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Re: Gimple loop splitting v2
- From: Andrew Pinski <pinskia at gmail dot com>
- To: Michael Matz <matz at suse dot de>
- Cc: Jeff Law <law at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 25 Jul 2016 13:57:30 -0700
- Subject: Re: Gimple loop splitting v2
- Authentication-results: sourceware.org; auth=none
- References: <alpine.LSU.2.20.1511121734040.11029@wotan.suse.de> <5645083A.5070607@redhat.com> <alpine.LSU.2.20.1511161453390.11029@wotan.suse.de> <564A6648.6000002@redhat.com> <alpine.LSU.2.20.1512011711210.13533@wotan.suse.de> <565E25E7.7050202@redhat.com> <alpine.LSU.2.20.1512021420420.13533@wotan.suse.de>
On Wed, Dec 2, 2015 at 5:23 AM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Tue, 1 Dec 2015, Jeff Law wrote:
>
>> > So, okay for trunk?
>> -ENOPATCH
>
> Sigh :)
> Here it is.
I found one problem with it.
Take:
void f(int *a, int M, int *b)
{
for(int i = 0; i <= M; i++)
{
if (i < M)
a[i] = i;
}
}
---- CUT ---
There are two issues with the code as below. The outer most loop's
aux is still set which causes the vectorizer not to vector the loop.
The other issue is I need to run pass_scev_cprop after pass_loop_split
to get the induction variable usage after the loop gone so the
vectorizer will work.
Something like (note this is copy and paste from a terminal):
diff --git a/gcc/passes.def b/gcc/passes.def
index c327900..e8d6ea6 100644
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -262,8 +262,8 @@ along with GCC; see the file COPYING3. If not see
NEXT_PASS (pass_copy_prop);
NEXT_PASS (pass_dce);
NEXT_PASS (pass_tree_unswitch);
- NEXT_PASS (pass_scev_cprop);
NEXT_PASS (pass_loop_split);
+ NEXT_PASS (pass_scev_cprop);
NEXT_PASS (pass_record_bounds);
NEXT_PASS (pass_loop_distribution);
NEXT_PASS (pass_copy_prop);
diff --git a/gcc/tree-ssa-loop-split.c b/gcc/tree-ssa-loop-split.c
index 5411530..e72ef19 100644
--- a/gcc/tree-ssa-loop-split.c
+++ b/gcc/tree-ssa-loop-split.c
@@ -592,7 +592,11 @@ tree_ssa_split_loops (void)
gcc_assert (scev_initialized_p ());
FOR_EACH_LOOP (loop, 0)
- loop->aux = NULL;
+ {
+ loop->aux = NULL;
+ if (loop_outer (loop))
+ loop_outer (loop)->aux = NULL;
+ }
/* Go through all loops starting from innermost. */
FOR_EACH_LOOP (loop, LI_FROM_INNERMOST)
@@ -631,7 +635,11 @@ tree_ssa_split_loops (void)
}
FOR_EACH_LOOP (loop, 0)
- loop->aux = NULL;
+ {
+ loop->aux = NULL;
+ if (loop_outer (loop))
+ loop_outer (loop)->aux = NULL;
+ }
if (changed)
return TODO_cleanup_cfg;
----- CUT -----
Thanks,
Andrew
>
>
> Ciao,
> Michael.
> * common.opt (-fsplit-loops): New flag.
> * passes.def (pass_loop_split): Add.
> * opts.c (default_options_table): Add OPT_fsplit_loops entry at -O3.
> (enable_fdo_optimizations): Add loop splitting.
> * timevar.def (TV_LOOP_SPLIT): Add.
> * tree-pass.h (make_pass_loop_split): Declare.
> * tree-ssa-loop-manip.h (rewrite_into_loop_closed_ssa_1): Declare.
> * tree-ssa-loop-unswitch.c: Include tree-ssa-loop-manip.h,
> * tree-ssa-loop-split.c: New file.
> * Makefile.in (OBJS): Add tree-ssa-loop-split.o.
> * doc/invoke.texi (fsplit-loops): Document.
> * doc/passes.texi (Loop optimization): Add paragraph about loop
> splitting.
>
> testsuite/
> * gcc.dg/loop-split.c: New test.
>
> Index: common.opt
> ===================================================================
> --- common.opt (revision 231115)
> +++ common.opt (working copy)
> @@ -2453,6 +2457,10 @@ funswitch-loops
> Common Report Var(flag_unswitch_loops) Optimization
> Perform loop unswitching.
>
> +fsplit-loops
> +Common Report Var(flag_split_loops) Optimization
> +Perform loop splitting.
> +
> funwind-tables
> Common Report Var(flag_unwind_tables) Optimization
> Just generate unwind tables for exception handling.
> Index: passes.def
> ===================================================================
> --- passes.def (revision 231115)
> +++ passes.def (working copy)
> @@ -252,6 +252,7 @@ along with GCC; see the file COPYING3.
> NEXT_PASS (pass_dce);
> NEXT_PASS (pass_tree_unswitch);
> NEXT_PASS (pass_scev_cprop);
> + NEXT_PASS (pass_loop_split);
> NEXT_PASS (pass_record_bounds);
> NEXT_PASS (pass_loop_distribution);
> NEXT_PASS (pass_copy_prop);
> Index: opts.c
> ===================================================================
> --- opts.c (revision 231115)
> +++ opts.c (working copy)
> @@ -532,6 +532,7 @@ static const struct default_options defa
> regardless of them being declared inline. */
> { OPT_LEVELS_3_PLUS_AND_SIZE, OPT_finline_functions, NULL, 1 },
> { OPT_LEVELS_1_PLUS_NOT_DEBUG, OPT_finline_functions_called_once, NULL, 1 },
> + { OPT_LEVELS_3_PLUS, OPT_fsplit_loops, NULL, 1 },
> { OPT_LEVELS_3_PLUS, OPT_funswitch_loops, NULL, 1 },
> { OPT_LEVELS_3_PLUS, OPT_fgcse_after_reload, NULL, 1 },
> { OPT_LEVELS_3_PLUS, OPT_ftree_loop_vectorize, NULL, 1 },
> @@ -1411,6 +1412,8 @@ enable_fdo_optimizations (struct gcc_opt
> opts->x_flag_ipa_cp_alignment = value;
> if (!opts_set->x_flag_predictive_commoning)
> opts->x_flag_predictive_commoning = value;
> + if (!opts_set->x_flag_split_loops)
> + opts->x_flag_split_loops = value;
> if (!opts_set->x_flag_unswitch_loops)
> opts->x_flag_unswitch_loops = value;
> if (!opts_set->x_flag_gcse_after_reload)
> Index: timevar.def
> ===================================================================
> --- timevar.def (revision 231115)
> +++ timevar.def (working copy)
> @@ -182,6 +182,7 @@ DEFTIMEVAR (TV_LIM , "
> DEFTIMEVAR (TV_TREE_LOOP_IVCANON , "tree canonical iv")
> DEFTIMEVAR (TV_SCEV_CONST , "scev constant prop")
> DEFTIMEVAR (TV_TREE_LOOP_UNSWITCH , "tree loop unswitching")
> +DEFTIMEVAR (TV_LOOP_SPLIT , "loop splitting")
> DEFTIMEVAR (TV_COMPLETE_UNROLL , "complete unrolling")
> DEFTIMEVAR (TV_TREE_PARALLELIZE_LOOPS, "tree parallelize loops")
> DEFTIMEVAR (TV_TREE_VECTORIZATION , "tree vectorization")
> Index: tree-pass.h
> ===================================================================
> --- tree-pass.h (revision 231115)
> +++ tree-pass.h (working copy)
> @@ -370,6 +370,7 @@ extern gimple_opt_pass *make_pass_tree_n
> extern gimple_opt_pass *make_pass_tree_loop_init (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_lim (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_tree_unswitch (gcc::context *ctxt);
> +extern gimple_opt_pass *make_pass_loop_split (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_predcom (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_iv_canon (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_scev_cprop (gcc::context *ctxt);
> Index: tree-ssa-loop-manip.h
> ===================================================================
> --- tree-ssa-loop-manip.h (revision 231115)
> +++ tree-ssa-loop-manip.h (working copy)
> @@ -24,6 +24,8 @@ typedef void (*transform_callback)(struc
>
> extern void create_iv (tree, tree, tree, struct loop *, gimple_stmt_iterator *,
> bool, tree *, tree *);
> +extern void rewrite_into_loop_closed_ssa_1 (bitmap, unsigned, int,
> + struct loop *);
> extern void rewrite_into_loop_closed_ssa (bitmap, unsigned);
> extern void rewrite_virtuals_into_loop_closed_ssa (struct loop *);
> extern void verify_loop_closed_ssa (bool);
> Index: Makefile.in
> ===================================================================
> --- Makefile.in (revision 231115)
> +++ Makefile.in (working copy)
> @@ -1474,6 +1474,7 @@ OBJS = \
> tree-ssa-loop-manip.o \
> tree-ssa-loop-niter.o \
> tree-ssa-loop-prefetch.o \
> + tree-ssa-loop-split.o \
> tree-ssa-loop-unswitch.o \
> tree-ssa-loop.o \
> tree-ssa-math-opts.o \
> Index: tree-ssa-loop-split.c
> ===================================================================
> --- tree-ssa-loop-split.c (revision 0)
> +++ tree-ssa-loop-split.c (working copy)
> @@ -0,0 +1,686 @@
> +/* Loop splitting.
> + Copyright (C) 2015 Free Software Foundation, Inc.
> +
> +This file is part of GCC.
> +
> +GCC is free software; you can redistribute it and/or modify it
> +under the terms of the GNU General Public License as published by the
> +Free Software Foundation; either version 3, or (at your option) any
> +later version.
> +
> +GCC is distributed in the hope that it will be useful, but WITHOUT
> +ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> +FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
> +for more details.
> +
> +You should have received a copy of the GNU General Public License
> +along with GCC; see the file COPYING3. If not see
> +<http://www.gnu.org/licenses/>. */
> +
> +#include "config.h"
> +#include "system.h"
> +#include "coretypes.h"
> +#include "backend.h"
> +#include "tree.h"
> +#include "gimple.h"
> +#include "tree-pass.h"
> +#include "ssa.h"
> +#include "fold-const.h"
> +#include "tree-cfg.h"
> +#include "tree-ssa.h"
> +#include "tree-ssa-loop-niter.h"
> +#include "tree-ssa-loop.h"
> +#include "tree-ssa-loop-manip.h"
> +#include "tree-into-ssa.h"
> +#include "cfgloop.h"
> +#include "tree-scalar-evolution.h"
> +#include "gimple-iterator.h"
> +#include "gimple-pretty-print.h"
> +#include "cfghooks.h"
> +#include "gimple-fold.h"
> +#include "gimplify-me.h"
> +
> +/* This file implements loop splitting, i.e. transformation of loops like
> +
> + for (i = 0; i < 100; i++)
> + {
> + if (i < 50)
> + A;
> + else
> + B;
> + }
> +
> + into:
> +
> + for (i = 0; i < 50; i++)
> + {
> + A;
> + }
> + for (; i < 100; i++)
> + {
> + B;
> + }
> +
> + */
> +
> +/* Return true when BB inside LOOP is a potential iteration space
> + split point, i.e. ends with a condition like "IV < comp", which
> + is true on one side of the iteration space and false on the other,
> + and the split point can be computed. If so, also return the border
> + point in *BORDER and the comparison induction variable in IV. */
> +
> +static tree
> +split_at_bb_p (struct loop *loop, basic_block bb, tree *border, affine_iv *iv)
> +{
> + gimple *last;
> + gcond *stmt;
> + affine_iv iv2;
> +
> + /* BB must end in a simple conditional jump. */
> + last = last_stmt (bb);
> + if (!last || gimple_code (last) != GIMPLE_COND)
> + return NULL_TREE;
> + stmt = as_a <gcond *> (last);
> +
> + enum tree_code code = gimple_cond_code (stmt);
> +
> + /* Only handle relational comparisons, for equality and non-equality
> + we'd have to split the loop into two loops and a middle statement. */
> + switch (code)
> + {
> + case LT_EXPR:
> + case LE_EXPR:
> + case GT_EXPR:
> + case GE_EXPR:
> + break;
> + default:
> + return NULL_TREE;
> + }
> +
> + if (loop_exits_from_bb_p (loop, bb))
> + return NULL_TREE;
> +
> + tree op0 = gimple_cond_lhs (stmt);
> + tree op1 = gimple_cond_rhs (stmt);
> +
> + if (!simple_iv (loop, loop, op0, iv, false))
> + return NULL_TREE;
> + if (!simple_iv (loop, loop, op1, &iv2, false))
> + return NULL_TREE;
> +
> + /* Make it so, that the first argument of the condition is
> + the looping one (only swap. */
> + if (!integer_zerop (iv2.step))
> + {
> + std::swap (op0, op1);
> + std::swap (*iv, iv2);
> + code = swap_tree_comparison (code);
> + gimple_cond_set_condition (stmt, code, op0, op1);
> + update_stmt (stmt);
> + }
> + else if (integer_zerop (iv->step))
> + return NULL_TREE;
> + if (!integer_zerop (iv2.step))
> + return NULL_TREE;
> +
> + if (dump_file && (dump_flags & TDF_DETAILS))
> + {
> + fprintf (dump_file, "Found potential split point: ");
> + print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
> + fprintf (dump_file, " { ");
> + print_generic_expr (dump_file, iv->base, TDF_SLIM);
> + fprintf (dump_file, " + I*");
> + print_generic_expr (dump_file, iv->step, TDF_SLIM);
> + fprintf (dump_file, " } %s ", get_tree_code_name (code));
> + print_generic_expr (dump_file, iv2.base, TDF_SLIM);
> + fprintf (dump_file, "\n");
> + }
> +
> + *border = iv2.base;
> + return op0;
> +}
> +
> +/* Given a GUARD conditional stmt inside LOOP, which we want to make always
> + true or false depending on INITIAL_TRUE, and adjusted values NEXTVAL
> + (a post-increment IV) and NEWBOUND (the comparator) adjust the loop
> + exit test statement to loop back only if the GUARD statement will
> + also be true/false in the next iteration. */
> +
> +static void
> +patch_loop_exit (struct loop *loop, gcond *guard, tree nextval, tree newbound,
> + bool initial_true)
> +{
> + edge exit = single_exit (loop);
> + gcond *stmt = as_a <gcond *> (last_stmt (exit->src));
> + gimple_cond_set_condition (stmt, gimple_cond_code (guard),
> + nextval, newbound);
> + update_stmt (stmt);
> +
> + edge stay = single_pred_edge (loop->latch);
> +
> + exit->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
> + stay->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
> +
> + if (initial_true)
> + {
> + exit->flags |= EDGE_FALSE_VALUE;
> + stay->flags |= EDGE_TRUE_VALUE;
> + }
> + else
> + {
> + exit->flags |= EDGE_TRUE_VALUE;
> + stay->flags |= EDGE_FALSE_VALUE;
> + }
> +}
> +
> +/* Give an induction variable GUARD_IV, and its affine descriptor IV,
> + find the loop phi node in LOOP defining it directly, or create
> + such phi node. Return that phi node. */
> +
> +static gphi *
> +find_or_create_guard_phi (struct loop *loop, tree guard_iv, affine_iv * /*iv*/)
> +{
> + gimple *def = SSA_NAME_DEF_STMT (guard_iv);
> + gphi *phi;
> + if ((phi = dyn_cast <gphi *> (def))
> + && gimple_bb (phi) == loop->header)
> + return phi;
> +
> + /* XXX Create the PHI instead. */
> + return NULL;
> +}
> +
> +/* This function updates the SSA form after connect_loops made a new
> + edge NEW_E leading from LOOP1 exit to LOOP2 (via in intermediate
> + conditional). I.e. the second loop can now be entered either
> + via the original entry or via NEW_E, so the entry values of LOOP2
> + phi nodes are either the original ones or those at the exit
> + of LOOP1. Insert new phi nodes in LOOP2 pre-header reflecting
> + this. */
> +
> +static void
> +connect_loop_phis (struct loop *loop1, struct loop *loop2, edge new_e)
> +{
> + basic_block rest = loop_preheader_edge (loop2)->src;
> + gcc_assert (new_e->dest == rest);
> + edge skip_first = EDGE_PRED (rest, EDGE_PRED (rest, 0) == new_e);
> +
> + edge firste = loop_preheader_edge (loop1);
> + edge seconde = loop_preheader_edge (loop2);
> + edge firstn = loop_latch_edge (loop1);
> + gphi_iterator psi_first, psi_second;
> + for (psi_first = gsi_start_phis (loop1->header),
> + psi_second = gsi_start_phis (loop2->header);
> + !gsi_end_p (psi_first);
> + gsi_next (&psi_first), gsi_next (&psi_second))
> + {
> + tree init, next, new_init;
> + use_operand_p op;
> + gphi *phi_first = psi_first.phi ();
> + gphi *phi_second = psi_second.phi ();
> +
> + init = PHI_ARG_DEF_FROM_EDGE (phi_first, firste);
> + next = PHI_ARG_DEF_FROM_EDGE (phi_first, firstn);
> + op = PHI_ARG_DEF_PTR_FROM_EDGE (phi_second, seconde);
> + gcc_assert (operand_equal_for_phi_arg_p (init, USE_FROM_PTR (op)));
> +
> + /* Prefer using original variable as a base for the new ssa name.
> + This is necessary for virtual ops, and useful in order to avoid
> + losing debug info for real ops. */
> + if (TREE_CODE (next) == SSA_NAME
> + && useless_type_conversion_p (TREE_TYPE (next),
> + TREE_TYPE (init)))
> + new_init = copy_ssa_name (next);
> + else if (TREE_CODE (init) == SSA_NAME
> + && useless_type_conversion_p (TREE_TYPE (init),
> + TREE_TYPE (next)))
> + new_init = copy_ssa_name (init);
> + else if (useless_type_conversion_p (TREE_TYPE (next),
> + TREE_TYPE (init)))
> + new_init = make_temp_ssa_name (TREE_TYPE (next), NULL,
> + "unrinittmp");
> + else
> + new_init = make_temp_ssa_name (TREE_TYPE (init), NULL,
> + "unrinittmp");
> +
> + gphi * newphi = create_phi_node (new_init, rest);
> + add_phi_arg (newphi, init, skip_first, UNKNOWN_LOCATION);
> + add_phi_arg (newphi, next, new_e, UNKNOWN_LOCATION);
> + SET_USE (op, new_init);
> + }
> +}
> +
> +/* The two loops LOOP1 and LOOP2 were just created by loop versioning,
> + they are still equivalent and placed in two arms of a diamond, like so:
> +
> + .------if (cond)------.
> + v v
> + pre1 pre2
> + | |
> + .--->h1 h2<----.
> + | | | |
> + | ex1---. .---ex2 |
> + | / | | \ |
> + '---l1 X | l2---'
> + | |
> + | |
> + '--->join<---'
> +
> + This function transforms the program such that LOOP1 is conditionally
> + falling through to LOOP2, or skipping it. This is done by splitting
> + the ex1->join edge at X in the diagram above, and inserting a condition
> + whose one arm goes to pre2, resulting in this situation:
> +
> + .------if (cond)------.
> + v v
> + pre1 .---------->pre2
> + | | |
> + .--->h1 | h2<----.
> + | | | | |
> + | ex1---. | .---ex2 |
> + | / v | | \ |
> + '---l1 skip---' | l2---'
> + | |
> + | |
> + '--->join<---'
> +
> +
> + The condition used is the exit condition of LOOP1, which effectively means
> + that when the first loop exits (for whatever reason) but the real original
> + exit expression is still false the second loop will be entered.
> + The function returns the new edge cond->pre2.
> +
> + This doesn't update the SSA form, see connect_loop_phis for that. */
> +
> +static edge
> +connect_loops (struct loop *loop1, struct loop *loop2)
> +{
> + edge exit = single_exit (loop1);
> + basic_block skip_bb = split_edge (exit);
> + gcond *skip_stmt;
> + gimple_stmt_iterator gsi;
> + edge new_e, skip_e;
> +
> + gimple *stmt = last_stmt (exit->src);
> + skip_stmt = gimple_build_cond (gimple_cond_code (stmt),
> + gimple_cond_lhs (stmt),
> + gimple_cond_rhs (stmt),
> + NULL_TREE, NULL_TREE);
> + gsi = gsi_last_bb (skip_bb);
> + gsi_insert_after (&gsi, skip_stmt, GSI_NEW_STMT);
> +
> + skip_e = EDGE_SUCC (skip_bb, 0);
> + skip_e->flags &= ~EDGE_FALLTHRU;
> + new_e = make_edge (skip_bb, loop_preheader_edge (loop2)->src, 0);
> + if (exit->flags & EDGE_TRUE_VALUE)
> + {
> + skip_e->flags |= EDGE_TRUE_VALUE;
> + new_e->flags |= EDGE_FALSE_VALUE;
> + }
> + else
> + {
> + skip_e->flags |= EDGE_FALSE_VALUE;
> + new_e->flags |= EDGE_TRUE_VALUE;
> + }
> +
> + new_e->count = skip_bb->count;
> + new_e->probability = PROB_LIKELY;
> + new_e->count = apply_probability (skip_e->count, PROB_LIKELY);
> + skip_e->count -= new_e->count;
> + skip_e->probability = inverse_probability (PROB_LIKELY);
> +
> + return new_e;
> +}
> +
> +/* This returns the new bound for iterations given the original iteration
> + space in NITER, an arbitrary new bound BORDER, assumed to be some
> + comparison value with a different IV, the initial value GUARD_INIT of
> + that other IV, and the comparison code GUARD_CODE that compares
> + that other IV with BORDER. We return an SSA name, and place any
> + necessary statements for that computation into *STMTS.
> +
> + For example for such a loop:
> +
> + for (i = beg, j = guard_init; i < end; i++, j++)
> + if (j < border) // this is supposed to be true/false
> + ...
> +
> + we want to return a new bound (on j) that makes the loop iterate
> + as long as the condition j < border stays true. We also don't want
> + to iterate more often than the original loop, so we have to introduce
> + some cut-off as well (via min/max), effectively resulting in:
> +
> + newend = min (end+guard_init-beg, border)
> + for (i = beg; j = guard_init; j < newend; i++, j++)
> + if (j < c)
> + ...
> +
> + Depending on the direction of the IVs and if the exit tests
> + are strict or non-strict we need to use MIN or MAX,
> + and add or subtract 1. This routine computes newend above. */
> +
> +static tree
> +compute_new_first_bound (gimple_seq *stmts, struct tree_niter_desc *niter,
> + tree border,
> + enum tree_code guard_code, tree guard_init)
> +{
> + /* The niter structure contains the after-increment IV, we need
> + the loop-enter base, so subtract STEP once. */
> + tree controlbase = force_gimple_operand (niter->control.base,
> + stmts, true, NULL_TREE);
> + tree controlstep = niter->control.step;
> + tree enddiff;
> + if (POINTER_TYPE_P (TREE_TYPE (controlbase)))
> + {
> + controlstep = gimple_build (stmts, NEGATE_EXPR,
> + TREE_TYPE (controlstep), controlstep);
> + enddiff = gimple_build (stmts, POINTER_PLUS_EXPR,
> + TREE_TYPE (controlbase),
> + controlbase, controlstep);
> + }
> + else
> + enddiff = gimple_build (stmts, MINUS_EXPR,
> + TREE_TYPE (controlbase),
> + controlbase, controlstep);
> +
> + /* Compute beg-guard_init. */
> + if (POINTER_TYPE_P (TREE_TYPE (enddiff)))
> + {
> + tree tem = gimple_convert (stmts, sizetype, guard_init);
> + tem = gimple_build (stmts, NEGATE_EXPR, sizetype, tem);
> + enddiff = gimple_build (stmts, POINTER_PLUS_EXPR,
> + TREE_TYPE (enddiff),
> + enddiff, tem);
> + }
> + else
> + enddiff = gimple_build (stmts, MINUS_EXPR, TREE_TYPE (enddiff),
> + enddiff, guard_init);
> +
> + /* Compute end-(beg-guard_init). */
> + gimple_seq stmts2;
> + tree newbound = force_gimple_operand (niter->bound, &stmts2,
> + true, NULL_TREE);
> + gimple_seq_add_seq_without_update (stmts, stmts2);
> +
> + if (POINTER_TYPE_P (TREE_TYPE (enddiff))
> + || POINTER_TYPE_P (TREE_TYPE (newbound)))
> + {
> + enddiff = gimple_convert (stmts, sizetype, enddiff);
> + enddiff = gimple_build (stmts, NEGATE_EXPR, sizetype, enddiff);
> + newbound = gimple_build (stmts, POINTER_PLUS_EXPR,
> + TREE_TYPE (newbound),
> + newbound, enddiff);
> + }
> + else
> + newbound = gimple_build (stmts, MINUS_EXPR, TREE_TYPE (enddiff),
> + newbound, enddiff);
> +
> + /* Depending on the direction of the IVs the new bound for the first
> + loop is the minimum or maximum of old bound and border.
> + Also, if the guard condition isn't strictly less or greater,
> + we need to adjust the bound. */
> + int addbound = 0;
> + enum tree_code minmax;
> + if (niter->cmp == LT_EXPR)
> + {
> + /* GT and LE are the same, inverted. */
> + if (guard_code == GT_EXPR || guard_code == LE_EXPR)
> + addbound = -1;
> + minmax = MIN_EXPR;
> + }
> + else
> + {
> + gcc_assert (niter->cmp == GT_EXPR);
> + if (guard_code == GE_EXPR || guard_code == LT_EXPR)
> + addbound = 1;
> + minmax = MAX_EXPR;
> + }
> +
> + if (addbound)
> + {
> + tree type2 = TREE_TYPE (newbound);
> + if (POINTER_TYPE_P (type2))
> + type2 = sizetype;
> + newbound = gimple_build (stmts,
> + POINTER_TYPE_P (TREE_TYPE (newbound))
> + ? POINTER_PLUS_EXPR : PLUS_EXPR,
> + TREE_TYPE (newbound),
> + newbound,
> + build_int_cst (type2, addbound));
> + }
> +
> + tree newend = gimple_build (stmts, minmax, TREE_TYPE (border),
> + border, newbound);
> + return newend;
> +}
> +
> +/* Checks if LOOP contains an conditional block whose condition
> + depends on which side in the iteration space it is, and if so
> + splits the iteration space into two loops. Returns true if the
> + loop was split. NITER must contain the iteration descriptor for the
> + single exit of LOOP. */
> +
> +static bool
> +split_loop (struct loop *loop1, struct tree_niter_desc *niter)
> +{
> + basic_block *bbs;
> + unsigned i;
> + bool changed = false;
> + tree guard_iv;
> + tree border;
> + affine_iv iv;
> +
> + bbs = get_loop_body (loop1);
> +
> + /* Find a splitting opportunity. */
> + for (i = 0; i < loop1->num_nodes; i++)
> + if ((guard_iv = split_at_bb_p (loop1, bbs[i], &border, &iv)))
> + {
> + /* Handling opposite steps is not implemented yet. Neither
> + is handling different step sizes. */
> + if ((tree_int_cst_sign_bit (iv.step)
> + != tree_int_cst_sign_bit (niter->control.step))
> + || !tree_int_cst_equal (iv.step, niter->control.step))
> + continue;
> +
> + /* Find a loop PHI node that defines guard_iv directly,
> + or create one doing that. */
> + gphi *phi = find_or_create_guard_phi (loop1, guard_iv, &iv);
> + if (!phi)
> + continue;
> + gcond *guard_stmt = as_a<gcond *> (last_stmt (bbs[i]));
> + tree guard_init = PHI_ARG_DEF_FROM_EDGE (phi,
> + loop_preheader_edge (loop1));
> + enum tree_code guard_code = gimple_cond_code (guard_stmt);
> +
> + /* Loop splitting is implemented by versioning the loop, placing
> + the new loop after the old loop, make the first loop iterate
> + as long as the conditional stays true (or false) and let the
> + second (new) loop handle the rest of the iterations.
> +
> + First we need to determine if the condition will start being true
> + or false in the first loop. */
> + bool initial_true;
> + switch (guard_code)
> + {
> + case LT_EXPR:
> + case LE_EXPR:
> + initial_true = !tree_int_cst_sign_bit (iv.step);
> + break;
> + case GT_EXPR:
> + case GE_EXPR:
> + initial_true = tree_int_cst_sign_bit (iv.step);
> + break;
> + default:
> + gcc_unreachable ();
> + }
> +
> + /* Build a condition that will skip the first loop when the
> + guard condition won't ever be true (or false). */
> + gimple_seq stmts2;
> + border = force_gimple_operand (border, &stmts2, true, NULL_TREE);
> + if (stmts2)
> + gsi_insert_seq_on_edge_immediate (loop_preheader_edge (loop1),
> + stmts2);
> + tree cond = build2 (guard_code, boolean_type_node, guard_init, border);
> + if (!initial_true)
> + cond = fold_build1 (TRUTH_NOT_EXPR, boolean_type_node, cond);
> +
> + /* Now version the loop, placing loop2 after loop1 connecting
> + them, and fix up SSA form for that. */
> + initialize_original_copy_tables ();
> + basic_block cond_bb;
> + struct loop *loop2 = loop_version (loop1, cond, &cond_bb,
> + REG_BR_PROB_BASE, REG_BR_PROB_BASE,
> + REG_BR_PROB_BASE, true);
> + gcc_assert (loop2);
> + update_ssa (TODO_update_ssa);
> +
> + edge new_e = connect_loops (loop1, loop2);
> + connect_loop_phis (loop1, loop2, new_e);
> +
> + /* The iterations of the second loop is now already
> + exactly those that the first loop didn't do, but the
> + iteration space of the first loop is still the original one.
> + Compute the new bound for the guarding IV and patch the
> + loop exit to use it instead of original IV and bound. */
> + gimple_seq stmts = NULL;
> + tree newend = compute_new_first_bound (&stmts, niter, border,
> + guard_code, guard_init);
> + if (stmts)
> + gsi_insert_seq_on_edge_immediate (loop_preheader_edge (loop1),
> + stmts);
> + tree guard_next = PHI_ARG_DEF_FROM_EDGE (phi, loop_latch_edge (loop1));
> + patch_loop_exit (loop1, guard_stmt, guard_next, newend, initial_true);
> +
> + /* Finally patch out the two copies of the condition to be always
> + true/false (or opposite). */
> + gcond *force_true = as_a<gcond *> (last_stmt (bbs[i]));
> + gcond *force_false = as_a<gcond *> (last_stmt (get_bb_copy (bbs[i])));
> + if (!initial_true)
> + std::swap (force_true, force_false);
> + gimple_cond_make_true (force_true);
> + gimple_cond_make_false (force_false);
> + update_stmt (force_true);
> + update_stmt (force_false);
> +
> + free_original_copy_tables ();
> +
> + /* We destroyed LCSSA form above. Eventually we might be able
> + to fix it on the fly, for now simply punt and use the helper. */
> + rewrite_into_loop_closed_ssa_1 (NULL, 0, SSA_OP_USE, loop1);
> +
> + changed = true;
> + if (dump_file && (dump_flags & TDF_DETAILS))
> + fprintf (dump_file, ";; Loop split.\n");
> +
> + /* Only deal with the first opportunity. */
> + break;
> + }
> +
> + free (bbs);
> + return changed;
> +}
> +
> +/* Main entry point. Perform loop splitting on all suitable loops. */
> +
> +static unsigned int
> +tree_ssa_split_loops (void)
> +{
> + struct loop *loop;
> + bool changed = false;
> +
> + gcc_assert (scev_initialized_p ());
> + FOR_EACH_LOOP (loop, 0)
> + loop->aux = NULL;
> +
> + /* Go through all loops starting from innermost. */
> + FOR_EACH_LOOP (loop, LI_FROM_INNERMOST)
> + {
> + struct tree_niter_desc niter;
> + if (loop->aux)
> + {
> + /* If any of our inner loops was split, don't split us,
> + and mark our containing loop as having had splits as well. */
> + loop_outer (loop)->aux = loop;
> + continue;
> + }
> +
> + if (single_exit (loop)
> + /* ??? We could handle non-empty latches when we split
> + the latch edge (not the exit edge), and put the new
> + exit condition in the new block. OTOH this executes some
> + code unconditionally that might have been skipped by the
> + original exit before. */
> + && empty_block_p (loop->latch)
> + && !optimize_loop_for_size_p (loop)
> + && number_of_iterations_exit (loop, single_exit (loop), &niter,
> + false, true)
> + && niter.cmp != ERROR_MARK
> + /* We can't yet handle loops controlled by a != predicate. */
> + && niter.cmp != NE_EXPR)
> + {
> + if (split_loop (loop, &niter))
> + {
> + /* Mark our containing loop as having had some split inner
> + loops. */
> + loop_outer (loop)->aux = loop;
> + changed = true;
> + }
> + }
> + }
> +
> + FOR_EACH_LOOP (loop, 0)
> + loop->aux = NULL;
> +
> + if (changed)
> + return TODO_cleanup_cfg;
> + return 0;
> +}
> +
> +/* Loop splitting pass. */
> +
> +namespace {
> +
> +const pass_data pass_data_loop_split =
> +{
> + GIMPLE_PASS, /* type */
> + "lsplit", /* name */
> + OPTGROUP_LOOP, /* optinfo_flags */
> + TV_LOOP_SPLIT, /* tv_id */
> + PROP_cfg, /* properties_required */
> + 0, /* properties_provided */
> + 0, /* properties_destroyed */
> + 0, /* todo_flags_start */
> + 0, /* todo_flags_finish */
> +};
> +
> +class pass_loop_split : public gimple_opt_pass
> +{
> +public:
> + pass_loop_split (gcc::context *ctxt)
> + : gimple_opt_pass (pass_data_loop_split, ctxt)
> + {}
> +
> + /* opt_pass methods: */
> + virtual bool gate (function *) { return flag_split_loops != 0; }
> + virtual unsigned int execute (function *);
> +
> +}; // class pass_loop_split
> +
> +unsigned int
> +pass_loop_split::execute (function *fun)
> +{
> + if (number_of_loops (fun) <= 1)
> + return 0;
> +
> + return tree_ssa_split_loops ();
> +}
> +
> +} // anon namespace
> +
> +gimple_opt_pass *
> +make_pass_loop_split (gcc::context *ctxt)
> +{
> + return new pass_loop_split (ctxt);
> +}
> Index: doc/invoke.texi
> ===================================================================
> --- doc/invoke.texi (revision 231115)
> +++ doc/invoke.texi (working copy)
> @@ -446,7 +446,7 @@ Objective-C and Objective-C++ Dialects}.
> -fselective-scheduling -fselective-scheduling2 @gol
> -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
> -fsemantic-interposition -fshrink-wrap -fsignaling-nans @gol
> --fsingle-precision-constant -fsplit-ivs-in-unroller @gol
> +-fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops@gol
> -fsplit-paths @gol
> -fsplit-wide-types -fssa-backprop -fssa-phiopt @gol
> -fstack-protector -fstack-protector-all -fstack-protector-strong @gol
> @@ -10197,6 +10197,11 @@ Enabled with @option{-fprofile-use}.
> Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
> at level @option{-O1}
>
> +@item -fsplit-loops
> +@opindex fsplit-loops
> +Split a loop into two if it contains a condition that's always true
> +for one side of the iteration space and false for the other.
> +
> @item -funswitch-loops
> @opindex funswitch-loops
> Move branches with loop invariant conditions out of the loop, with duplicates
> Index: doc/passes.texi
> ===================================================================
> --- doc/passes.texi (revision 231115)
> +++ doc/passes.texi (working copy)
> @@ -484,6 +484,12 @@ out of the loops. To achieve this, a du
> each possible outcome of conditional jump(s). The pass is implemented in
> @file{tree-ssa-loop-unswitch.c}.
>
> +Loop splitting. If a loop contains a conditional statement that is
> +always true for one part of the iteration space and false for the other
> +this pass splits the loop into two, one dealing with one side the other
> +only with the other, thereby removing one inner-loop conditional. The
> +pass is implemented in @file{tree-ssa-loop-split.c}.
> +
> The optimizations also use various utility functions contained in
> @file{tree-ssa-loop-manip.c}, @file{cfgloop.c}, @file{cfgloopanal.c} and
> @file{cfgloopmanip.c}.
> Index: testsuite/gcc.dg/loop-split.c
> ===================================================================
> --- testsuite/gcc.dg/loop-split.c (revision 0)
> +++ testsuite/gcc.dg/loop-split.c (working copy)
> @@ -0,0 +1,147 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -fsplit-loops -fdump-tree-lsplit-details" } */
> +
> +#ifdef __cplusplus
> +extern "C" int printf (const char *, ...);
> +extern "C" void abort (void);
> +#else
> +extern int printf (const char *, ...);
> +extern void abort (void);
> +#endif
> +
> +/* Define TRACE to 1 or 2 to get detailed tracing.
> + Define SINGLE_TEST to 1 or 2 to get a simple routine with
> + just one loop, called only one time or with multiple parameters,
> + to make debugging easier. */
> +#ifndef TRACE
> +#define TRACE 0
> +#endif
> +
> +#define loop(beg,step,beg2,cond1,cond2) \
> + do \
> + { \
> + sum = 0; \
> + for (i = (beg), j = (beg2); (cond1); i+=(step),j+=(step)) \
> + { \
> + if (cond2) { \
> + if (TRACE > 1) printf ("a: %d %d\n", i, j); \
> + sum += a[i]; \
> + } else { \
> + if (TRACE > 1) printf ("b: %d %d\n", i, j); \
> + sum += b[i]; \
> + } \
> + } \
> + if (TRACE > 0) printf ("sum: %d\n", sum); \
> + check = check * 47 + sum; \
> + } while (0)
> +
> +#ifndef SINGLE_TEST
> +unsigned __attribute__((noinline, noclone)) dotest (int beg, int end, int step,
> + int c, int *a, int *b, int beg2)
> +{
> + unsigned check = 0;
> + int sum;
> + int i, j;
> + loop (beg, 1, beg2, i < end, j < c);
> + loop (beg, 1, beg2, i <= end, j < c);
> + loop (beg, 1, beg2, i < end, j <= c);
> + loop (beg, 1, beg2, i <= end, j <= c);
> + loop (beg, 1, beg2, i < end, j > c);
> + loop (beg, 1, beg2, i <= end, j > c);
> + loop (beg, 1, beg2, i < end, j >= c);
> + loop (beg, 1, beg2, i <= end, j >= c);
> + beg2 += end-beg;
> + loop (end, -1, beg2, i >= beg, j >= c);
> + loop (end, -1, beg2, i >= beg, j > c);
> + loop (end, -1, beg2, i > beg, j >= c);
> + loop (end, -1, beg2, i > beg, j > c);
> + loop (end, -1, beg2, i >= beg, j <= c);
> + loop (end, -1, beg2, i >= beg, j < c);
> + loop (end, -1, beg2, i > beg, j <= c);
> + loop (end, -1, beg2, i > beg, j < c);
> + return check;
> +}
> +
> +#else
> +
> +int __attribute__((noinline, noclone)) f (int beg, int end, int step,
> + int c, int *a, int *b, int beg2)
> +{
> + int sum = 0;
> + int i, j;
> + //for (i = beg, j = beg2; i < end; i += 1, j++ /*step*/)
> + for (i = end, j = beg2 + (end-beg); i > beg; i += -1, j-- /*step*/)
> + {
> + // i - j == X --> i = X + j
> + // --> i < end == X+j < end == j < end - X
> + // --> newend = end - (i_init - j_init)
> + // j < end-X && j < c --> j < min(end-X,c)
> + // j < end-X && j <= c --> j <= min(end-X-1,c) or j < min(end-X,c+1{OF!})
> + //if (j < c)
> + if (j >= c)
> + printf ("a: %d %d\n", i, j);
> + /*else
> + printf ("b: %d %d\n", i, j);*/
> + /*sum += a[i];
> + else
> + sum += b[i];*/
> + }
> + return sum;
> +}
> +
> +int __attribute__((noinline, noclone)) f2 (int *beg, int *end, int step,
> + int *c, int *a, int *b, int *beg2)
> +{
> + int sum = 0;
> + int *i, *j;
> + for (i = beg, j = beg2; i < end; i += 1, j++ /*step*/)
> + {
> + if (j <= c)
> + printf ("%d %d\n", i - beg, j - beg);
> + /*sum += a[i];
> + else
> + sum += b[i];*/
> + }
> + return sum;
> +}
> +#endif
> +
> +extern int printf (const char *, ...);
> +
> +int main ()
> +{
> + int a[] = {0,0,0,0,0, 1,2,3,4,5,6,7,8,9, 0,0,0,0,0};
> + int b[] = {0,0,0,0,0, -1,-2,-3,-4,-5,-6,-7,-8,-9, 0,0,0,0,0,};
> + int c;
> + int diff = 0;
> + unsigned check = 0;
> +#if defined(SINGLE_TEST) && (SINGLE_TEST == 1)
> + //dotest (0, 9, 1, -1, a+5, b+5, -1);
> + //return 0;
> + f (0, 9, 1, 5, a+5, b+5, -1);
> + return 0;
> +#endif
> + for (diff = -5; diff <= 5; diff++)
> + {
> + for (c = -1; c <= 10; c++)
> + {
> +#ifdef SINGLE_TEST
> + int s = f (0, 9, 1, c, a+5, b+5, diff);
> + //int s = f2 (a+0, a+9, 1, a+c, a+5, b+5, a+diff);
> + printf ("%d ", s);
> +#else
> + if (TRACE > 0)
> + printf ("check %d %d\n", c, diff);
> + check = check * 51 + dotest (0, 9, 1, c, a+5, b+5, diff);
> +#endif
> + }
> + //printf ("\n");
> + }
> + //printf ("%u\n", check);
> + if (check != 3213344948)
> + abort ();
> + return 0;
> +}
> +
> +/* All 16 loops in dotest should be split. */
> +/* { dg-final { scan-tree-dump-times "Loop split" 16 "lsplit" } } */