On Tue, Jul 26, 2016 at 4:32 AM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Mon, Jul 25, 2016 at 10:57 PM, Andrew Pinski <pins...@gmail.com> wrote:
>> On Wed, Dec 2, 2015 at 5:23 AM, Michael Matz <m...@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.
>
> I think scev_cprop needs to be re-written to an utility so that the vectorizer
> itself can (within its own cost-model) eliminate an induction using it.
>
> Richard.
>
>> 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;
>> + }
>
> How does the iterator not visit loop_outer (loop)?!
The iterator with flags of 0 does not visit the the root. So the way
to fix this is change 0 (which is the flags) with LI_INCLUDE_ROOT so
we zero out the root too.
Thanks,
Andrew
>
>>
>> /* 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" } } */
