[PATCH][RFC] Remove RTL loop unswitching

[Richard Biener <rguenther at suse dot de>]

This removes RTL loop unswitching (see last years discussion about
compile-time issues of that pass).  RTL loop unswitching is
enabled together with GIMPLE loop unswitching at -O3 and by
-floop-unswitch.  It's clearly the wrong place to do high-level
loop transforms these days, and the cost of maintainance doesn't
outweight the questionable benefit.

Thus the following patch removes it.

Bootstrap / regtest pending on x86_64-unknown-linux-gnu (I hope
for testsuite fallout).

Any objections?

Thanks,
Richard.

2014-04-15  Richard Biener  <rguenther@suse.de>

	* Makefile.in (OBJS): Remove loop-unswitch.o.
	* loop-unswitch.c: Delete.
	* tree-pass.h (make_pass_rtl_unswitch): Remove.
	* passes.def (pass_rtl_unswitch): Likewise.
	* loop-init.c (gate_rtl_unswitch): Likewise.
	(rtl_unswitch): Likewise.
	(pass_data_rtl_unswitch): Likewise.
	(pass_rtl_unswitch): Likewise.
	(make_pass_rtl_unswitch): Likewise.
	* rtl.h (reversed_condition): Likewise.
	(compare_and_jump_seq): Likewise.
	* loop-iv.c (reversed_condition): Move here from loop-unswitch.c
	and make static.
	* loop-unroll.c (compare_and_jump_seq): Likewise.

Index: gcc/Makefile.in
===================================================================
--- gcc/Makefile.in	(revision 209410)
+++ gcc/Makefile.in	(working copy)
@@ -1294,7 +1294,6 @@ OBJS = \
 	loop-invariant.o \
 	loop-iv.o \
 	loop-unroll.o \
-	loop-unswitch.o \
 	lower-subreg.o \
 	lra.o \
 	lra-assigns.o \
Index: gcc/tree-pass.h
===================================================================
--- gcc/tree-pass.h	(revision 209410)
+++ gcc/tree-pass.h	(working copy)
@@ -512,7 +512,6 @@ extern rtl_opt_pass *make_pass_outof_cfg
 extern rtl_opt_pass *make_pass_loop2 (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_rtl_loop_init (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_rtl_move_loop_invariants (gcc::context *ctxt);
-extern rtl_opt_pass *make_pass_rtl_unswitch (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_rtl_unroll_and_peel_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);
Index: gcc/passes.def
===================================================================
--- gcc/passes.def	(revision 209410)
+++ gcc/passes.def	(working copy)
@@ -341,7 +341,6 @@ along with GCC; see the file COPYING3.
       PUSH_INSERT_PASSES_WITHIN (pass_loop2)
 	  NEXT_PASS (pass_rtl_loop_init);
 	  NEXT_PASS (pass_rtl_move_loop_invariants);
-	  NEXT_PASS (pass_rtl_unswitch);
 	  NEXT_PASS (pass_rtl_unroll_and_peel_loops);
 	  NEXT_PASS (pass_rtl_doloop);
 	  NEXT_PASS (pass_rtl_loop_done);
Index: gcc/loop-init.c
===================================================================
--- gcc/loop-init.c	(revision 209410)
+++ gcc/loop-init.c	(working copy)
@@ -518,61 +518,7 @@ make_pass_rtl_move_loop_invariants (gcc:
 }
 
 
-/* Loop unswitching for RTL.  */
-static bool
-gate_rtl_unswitch (void)
-{
-  return flag_unswitch_loops;
-}
-
-static unsigned int
-rtl_unswitch (void)
-{
-  if (number_of_loops (cfun) > 1)
-    unswitch_loops ();
-  return 0;
-}
-
-namespace {
-
-const pass_data pass_data_rtl_unswitch =
-{
-  RTL_PASS, /* type */
-  "loop2_unswitch", /* name */
-  OPTGROUP_LOOP, /* optinfo_flags */
-  true, /* has_gate */
-  true, /* has_execute */
-  TV_LOOP_UNSWITCH, /* tv_id */
-  0, /* properties_required */
-  0, /* properties_provided */
-  0, /* properties_destroyed */
-  0, /* todo_flags_start */
-  TODO_verify_rtl_sharing, /* todo_flags_finish */
-};
-
-class pass_rtl_unswitch : public rtl_opt_pass
-{
-public:
-  pass_rtl_unswitch (gcc::context *ctxt)
-    : rtl_opt_pass (pass_data_rtl_unswitch, ctxt)
-  {}
-
-  /* opt_pass methods: */
-  bool gate () { return gate_rtl_unswitch (); }
-  unsigned int execute () { return rtl_unswitch (); }
-
-}; // class pass_rtl_unswitch
-
-} // anon namespace
-
-rtl_opt_pass *
-make_pass_rtl_unswitch (gcc::context *ctxt)
-{
-  return new pass_rtl_unswitch (ctxt);
-}
-
-
-/* Loop unswitching for RTL.  */
+/* Loop unrolling and peeling for RTL.  */
 static bool
 gate_rtl_unroll_and_peel_loops (void)
 {
Index: gcc/loop-iv.c
===================================================================
--- gcc/loop-iv.c	(revision 209410)
+++ gcc/loop-iv.c	(working copy)
@@ -1732,6 +1732,21 @@ canon_condition (rtx cond)
   return cond;
 }
 
+/* Reverses CONDition; returns NULL if we cannot.  */
+
+static rtx
+reversed_condition (rtx cond)
+{
+  enum rtx_code reversed;
+  reversed = reversed_comparison_code (cond, NULL);
+  if (reversed == UNKNOWN)
+    return NULL_RTX;
+  else
+    return gen_rtx_fmt_ee (reversed,
+			   GET_MODE (cond), XEXP (cond, 0),
+			   XEXP (cond, 1));
+}
+
 /* Tries to use the fact that COND holds to simplify EXPR.  ALTERED is the
    set of altered regs.  */
 
Index: gcc/loop-unroll.c
===================================================================
--- gcc/loop-unroll.c	(revision 209410)
+++ gcc/loop-unroll.c	(working copy)
@@ -1060,6 +1060,59 @@ split_edge_and_insert (edge e, rtx insns
   return bb;
 }
 
+/* Prepare a sequence comparing OP0 with OP1 using COMP and jumping to LABEL if
+   true, with probability PROB.  If CINSN is not NULL, it is the insn to copy
+   in order to create a jump.  */
+
+static rtx
+compare_and_jump_seq (rtx op0, rtx op1, enum rtx_code comp, rtx label, int prob,
+		      rtx cinsn)
+{
+  rtx seq, jump, cond;
+  enum machine_mode mode;
+
+  mode = GET_MODE (op0);
+  if (mode == VOIDmode)
+    mode = GET_MODE (op1);
+
+  start_sequence ();
+  if (GET_MODE_CLASS (mode) == MODE_CC)
+    {
+      /* A hack -- there seems to be no easy generic way how to make a
+	 conditional jump from a ccmode comparison.  */
+      gcc_assert (cinsn);
+      cond = XEXP (SET_SRC (pc_set (cinsn)), 0);
+      gcc_assert (GET_CODE (cond) == comp);
+      gcc_assert (rtx_equal_p (op0, XEXP (cond, 0)));
+      gcc_assert (rtx_equal_p (op1, XEXP (cond, 1)));
+      emit_jump_insn (copy_insn (PATTERN (cinsn)));
+      jump = get_last_insn ();
+      gcc_assert (JUMP_P (jump));
+      JUMP_LABEL (jump) = JUMP_LABEL (cinsn);
+      LABEL_NUSES (JUMP_LABEL (jump))++;
+      redirect_jump (jump, label, 0);
+    }
+  else
+    {
+      gcc_assert (!cinsn);
+
+      op0 = force_operand (op0, NULL_RTX);
+      op1 = force_operand (op1, NULL_RTX);
+      do_compare_rtx_and_jump (op0, op1, comp, 0,
+			       mode, NULL_RTX, NULL_RTX, label, -1);
+      jump = get_last_insn ();
+      gcc_assert (JUMP_P (jump));
+      JUMP_LABEL (jump) = label;
+      LABEL_NUSES (label)++;
+    }
+  add_int_reg_note (jump, REG_BR_PROB, prob);
+
+  seq = get_insns ();
+  end_sequence ();
+
+  return seq;
+}
+
 /* Unroll LOOP for which we are able to count number of iterations in runtime
    LOOP->LPT_DECISION.TIMES times.  The transformation does this (with some
    extra care for case n < 0):
Index: gcc/rtl.h
===================================================================
--- gcc/rtl.h	(revision 209410)
+++ gcc/rtl.h	(working copy)
@@ -2743,10 +2743,6 @@ extern unsigned int variable_tracking_ma
 extern void get_mode_bounds (enum machine_mode, int, enum machine_mode,
 			     rtx *, rtx *);
 
-/* In loop-unswitch.c  */
-extern rtx reversed_condition (rtx);
-extern rtx compare_and_jump_seq (rtx, rtx, enum rtx_code, rtx, int, rtx);
-
 /* In loop-iv.c  */
 extern rtx canon_condition (rtx);
 extern void simplify_using_condition (rtx, rtx *, bitmap);