===================================================================
@@ -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.
===================================================================
@@ -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);
===================================================================
@@ -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)
===================================================================
@@ -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")
===================================================================
@@ -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);
===================================================================
@@ -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);
===================================================================
@@ -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 \
===================================================================
@@ -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);
+}
===================================================================
@@ -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
===================================================================
@@ -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}.
===================================================================
@@ -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" } } */