100644
--- a/gcc/tree-pass.h
+++ b/gcc/tree-pass.h
@@ -552,6 +552,7 @@ extern rtl_opt_pass *make_pass_rtl_unroll_loops (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_rtl_doloop (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_rtl_loop_done (gcc::context *ctxt);
 
+extern rtl_opt_pass *make_pass_lower_subreg2 (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_web (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_cse2 (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_df_initialize_opt (gcc::context *ctxt);
@@ -567,7 +568,7 @@ extern rtl_opt_pass *make_pass_partition_blocks (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_match_asm_constraints (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_split_all_insns (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_fast_rtl_byte_dce (gcc::context *ctxt);
-extern rtl_opt_pass *make_pass_lower_subreg2 (gcc::context *ctxt);
+extern rtl_opt_pass *make_pass_lower_subreg3 (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_mode_switching (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_sms (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_sched (gcc::context *ctxt);
-- 
1.8.3.1