From 095f78c62157124ad479a3f98b6995ced090b807 Mon Sep 17 00:00:00 2001 From: Feng Xue Date: Thu, 7 Nov 2019 15:43:01 +0000 Subject: [PATCH] Loop split on semi-invariant conditional statement 2019-11-07 Feng Xue PR tree-optimization/89134 * doc/invoke.texi (min-loop-cond-split-prob): Document new --params. * params.def: Add min-loop-cond-split-prob. * tree-ssa-loop-split.c (split_loop): Remove niter parameter, move some outside checks on loop into the function. (split_info): New class. (find_vdef_in_loop, get_control_equiv_head_block): New functions. (find_control_dep_blocks, vuse_semi_invariant_p): Likewise. (ssa_semi_invariant_p, loop_iter_phi_semi_invariant_p): Likewise. (control_dep_semi_invariant_p, stmt_semi_invariant_p_1): Likewise. (stmt_semi_invariant_p, branch_removable_p): Likewise. (get_cond_invariant_branch, compute_added_num_insns): Likewise. (get_cond_branch_to_split_loop, do_split_loop_on_cond): Likewise. (split_loop_on_cond): Likewise. (tree_ssa_split_loops): Add loop split on conditional statement. 2019-11-07 Feng Xue PR tree-optimization/89134 * gcc.dg/tree-ssa/loop-cond-split-1.c: New test. * g++.dg/tree-ssa/loop-cond-split-1.C: New test. * gcc.dg/torture/pr55107.c: Add -fno-split-loops. From-SVN: r277923 --- gcc/ChangeLog | 18 + gcc/doc/invoke.texi | 5 + gcc/params.def | 6 + gcc/testsuite/ChangeLog | 7 + .../g++.dg/tree-ssa/loop-cond-split-1.C | 33 + gcc/testsuite/gcc.dg/torture/pr55107.c | 1 + .../gcc.dg/tree-ssa/loop-cond-split-1.c | 97 ++ gcc/tree-ssa-loop-split.c | 1023 ++++++++++++++++- 8 files changed, 1162 insertions(+), 28 deletions(-) create mode 100644 gcc/testsuite/g++.dg/tree-ssa/loop-cond-split-1.C create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/loop-cond-split-1.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index aba47075c0a..d3ef9311126 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,21 @@ +2019-11-07 Feng Xue + + PR tree-optimization/89134 + * doc/invoke.texi (min-loop-cond-split-prob): Document new --params. + * params.def: Add min-loop-cond-split-prob. + * tree-ssa-loop-split.c (split_loop): Remove niter parameter, move some + outside checks on loop into the function. + (split_info): New class. + (find_vdef_in_loop, get_control_equiv_head_block): New functions. + (find_control_dep_blocks, vuse_semi_invariant_p): Likewise. + (ssa_semi_invariant_p, loop_iter_phi_semi_invariant_p): Likewise. + (control_dep_semi_invariant_p, stmt_semi_invariant_p_1): Likewise. + (stmt_semi_invariant_p, branch_removable_p): Likewise. + (get_cond_invariant_branch, compute_added_num_insns): Likewise. + (get_cond_branch_to_split_loop, do_split_loop_on_cond): Likewise. + (split_loop_on_cond): Likewise. + (tree_ssa_split_loops): Add loop split on conditional statement. + 2019-11-07 Andreas Krebbel * config/s390/s390.md ("*cstorecc_z13"): New insn_and_split diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 42db3287cae..15fe2284d42 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -11517,6 +11517,11 @@ The maximum number of branches unswitched in a single loop. @item lim-expensive The minimum cost of an expensive expression in the loop invariant motion. +@item min-loop-cond-split-prob +When FDO profile information is available, @option{min-loop-cond-split-prob} +specifies minimum threshold for probability of semi-invariant condition +statement to trigger loop split. + @item iv-consider-all-candidates-bound Bound on number of candidates for induction variables, below which all candidates are considered for each use in induction variable diff --git a/gcc/params.def b/gcc/params.def index 942447d77e6..df7d1f7c5e7 100644 --- a/gcc/params.def +++ b/gcc/params.def @@ -415,6 +415,12 @@ DEFPARAM(PARAM_MAX_UNSWITCH_LEVEL, "The maximum number of unswitchings in a single loop.", 3, 0, 0) +DEFPARAM(PARAM_MIN_LOOP_COND_SPLIT_PROB, + "min-loop-cond-split-prob", + "The minimum threshold for probability of semi-invariant condition " + "statement to trigger loop split.", + 30, 0, 100) + /* The maximum number of insns in loop header duplicated by the copy loop headers pass. */ DEFPARAM(PARAM_MAX_LOOP_HEADER_INSNS, diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index b42b78b4d39..c80457cca9e 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,10 @@ +2019-11-07 Feng Xue + + PR tree-optimization/89134 + * gcc.dg/tree-ssa/loop-cond-split-1.c: New test. + * g++.dg/tree-ssa/loop-cond-split-1.C: New test. + * gcc.dg/torture/pr55107.c: Add -fno-split-loops. + 2019-11-07 Andreas Krebbel * gcc.target/s390/addsub-signed-overflow-1.c: Expect lochi diff --git a/gcc/testsuite/g++.dg/tree-ssa/loop-cond-split-1.C b/gcc/testsuite/g++.dg/tree-ssa/loop-cond-split-1.C new file mode 100644 index 00000000000..0d679cb9035 --- /dev/null +++ b/gcc/testsuite/g++.dg/tree-ssa/loop-cond-split-1.C @@ -0,0 +1,33 @@ +/* { dg-do compile } */ +/* { dg-options "-O3 -fdump-tree-lsplit-details" } */ + +#include +#include + +using namespace std; + +class A +{ +public: + bool empty; + void set (string s); +}; + +class B +{ + map m; + void f (); +}; + +extern A *ga; + +void B::f () +{ + for (map::iterator iter = m.begin (); iter != m.end (); ++iter) + { + if (ga->empty) + ga->set (iter->second); + } +} + +/* { dg-final { scan-tree-dump-times "loop split on semi-invariant condition at false branch" 1 "lsplit" } } */ diff --git a/gcc/testsuite/gcc.dg/torture/pr55107.c b/gcc/testsuite/gcc.dg/torture/pr55107.c index 2402716be30..d757c041220 100644 --- a/gcc/testsuite/gcc.dg/torture/pr55107.c +++ b/gcc/testsuite/gcc.dg/torture/pr55107.c @@ -1,4 +1,5 @@ /* { dg-do compile } */ +/* { dg-additional-options "-fno-split-loops" } */ typedef unsigned short uint16_t; diff --git a/gcc/testsuite/gcc.dg/tree-ssa/loop-cond-split-1.c b/gcc/testsuite/gcc.dg/tree-ssa/loop-cond-split-1.c new file mode 100644 index 00000000000..feb776e8373 --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/loop-cond-split-1.c @@ -0,0 +1,97 @@ +/* { dg-do compile } */ +/* { dg-options "-O3 -fdump-tree-lsplit-details" } */ + +extern const int step; + +int ga, gb; + +__attribute__((pure)) __attribute__((noinline)) int inc (int i) +{ + return i + step; +} + +extern int do_something (void); + +void test1 (int n) +{ + int i; + + for (i = 0; i < n; i = inc (i)) + { + if (ga) + ga = do_something (); + } +} + +void test2 (int n, int p) +{ + int i; + int v; + + for (i = 0; i < n ; i = inc (i)) + { + if (ga) + { + v = inc (2); + gb += 1; + } + else + { + v = p * p; + gb *= 3; + } + + if (v < 10) + ga = do_something (); + } +} + +void test3 (int n, int p) +{ + int i; + int c = p + 1; + int v; + + for (i = 0; i < n ; i = inc (i)) + { + if (c) + { + v = inc (c); + gb += 1; + } + else + { + v = p * p; + gb *= 3; + } + + if (v < 10) + c = do_something (); + } +} + +void test4 (int n, int p) +{ + int i; + int v; + + for (i = 0; i < n ; i = inc (i)) + { + if (ga) + { + v = inc (2); + if (gb > 16) + v = inc (5); + } + else + { + v = p * p; + gb += 2; + } + + if (v < 10) + ga = do_something (); + } +} + +/* { dg-final { scan-tree-dump-times "loop split on semi-invariant condition at false branch" 3 "lsplit" } } */ diff --git a/gcc/tree-ssa-loop-split.c b/gcc/tree-ssa-loop-split.c index f5f083384bc..6302d044e09 100644 --- a/gcc/tree-ssa-loop-split.c +++ b/gcc/tree-ssa-loop-split.c @@ -32,7 +32,10 @@ along with GCC; see the file COPYING3. If not see #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 "params.h" #include "tree-scalar-evolution.h" #include "gimple-iterator.h" #include "gimple-pretty-print.h" @@ -40,7 +43,9 @@ along with GCC; see the file COPYING3. If not see #include "gimple-fold.h" #include "gimplify-me.h" -/* This file implements loop splitting, i.e. transformation of loops like +/* This file implements two kinds of loop splitting. + + One transformation of loops like: for (i = 0; i < 100; i++) { @@ -487,8 +492,9 @@ compute_new_first_bound (gimple_seq *stmts, class tree_niter_desc *niter, single exit of LOOP. */ static bool -split_loop (class loop *loop1, class tree_niter_desc *niter) +split_loop (class loop *loop1) { + class tree_niter_desc niter; basic_block *bbs; unsigned i; bool changed = false; @@ -496,8 +502,28 @@ split_loop (class loop *loop1, class tree_niter_desc *niter) 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))) @@ -505,8 +531,8 @@ split_loop (class loop *loop1, class tree_niter_desc *niter) /* 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)) + != 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, @@ -575,7 +601,7 @@ split_loop (class loop *loop1, class tree_niter_desc *niter) 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, + 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), @@ -612,6 +638,956 @@ split_loop (class loop *loop1, class tree_niter_desc *niter) 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 memory_stores; + + /* Whether above memory stores vector has been filled. */ + int need_init; + + /* Control dependencies of basic blocks in a loop. */ + auto_vec *> 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 other_stores; + auto_vec 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 (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 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 * +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 *) 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 pdom_worklist; + hash_set pdom_visited; + hash_set *dep_bbs = new hash_set; + + 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 *pred_dep_bbs + = (hash_set *) pred_bb->aux; + + for (hash_set::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 &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 &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; + + 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 | + | | + v | + .------- if (cond) -------. | + | | | + | [ SKIP ] | + | | | + | x_2 = ... | + | | | + '---- T ---->.<---- F ----' | + | | + v | + x_3 = PHI | + | | + '----------------------' + + 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 (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 &stmt_stat) +{ + hash_set *dep_bbs = find_control_dep_blocks (loop, bb); + + if (!dep_bbs) + return true; + + for (hash_set::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 &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 (stmt); + + if (gimple_bb (stmt) == loop->header) + { + 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 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 worklist; + hash_set 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_VALUE (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_VALUE (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 (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 (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 (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 @@ -621,13 +1597,15 @@ tree_ssa_split_loops (void) 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) { - class tree_niter_desc niter; if (loop->aux) { /* If any of our inner loops was split, don't split us, @@ -636,35 +1614,24 @@ tree_ssa_split_loops (void) 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) - && easy_exit_values (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 - && can_duplicate_loop_p (loop)) + if (optimize_loop_for_size_p (loop)) + continue; + + if (split_loop (loop) || split_loop_on_cond (loop)) { - if (split_loop (loop, &niter)) - { - /* Mark our containing loop as having had some split inner - loops. */ - loop_outer (loop)->aux = loop; - changed = true; - } + /* 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; -- 2.30.2