| /* Loop splitting. |
| Copyright (C) 2015-2020 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 "tree-inline.h" |
| #include "tree-cfgcleanup.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 two kinds of loop splitting. |
| |
| One 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 (class 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); |
| class loop *useloop = loop_containing_stmt (stmt); |
| |
| if (!simple_iv (loop, useloop, op0, iv, false)) |
| return NULL_TREE; |
| if (!simple_iv (loop, useloop, op1, &iv2, false)) |
| return NULL_TREE; |
| |
| /* Make it so that the first argument of the condition is |
| the looping one. */ |
| 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 (!iv->no_overflow) |
| 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 (class 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 = EDGE_SUCC (exit->src, EDGE_SUCC (exit->src, 0) == exit); |
| |
| 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 (class 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; |
| } |
| |
| /* Returns true if the exit values of all loop phi nodes can be |
| determined easily (i.e. that connect_loop_phis can determine them). */ |
| |
| static bool |
| easy_exit_values (class loop *loop) |
| { |
| edge exit = single_exit (loop); |
| edge latch = loop_latch_edge (loop); |
| gphi_iterator psi; |
| |
| /* Currently we regard the exit values as easy if they are the same |
| as the value over the backedge. Which is the case if the definition |
| of the backedge value dominates the exit edge. */ |
| for (psi = gsi_start_phis (loop->header); !gsi_end_p (psi); gsi_next (&psi)) |
| { |
| gphi *phi = psi.phi (); |
| tree next = PHI_ARG_DEF_FROM_EDGE (phi, latch); |
| basic_block bb; |
| if (TREE_CODE (next) == SSA_NAME |
| && (bb = gimple_bb (SSA_NAME_DEF_STMT (next))) |
| && !dominated_by_p (CDI_DOMINATORS, exit->src, bb)) |
| return false; |
| } |
| |
| return true; |
| } |
| |
| /* 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. The loops need to fulfill easy_exit_values(). */ |
| |
| static void |
| connect_loop_phis (class loop *loop1, class 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 (class loop *loop1, class 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->probability = profile_probability::likely (); |
| skip_e->probability = new_e->probability.invert (); |
| |
| 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, class 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 end-beg. */ |
| gimple_seq stmts2; |
| tree end = force_gimple_operand (niter->bound, &stmts2, |
| true, NULL_TREE); |
| gimple_seq_add_seq_without_update (stmts, stmts2); |
| if (POINTER_TYPE_P (TREE_TYPE (enddiff))) |
| { |
| tree tem = gimple_convert (stmts, sizetype, enddiff); |
| tem = gimple_build (stmts, NEGATE_EXPR, sizetype, tem); |
| enddiff = gimple_build (stmts, POINTER_PLUS_EXPR, |
| TREE_TYPE (enddiff), |
| end, tem); |
| } |
| else |
| enddiff = gimple_build (stmts, MINUS_EXPR, TREE_TYPE (enddiff), |
| end, enddiff); |
| |
| /* Compute guard_init + (end-beg). */ |
| tree newbound; |
| enddiff = gimple_convert (stmts, TREE_TYPE (guard_init), enddiff); |
| if (POINTER_TYPE_P (TREE_TYPE (guard_init))) |
| { |
| enddiff = gimple_convert (stmts, sizetype, enddiff); |
| newbound = gimple_build (stmts, POINTER_PLUS_EXPR, |
| TREE_TYPE (guard_init), |
| guard_init, enddiff); |
| } |
| else |
| newbound = gimple_build (stmts, PLUS_EXPR, TREE_TYPE (guard_init), |
| guard_init, 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 (class loop *loop1) |
| { |
| class tree_niter_desc niter; |
| basic_block *bbs; |
| unsigned i; |
| bool changed = false; |
| tree guard_iv; |
| tree border = NULL_TREE; |
| affine_iv iv; |
| |
| if (!single_exit (loop1) |
| /* ??? 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 (loop1->latch) |
| || !easy_exit_values (loop1) |
| || !number_of_iterations_exit (loop1, single_exit (loop1), &niter, |
| false, true) |
| || niter.cmp == ERROR_MARK |
| /* We can't yet handle loops controlled by a != predicate. */ |
| || niter.cmp == NE_EXPR) |
| return false; |
| |
| bbs = get_loop_body (loop1); |
| |
| if (!can_copy_bbs_p (bbs, loop1->num_nodes)) |
| { |
| free (bbs); |
| return false; |
| } |
| |
| /* 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; |
| |
| class loop *loop2 = loop_version (loop1, cond, &cond_bb, |
| profile_probability::always (), |
| profile_probability::always (), |
| profile_probability::always (), |
| profile_probability::always (), |
| 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; |
| } |
| |
| /* Another transformation of loops like: |
| |
| for (i = INIT (); CHECK (i); i = NEXT ()) |
| { |
| if (expr (a_1, a_2, ..., a_n)) // expr is pure |
| a_j = ...; // change at least one a_j |
| else |
| S; // not change any a_j |
| } |
| |
| into: |
| |
| for (i = INIT (); CHECK (i); i = NEXT ()) |
| { |
| if (expr (a_1, a_2, ..., a_n)) |
| a_j = ...; |
| else |
| { |
| S; |
| i = NEXT (); |
| break; |
| } |
| } |
| |
| for (; CHECK (i); i = NEXT ()) |
| { |
| S; |
| } |
| |
| */ |
| |
| /* Data structure to hold temporary information during loop split upon |
| semi-invariant conditional statement. */ |
| class split_info { |
| public: |
| /* Array of all basic blocks in a loop, returned by get_loop_body(). */ |
| basic_block *bbs; |
| |
| /* All memory store/clobber statements in a loop. */ |
| auto_vec<gimple *> memory_stores; |
| |
| /* Whether above memory stores vector has been filled. */ |
| int need_init; |
| |
| /* Control dependencies of basic blocks in a loop. */ |
| auto_vec<hash_set<basic_block> *> control_deps; |
| |
| split_info () : bbs (NULL), need_init (true) { } |
| |
| ~split_info () |
| { |
| if (bbs) |
| free (bbs); |
| |
| for (unsigned i = 0; i < control_deps.length (); i++) |
| delete control_deps[i]; |
| } |
| }; |
| |
| /* Find all statements with memory-write effect in LOOP, including memory |
| store and non-pure function call, and keep those in a vector. This work |
| is only done one time, for the vector should be constant during analysis |
| stage of semi-invariant condition. */ |
| |
| static void |
| find_vdef_in_loop (struct loop *loop) |
| { |
| split_info *info = (split_info *) loop->aux; |
| gphi *vphi = get_virtual_phi (loop->header); |
| |
| /* Indicate memory store vector has been filled. */ |
| info->need_init = false; |
| |
| /* If loop contains memory operation, there must be a virtual PHI node in |
| loop header basic block. */ |
| if (vphi == NULL) |
| return; |
| |
| /* All virtual SSA names inside the loop are connected to be a cyclic |
| graph via virtual PHI nodes. The virtual PHI node in loop header just |
| links the first and the last virtual SSA names, by using the last as |
| PHI operand to define the first. */ |
| const edge latch = loop_latch_edge (loop); |
| const tree first = gimple_phi_result (vphi); |
| const tree last = PHI_ARG_DEF_FROM_EDGE (vphi, latch); |
| |
| /* The virtual SSA cyclic graph might consist of only one SSA name, who |
| is defined by itself. |
| |
| .MEM_1 = PHI <.MEM_2(loop entry edge), .MEM_1(latch edge)> |
| |
| This means the loop contains only memory loads, so we can skip it. */ |
| if (first == last) |
| return; |
| |
| auto_vec<gimple *> other_stores; |
| auto_vec<tree> worklist; |
| auto_bitmap visited; |
| |
| bitmap_set_bit (visited, SSA_NAME_VERSION (first)); |
| bitmap_set_bit (visited, SSA_NAME_VERSION (last)); |
| worklist.safe_push (last); |
| |
| do |
| { |
| tree vuse = worklist.pop (); |
| gimple *stmt = SSA_NAME_DEF_STMT (vuse); |
| |
| /* We mark the first and last SSA names as visited at the beginning, |
| and reversely start the process from the last SSA name towards the |
| first, which ensures that this do-while will not touch SSA names |
| defined outside the loop. */ |
| gcc_assert (gimple_bb (stmt) |
| && flow_bb_inside_loop_p (loop, gimple_bb (stmt))); |
| |
| if (gimple_code (stmt) == GIMPLE_PHI) |
| { |
| gphi *phi = as_a <gphi *> (stmt); |
| |
| for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i) |
| { |
| tree arg = gimple_phi_arg_def (stmt, i); |
| |
| if (bitmap_set_bit (visited, SSA_NAME_VERSION (arg))) |
| worklist.safe_push (arg); |
| } |
| } |
| else |
| { |
| tree prev = gimple_vuse (stmt); |
| |
| /* Non-pure call statement is conservatively assumed to impact all |
| memory locations. So place call statements ahead of other memory |
| stores in the vector with an idea of using them as shortcut |
| terminators to memory alias analysis. */ |
| if (gimple_code (stmt) == GIMPLE_CALL) |
| info->memory_stores.safe_push (stmt); |
| else |
| other_stores.safe_push (stmt); |
| |
| if (bitmap_set_bit (visited, SSA_NAME_VERSION (prev))) |
| worklist.safe_push (prev); |
| } |
| } while (!worklist.is_empty ()); |
| |
| info->memory_stores.safe_splice (other_stores); |
| } |
| |
| /* Two basic blocks have equivalent control dependency if one dominates to |
| the other, and it is post-dominated by the latter. Given a basic block |
| BB in LOOP, find farest equivalent dominating basic block. For BB, there |
| is a constraint that BB does not post-dominate loop header of LOOP, this |
| means BB is control-dependent on at least one basic block in LOOP. */ |
| |
| static basic_block |
| get_control_equiv_head_block (struct loop *loop, basic_block bb) |
| { |
| while (!bb->aux) |
| { |
| basic_block dom_bb = get_immediate_dominator (CDI_DOMINATORS, bb); |
| |
| gcc_checking_assert (dom_bb && flow_bb_inside_loop_p (loop, dom_bb)); |
| |
| if (!dominated_by_p (CDI_POST_DOMINATORS, dom_bb, bb)) |
| break; |
| |
| bb = dom_bb; |
| } |
| return bb; |
| } |
| |
| /* Given a BB in LOOP, find out all basic blocks in LOOP that BB is control- |
| dependent on. */ |
| |
| static hash_set<basic_block> * |
| find_control_dep_blocks (struct loop *loop, basic_block bb) |
| { |
| /* BB has same control dependency as loop header, then it is not control- |
| dependent on any basic block in LOOP. */ |
| if (dominated_by_p (CDI_POST_DOMINATORS, loop->header, bb)) |
| return NULL; |
| |
| basic_block equiv_head = get_control_equiv_head_block (loop, bb); |
| |
| if (equiv_head->aux) |
| { |
| /* There is a basic block containing control dependency equivalent |
| to BB. No need to recompute that, and also set this information |
| to other equivalent basic blocks. */ |
| for (; bb != equiv_head; |
| bb = get_immediate_dominator (CDI_DOMINATORS, bb)) |
| bb->aux = equiv_head->aux; |
| return (hash_set<basic_block> *) equiv_head->aux; |
| } |
| |
| /* A basic block X is control-dependent on another Y iff there exists |
| a path from X to Y, in which every basic block other than X and Y |
| is post-dominated by Y, but X is not post-dominated by Y. |
| |
| According to this rule, traverse basic blocks in the loop backwards |
| starting from BB, if a basic block is post-dominated by BB, extend |
| current post-dominating path to this block, otherwise it is another |
| one that BB is control-dependent on. */ |
| |
| auto_vec<basic_block> pdom_worklist; |
| hash_set<basic_block> pdom_visited; |
| hash_set<basic_block> *dep_bbs = new hash_set<basic_block>; |
| |
| pdom_worklist.safe_push (equiv_head); |
| |
| do |
| { |
| basic_block pdom_bb = pdom_worklist.pop (); |
| edge_iterator ei; |
| edge e; |
| |
| if (pdom_visited.add (pdom_bb)) |
| continue; |
| |
| FOR_EACH_EDGE (e, ei, pdom_bb->preds) |
| { |
| basic_block pred_bb = e->src; |
| |
| if (!dominated_by_p (CDI_POST_DOMINATORS, pred_bb, bb)) |
| { |
| dep_bbs->add (pred_bb); |
| continue; |
| } |
| |
| pred_bb = get_control_equiv_head_block (loop, pred_bb); |
| |
| if (pdom_visited.contains (pred_bb)) |
| continue; |
| |
| if (!pred_bb->aux) |
| { |
| pdom_worklist.safe_push (pred_bb); |
| continue; |
| } |
| |
| /* If control dependency of basic block is available, fast extend |
| post-dominating path using the information instead of advancing |
| forward step-by-step. */ |
| hash_set<basic_block> *pred_dep_bbs |
| = (hash_set<basic_block> *) pred_bb->aux; |
| |
| for (hash_set<basic_block>::iterator iter = pred_dep_bbs->begin (); |
| iter != pred_dep_bbs->end (); ++iter) |
| { |
| basic_block pred_dep_bb = *iter; |
| |
| /* Basic blocks can either be in control dependency of BB, or |
| must be post-dominated by BB, if so, extend the path from |
| these basic blocks. */ |
| if (!dominated_by_p (CDI_POST_DOMINATORS, pred_dep_bb, bb)) |
| dep_bbs->add (pred_dep_bb); |
| else if (!pdom_visited.contains (pred_dep_bb)) |
| pdom_worklist.safe_push (pred_dep_bb); |
| } |
| } |
| } while (!pdom_worklist.is_empty ()); |
| |
| /* Record computed control dependencies in loop so that we can reach them |
| when reclaiming resources. */ |
| ((split_info *) loop->aux)->control_deps.safe_push (dep_bbs); |
| |
| /* Associate control dependence with related equivalent basic blocks. */ |
| for (equiv_head->aux = dep_bbs; bb != equiv_head; |
| bb = get_immediate_dominator (CDI_DOMINATORS, bb)) |
| bb->aux = dep_bbs; |
| |
| return dep_bbs; |
| } |
| |
| /* Forward declaration */ |
| |
| static bool |
| stmt_semi_invariant_p_1 (struct loop *loop, gimple *stmt, |
| const_basic_block skip_head, |
| hash_map<gimple *, bool> &stmt_stat); |
| |
| /* Given STMT, memory load or pure call statement, check whether it is impacted |
| by some memory store in LOOP, excluding trace starting from SKIP_HEAD (the |
| trace is composed of SKIP_HEAD and those basic block dominated by it, always |
| corresponds to one branch of a conditional statement). If SKIP_HEAD is |
| NULL, all basic blocks of LOOP are checked. */ |
| |
| static bool |
| vuse_semi_invariant_p (struct loop *loop, gimple *stmt, |
| const_basic_block skip_head) |
| { |
| split_info *info = (split_info *) loop->aux; |
| tree rhs = NULL_TREE; |
| ao_ref ref; |
| gimple *store; |
| unsigned i; |
| |
| /* Collect memory store/clobber statements if haven't done that. */ |
| if (info->need_init) |
| find_vdef_in_loop (loop); |
| |
| if (is_gimple_assign (stmt)) |
| rhs = gimple_assign_rhs1 (stmt); |
| |
| ao_ref_init (&ref, rhs); |
| |
| FOR_EACH_VEC_ELT (info->memory_stores, i, store) |
| { |
| /* Skip basic blocks dominated by SKIP_HEAD, if non-NULL. */ |
| if (skip_head |
| && dominated_by_p (CDI_DOMINATORS, gimple_bb (store), skip_head)) |
| continue; |
| |
| if (!ref.ref || stmt_may_clobber_ref_p_1 (store, &ref)) |
| return false; |
| } |
| |
| return true; |
| } |
| |
| /* Suppose one condition branch, led by SKIP_HEAD, is not executed since |
| certain iteration of LOOP, check whether an SSA name (NAME) remains |
| unchanged in next iteration. We call this characteristic semi- |
| invariantness. SKIP_HEAD might be NULL, if so, nothing excluded, all basic |
| blocks and control flows in the loop will be considered. Semi-invariant |
| state of checked statement is cached in hash map STMT_STAT to avoid |
| redundant computation in possible following re-check. */ |
| |
| static inline bool |
| ssa_semi_invariant_p (struct loop *loop, tree name, |
| const_basic_block skip_head, |
| hash_map<gimple *, bool> &stmt_stat) |
| { |
| gimple *def = SSA_NAME_DEF_STMT (name); |
| const_basic_block def_bb = gimple_bb (def); |
| |
| /* An SSA name defined outside loop is definitely semi-invariant. */ |
| if (!def_bb || !flow_bb_inside_loop_p (loop, def_bb)) |
| return true; |
| |
| if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (name)) |
| return false; |
| |
| return stmt_semi_invariant_p_1 (loop, def, skip_head, stmt_stat); |
| } |
| |
| /* Check whether a loop iteration PHI node (LOOP_PHI) defines a value that is |
| semi-invariant in LOOP. Basic blocks dominated by SKIP_HEAD (if non-NULL), |
| are excluded from LOOP. */ |
| |
| static bool |
| loop_iter_phi_semi_invariant_p (struct loop *loop, gphi *loop_phi, |
| const_basic_block skip_head) |
| { |
| const_edge latch = loop_latch_edge (loop); |
| tree name = gimple_phi_result (loop_phi); |
| tree from = PHI_ARG_DEF_FROM_EDGE (loop_phi, latch); |
| |
| gcc_checking_assert (from); |
| |
| /* Loop iteration PHI node locates in loop header, and it has two source |
| operands, one is an initial value coming from outside the loop, the other |
| is a value through latch of the loop, which is derived in last iteration, |
| we call the latter latch value. From the PHI node to definition of latch |
| value, if excluding branch trace starting from SKIP_HEAD, except copy- |
| assignment or likewise, there is no other kind of value redefinition, SSA |
| name defined by the PHI node is semi-invariant. |
| |
| loop entry |
| | .--- latch ---. |
| | | | |
| v v | |
| x_1 = PHI <x_0, x_3> | |
| | | |
| v | |
| .------- if (cond) -------. | |
| | | | |
| | [ SKIP ] | |
| | | | |
| | x_2 = ... | |
| | | | |
| '---- T ---->.<---- F ----' | |
| | | |
| v | |
| x_3 = PHI <x_1, x_2> | |
| | | |
| '----------------------' |
| |
| Suppose in certain iteration, execution flow in above graph goes through |
| true branch, which means that one source value to define x_3 in false |
| branch (x_2) is skipped, x_3 only comes from x_1, and x_1 in next |
| iterations is defined by x_3, we know that x_1 will never changed if COND |
| always chooses true branch from then on. */ |
| |
| while (from != name) |
| { |
| /* A new value comes from a CONSTANT. */ |
| if (TREE_CODE (from) != SSA_NAME) |
| return false; |
| |
| gimple *stmt = SSA_NAME_DEF_STMT (from); |
| const_basic_block bb = gimple_bb (stmt); |
| |
| /* A new value comes from outside the loop. */ |
| if (!bb || !flow_bb_inside_loop_p (loop, bb)) |
| return false; |
| |
| from = NULL_TREE; |
| |
| if (gimple_code (stmt) == GIMPLE_PHI) |
| { |
| gphi *phi = as_a <gphi *> (stmt); |
| |
| for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i) |
| { |
| if (skip_head) |
| { |
| const_edge e = gimple_phi_arg_edge (phi, i); |
| |
| /* Don't consider redefinitions in excluded basic blocks. */ |
| if (dominated_by_p (CDI_DOMINATORS, e->src, skip_head)) |
| continue; |
| } |
| |
| tree arg = gimple_phi_arg_def (phi, i); |
| |
| if (!from) |
| from = arg; |
| else if (!operand_equal_p (from, arg, 0)) |
| /* There are more than one source operands that provide |
| different values to the SSA name, it is variant. */ |
| return false; |
| } |
| } |
| else if (gimple_code (stmt) == GIMPLE_ASSIGN) |
| { |
| /* For simple value copy, check its rhs instead. */ |
| if (gimple_assign_ssa_name_copy_p (stmt)) |
| from = gimple_assign_rhs1 (stmt); |
| } |
| |
| /* Any other kind of definition is deemed to introduce a new value |
| to the SSA name. */ |
| if (!from) |
| return false; |
| } |
| return true; |
| } |
| |
| /* Check whether conditional predicates that BB is control-dependent on, are |
| semi-invariant in LOOP. Basic blocks dominated by SKIP_HEAD (if non-NULL), |
| are excluded from LOOP. Semi-invariant state of checked statement is cached |
| in hash map STMT_STAT. */ |
| |
| static bool |
| control_dep_semi_invariant_p (struct loop *loop, basic_block bb, |
| const_basic_block skip_head, |
| hash_map<gimple *, bool> &stmt_stat) |
| { |
| hash_set<basic_block> *dep_bbs = find_control_dep_blocks (loop, bb); |
| |
| if (!dep_bbs) |
| return true; |
| |
| for (hash_set<basic_block>::iterator iter = dep_bbs->begin (); |
| iter != dep_bbs->end (); ++iter) |
| { |
| gimple *last = last_stmt (*iter); |
| |
| if (!last) |
| return false; |
| |
| /* Only check condition predicates. */ |
| if (gimple_code (last) != GIMPLE_COND |
| && gimple_code (last) != GIMPLE_SWITCH) |
| return false; |
| |
| if (!stmt_semi_invariant_p_1 (loop, last, skip_head, stmt_stat)) |
| return false; |
| } |
| |
| return true; |
| } |
| |
| /* Check whether STMT is semi-invariant in LOOP, iff all its operands are |
| semi-invariant, consequently, all its defined values are semi-invariant. |
| Basic blocks dominated by SKIP_HEAD (if non-NULL), are excluded from LOOP. |
| Semi-invariant state of checked statement is cached in hash map |
| STMT_STAT. */ |
| |
| static bool |
| stmt_semi_invariant_p_1 (struct loop *loop, gimple *stmt, |
| const_basic_block skip_head, |
| hash_map<gimple *, bool> &stmt_stat) |
| { |
| bool existed; |
| bool &invar = stmt_stat.get_or_insert (stmt, &existed); |
| |
| if (existed) |
| return invar; |
| |
| /* A statement might depend on itself, which is treated as variant. So set |
| state of statement under check to be variant to ensure that. */ |
| invar = false; |
| |
| if (gimple_code (stmt) == GIMPLE_PHI) |
| { |
| gphi *phi = as_a <gphi *> (stmt); |
| |
| if (gimple_bb (stmt) == loop->header) |
| { |
| /* If the entry value is subject to abnormal coalescing |
| avoid the transform since we're going to duplicate the |
| loop header and thus likely introduce overlapping life-ranges |
| between the PHI def and the entry on the path when the |
| first loop is skipped. */ |
| tree entry_def |
| = PHI_ARG_DEF_FROM_EDGE (phi, loop_preheader_edge (loop)); |
| if (TREE_CODE (entry_def) == SSA_NAME |
| && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (entry_def)) |
| return false; |
| invar = loop_iter_phi_semi_invariant_p (loop, phi, skip_head); |
| return invar; |
| } |
| |
| /* For a loop PHI node that does not locate in loop header, it is semi- |
| invariant only if two conditions are met. The first is its source |
| values are derived from CONSTANT (including loop-invariant value), or |
| from SSA name defined by semi-invariant loop iteration PHI node. The |
| second is its source incoming edges are control-dependent on semi- |
| invariant conditional predicates. */ |
| for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i) |
| { |
| const_edge e = gimple_phi_arg_edge (phi, i); |
| tree arg = gimple_phi_arg_def (phi, i); |
| |
| if (TREE_CODE (arg) == SSA_NAME) |
| { |
| if (!ssa_semi_invariant_p (loop, arg, skip_head, stmt_stat)) |
| return false; |
| |
| /* If source value is defined in location from where the source |
| edge comes in, no need to check control dependency again |
| since this has been done in above SSA name check stage. */ |
| if (e->src == gimple_bb (SSA_NAME_DEF_STMT (arg))) |
| continue; |
| } |
| |
| if (!control_dep_semi_invariant_p (loop, e->src, skip_head, |
| stmt_stat)) |
| return false; |
| } |
| } |
| else |
| { |
| ssa_op_iter iter; |
| tree use; |
| |
| /* Volatile memory load or return of normal (non-const/non-pure) call |
| should not be treated as constant in each iteration of loop. */ |
| if (gimple_has_side_effects (stmt)) |
| return false; |
| |
| /* Check if any memory store may kill memory load at this place. */ |
| if (gimple_vuse (stmt) && !vuse_semi_invariant_p (loop, stmt, skip_head)) |
| return false; |
| |
| /* Although operand of a statement might be SSA name, CONSTANT or |
| VARDECL, here we only need to check SSA name operands. This is |
| because check on VARDECL operands, which involve memory loads, |
| must have been done prior to invocation of this function in |
| vuse_semi_invariant_p. */ |
| FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE) |
| if (!ssa_semi_invariant_p (loop, use, skip_head, stmt_stat)) |
| return false; |
| } |
| |
| if (!control_dep_semi_invariant_p (loop, gimple_bb (stmt), skip_head, |
| stmt_stat)) |
| return false; |
| |
| /* Here we SHOULD NOT use invar = true, since hash map might be changed due |
| to new insertion, and thus invar may point to invalid memory. */ |
| stmt_stat.put (stmt, true); |
| return true; |
| } |
| |
| /* A helper function to check whether STMT is semi-invariant in LOOP. Basic |
| blocks dominated by SKIP_HEAD (if non-NULL), are excluded from LOOP. */ |
| |
| static bool |
| stmt_semi_invariant_p (struct loop *loop, gimple *stmt, |
| const_basic_block skip_head) |
| { |
| hash_map<gimple *, bool> stmt_stat; |
| return stmt_semi_invariant_p_1 (loop, stmt, skip_head, stmt_stat); |
| } |
| |
| /* Determine when conditional statement never transfers execution to one of its |
| branch, whether we can remove the branch's leading basic block (BRANCH_BB) |
| and those basic blocks dominated by BRANCH_BB. */ |
| |
| static bool |
| branch_removable_p (basic_block branch_bb) |
| { |
| edge_iterator ei; |
| edge e; |
| |
| if (single_pred_p (branch_bb)) |
| return true; |
| |
| FOR_EACH_EDGE (e, ei, branch_bb->preds) |
| { |
| if (dominated_by_p (CDI_DOMINATORS, e->src, branch_bb)) |
| continue; |
| |
| if (dominated_by_p (CDI_DOMINATORS, branch_bb, e->src)) |
| continue; |
| |
| /* The branch can be reached from opposite branch, or from some |
| statement not dominated by the conditional statement. */ |
| return false; |
| } |
| |
| return true; |
| } |
| |
| /* Find out which branch of a conditional statement (COND) is invariant in the |
| execution context of LOOP. That is: once the branch is selected in certain |
| iteration of the loop, any operand that contributes to computation of the |
| conditional statement remains unchanged in all following iterations. */ |
| |
| static edge |
| get_cond_invariant_branch (struct loop *loop, gcond *cond) |
| { |
| basic_block cond_bb = gimple_bb (cond); |
| basic_block targ_bb[2]; |
| bool invar[2]; |
| unsigned invar_checks = 0; |
| |
| for (unsigned i = 0; i < 2; i++) |
| { |
| targ_bb[i] = EDGE_SUCC (cond_bb, i)->dest; |
| |
| /* One branch directs to loop exit, no need to perform loop split upon |
| this conditional statement. Firstly, it is trivial if the exit branch |
| is semi-invariant, for the statement is just to break loop. Secondly, |
| if the opposite branch is semi-invariant, it means that the statement |
| is real loop-invariant, which is covered by loop unswitch. */ |
| if (!flow_bb_inside_loop_p (loop, targ_bb[i])) |
| return NULL; |
| } |
| |
| for (unsigned i = 0; i < 2; i++) |
| { |
| invar[!i] = false; |
| |
| if (!branch_removable_p (targ_bb[i])) |
| continue; |
| |
| /* Given a semi-invariant branch, if its opposite branch dominates |
| loop latch, it and its following trace will only be executed in |
| final iteration of loop, namely it is not part of repeated body |
| of the loop. Similar to the above case that the branch is loop |
| exit, no need to split loop. */ |
| if (dominated_by_p (CDI_DOMINATORS, loop->latch, targ_bb[i])) |
| continue; |
| |
| invar[!i] = stmt_semi_invariant_p (loop, cond, targ_bb[i]); |
| invar_checks++; |
| } |
| |
| /* With both branches being invariant (handled by loop unswitch) or |
| variant is not what we want. */ |
| if (invar[0] ^ !invar[1]) |
| return NULL; |
| |
| /* Found a real loop-invariant condition, do nothing. */ |
| if (invar_checks < 2 && stmt_semi_invariant_p (loop, cond, NULL)) |
| return NULL; |
| |
| return EDGE_SUCC (cond_bb, invar[0] ? 0 : 1); |
| } |
| |
| /* Calculate increased code size measured by estimated insn number if applying |
| loop split upon certain branch (BRANCH_EDGE) of a conditional statement. */ |
| |
| static int |
| compute_added_num_insns (struct loop *loop, const_edge branch_edge) |
| { |
| basic_block cond_bb = branch_edge->src; |
| unsigned branch = EDGE_SUCC (cond_bb, 1) == branch_edge; |
| basic_block opposite_bb = EDGE_SUCC (cond_bb, !branch)->dest; |
| basic_block *bbs = ((split_info *) loop->aux)->bbs; |
| int num = 0; |
| |
| for (unsigned i = 0; i < loop->num_nodes; i++) |
| { |
| /* Do no count basic blocks only in opposite branch. */ |
| if (dominated_by_p (CDI_DOMINATORS, bbs[i], opposite_bb)) |
| continue; |
| |
| num += estimate_num_insns_seq (bb_seq (bbs[i]), &eni_size_weights); |
| } |
| |
| /* It is unnecessary to evaluate expression of the conditional statement |
| in new loop that contains only invariant branch. This expression should |
| be constant value (either true or false). Exclude code size of insns |
| that contribute to computation of the expression. */ |
| |
| auto_vec<gimple *> worklist; |
| hash_set<gimple *> removed; |
| gimple *stmt = last_stmt (cond_bb); |
| |
| worklist.safe_push (stmt); |
| removed.add (stmt); |
| num -= estimate_num_insns (stmt, &eni_size_weights); |
| |
| do |
| { |
| ssa_op_iter opnd_iter; |
| use_operand_p opnd_p; |
| |
| stmt = worklist.pop (); |
| FOR_EACH_PHI_OR_STMT_USE (opnd_p, stmt, opnd_iter, SSA_OP_USE) |
| { |
| tree opnd = USE_FROM_PTR (opnd_p); |
| |
| if (TREE_CODE (opnd) != SSA_NAME || SSA_NAME_IS_DEFAULT_DEF (opnd)) |
| continue; |
| |
| gimple *opnd_stmt = SSA_NAME_DEF_STMT (opnd); |
| use_operand_p use_p; |
| imm_use_iterator use_iter; |
| |
| if (removed.contains (opnd_stmt) |
| || !flow_bb_inside_loop_p (loop, gimple_bb (opnd_stmt))) |
| continue; |
| |
| FOR_EACH_IMM_USE_FAST (use_p, use_iter, opnd) |
| { |
| gimple *use_stmt = USE_STMT (use_p); |
| |
| if (!is_gimple_debug (use_stmt) && !removed.contains (use_stmt)) |
| { |
| opnd_stmt = NULL; |
| break; |
| } |
| } |
| |
| if (opnd_stmt) |
| { |
| worklist.safe_push (opnd_stmt); |
| removed.add (opnd_stmt); |
| num -= estimate_num_insns (opnd_stmt, &eni_size_weights); |
| } |
| } |
| } while (!worklist.is_empty ()); |
| |
| gcc_assert (num >= 0); |
| return num; |
| } |
| |
| /* Find out loop-invariant branch of a conditional statement (COND) if it has, |
| and check whether it is eligible and profitable to perform loop split upon |
| this branch in LOOP. */ |
| |
| static edge |
| get_cond_branch_to_split_loop (struct loop *loop, gcond *cond) |
| { |
| edge invar_branch = get_cond_invariant_branch (loop, cond); |
| if (!invar_branch) |
| return NULL; |
| |
| /* When accurate profile information is available, and execution |
| frequency of the branch is too low, just let it go. */ |
| profile_probability prob = invar_branch->probability; |
| if (prob.reliable_p ()) |
| { |
| int thres = param_min_loop_cond_split_prob; |
| |
| if (prob < profile_probability::always ().apply_scale (thres, 100)) |
| return NULL; |
| } |
| |
| /* Add a threshold for increased code size to disable loop split. */ |
| if (compute_added_num_insns (loop, invar_branch) > param_max_peeled_insns) |
| return NULL; |
| |
| return invar_branch; |
| } |
| |
| /* Given a loop (LOOP1) with a loop-invariant branch (INVAR_BRANCH) of some |
| conditional statement, perform loop split transformation illustrated |
| as the following graph. |
| |
| .-------T------ if (true) ------F------. |
| | .---------------. | |
| | | | | |
| v | v v |
| pre-header | pre-header |
| | .------------. | | .------------. |
| | | | | | | | |
| | v | | | v | |
| header | | header | |
| | | | | | |
| .--- if (cond) ---. | | .--- if (true) ---. | |
| | | | | | | | |
| invariant | | | invariant | | |
| | | | | | | | |
| '---T--->.<---F---' | | '---T--->.<---F---' | |
| | | / | | |
| stmts | / stmts | |
| | F T | | |
| / \ | / / \ | |
| .-------* * [ if (cond) ] .-------* * | |
| | | | | | | |
| | latch | | latch | |
| | | | | | | |
| | '------------' | '------------' |
| '------------------------. .-----------' |
| loop1 | | loop2 |
| v v |
| exits |
| |
| In the graph, loop1 represents the part derived from original one, and |
| loop2 is duplicated using loop_version (), which corresponds to the part |
| of original one being splitted out. In original latch edge of loop1, we |
| insert a new conditional statement duplicated from the semi-invariant cond, |
| and one of its branch goes back to loop1 header as a latch edge, and the |
| other branch goes to loop2 pre-header as an entry edge. And also in loop2, |
| we abandon the variant branch of the conditional statement by setting a |
| constant bool condition, based on which branch is semi-invariant. */ |
| |
| static bool |
| do_split_loop_on_cond (struct loop *loop1, edge invar_branch) |
| { |
| basic_block cond_bb = invar_branch->src; |
| bool true_invar = !!(invar_branch->flags & EDGE_TRUE_VALUE); |
| gcond *cond = as_a <gcond *> (last_stmt (cond_bb)); |
| |
| gcc_assert (cond_bb->loop_father == loop1); |
| |
| if (dump_enabled_p ()) |
| dump_printf_loc (MSG_OPTIMIZED_LOCATIONS, cond, |
| "loop split on semi-invariant condition at %s branch\n", |
| true_invar ? "true" : "false"); |
| |
| initialize_original_copy_tables (); |
| |
| struct loop *loop2 = loop_version (loop1, boolean_true_node, NULL, |
| profile_probability::always (), |
| profile_probability::never (), |
| profile_probability::always (), |
| profile_probability::always (), |
| true); |
| if (!loop2) |
| { |
| free_original_copy_tables (); |
| return false; |
| } |
| |
| basic_block cond_bb_copy = get_bb_copy (cond_bb); |
| gcond *cond_copy = as_a<gcond *> (last_stmt (cond_bb_copy)); |
| |
| /* Replace the condition in loop2 with a bool constant to let PassManager |
| remove the variant branch after current pass completes. */ |
| if (true_invar) |
| gimple_cond_make_true (cond_copy); |
| else |
| gimple_cond_make_false (cond_copy); |
| |
| update_stmt (cond_copy); |
| |
| /* Insert a new conditional statement on latch edge of loop1, its condition |
| is duplicated from the semi-invariant. This statement acts as a switch |
| to transfer execution from loop1 to loop2, when loop1 enters into |
| invariant state. */ |
| basic_block latch_bb = split_edge (loop_latch_edge (loop1)); |
| basic_block break_bb = split_edge (single_pred_edge (latch_bb)); |
| gimple *break_cond = gimple_build_cond (gimple_cond_code(cond), |
| gimple_cond_lhs (cond), |
| gimple_cond_rhs (cond), |
| NULL_TREE, NULL_TREE); |
| |
| gimple_stmt_iterator gsi = gsi_last_bb (break_bb); |
| gsi_insert_after (&gsi, break_cond, GSI_NEW_STMT); |
| |
| edge to_loop1 = single_succ_edge (break_bb); |
| edge to_loop2 = make_edge (break_bb, loop_preheader_edge (loop2)->src, 0); |
| |
| to_loop1->flags &= ~EDGE_FALLTHRU; |
| to_loop1->flags |= true_invar ? EDGE_FALSE_VALUE : EDGE_TRUE_VALUE; |
| to_loop2->flags |= true_invar ? EDGE_TRUE_VALUE : EDGE_FALSE_VALUE; |
| |
| update_ssa (TODO_update_ssa); |
| |
| /* Due to introduction of a control flow edge from loop1 latch to loop2 |
| pre-header, we should update PHIs in loop2 to reflect this connection |
| between loop1 and loop2. */ |
| connect_loop_phis (loop1, loop2, to_loop2); |
| |
| free_original_copy_tables (); |
| |
| rewrite_into_loop_closed_ssa_1 (NULL, 0, SSA_OP_USE, loop1); |
| |
| return true; |
| } |
| |
| /* Traverse all conditional statements in LOOP, to find out a good candidate |
| upon which we can do loop split. */ |
| |
| static bool |
| split_loop_on_cond (struct loop *loop) |
| { |
| split_info *info = new split_info (); |
| basic_block *bbs = info->bbs = get_loop_body (loop); |
| bool do_split = false; |
| |
| /* Allocate an area to keep temporary info, and associate its address |
| with loop aux field. */ |
| loop->aux = info; |
| |
| for (unsigned i = 0; i < loop->num_nodes; i++) |
| bbs[i]->aux = NULL; |
| |
| for (unsigned i = 0; i < loop->num_nodes; i++) |
| { |
| basic_block bb = bbs[i]; |
| |
| /* We only consider conditional statement, which be executed at most once |
| in each iteration of the loop. So skip statements in inner loops. */ |
| if ((bb->loop_father != loop) || (bb->flags & BB_IRREDUCIBLE_LOOP)) |
| continue; |
| |
| /* Actually this check is not a must constraint. With it, we can ensure |
| conditional statement will always be executed in each iteration. */ |
| if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb)) |
| continue; |
| |
| gimple *last = last_stmt (bb); |
| |
| if (!last || gimple_code (last) != GIMPLE_COND) |
| continue; |
| |
| gcond *cond = as_a <gcond *> (last); |
| edge branch_edge = get_cond_branch_to_split_loop (loop, cond); |
| |
| if (branch_edge) |
| { |
| do_split_loop_on_cond (loop, branch_edge); |
| do_split = true; |
| break; |
| } |
| } |
| |
| delete info; |
| loop->aux = NULL; |
| |
| return do_split; |
| } |
| |
| /* Main entry point. Perform loop splitting on all suitable loops. */ |
| |
| static unsigned int |
| tree_ssa_split_loops (void) |
| { |
| class loop *loop; |
| bool changed = false; |
| |
| gcc_assert (scev_initialized_p ()); |
| |
| calculate_dominance_info (CDI_POST_DOMINATORS); |
| |
| FOR_EACH_LOOP (loop, LI_INCLUDE_ROOT) |
| loop->aux = NULL; |
| |
| /* Go through all loops starting from innermost. */ |
| FOR_EACH_LOOP (loop, LI_FROM_INNERMOST) |
| { |
| 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 (optimize_loop_for_size_p (loop)) |
| continue; |
| |
| if (split_loop (loop) || split_loop_on_cond (loop)) |
| { |
| /* Mark our containing loop as having had some split inner loops. */ |
| loop_outer (loop)->aux = loop; |
| changed = true; |
| } |
| } |
| |
| FOR_EACH_LOOP (loop, LI_INCLUDE_ROOT) |
| loop->aux = NULL; |
| |
| clear_aux_for_blocks (); |
| |
| free_dominance_info (CDI_POST_DOMINATORS); |
| |
| 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); |
| } |