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[PATCH][RFC] Remove RTL loop unswitching
- From: Richard Biener <rguenther at suse dot de>
- To: gcc-patches at gcc dot gnu dot org
- Date: Tue, 15 Apr 2014 11:26:29 +0200 (CEST)
- Subject: [PATCH][RFC] Remove RTL loop unswitching
- Authentication-results: sourceware.org; auth=none
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);