On Tue, Mar 12, 2019 at 7:20 AM Feng Xue OS <f...@os.amperecomputing.com> wrote: > > This patch is composed to implement a loop transformation on one of its > conditional statements, which we call it semi-invariant, in that its > computation is impacted in only one of its branches. > > Suppose a loop as: > > void f (std::map<int, int> m) > { > for (auto it = m.begin (); it != m.end (); ++it) { > /* if (b) is semi-invariant. */ > if (b) { > b = do_something(); /* Has effect on b */ > } else { > /* No effect on b */ > } > statements; /* Also no effect on b */ > } > } > > A transformation, kind of loop split, could be: > > void f (std::map<int, int> m) > { > for (auto it = m.begin (); it != m.end (); ++it) { > if (b) { > b = do_something(); > } else { > ++it; > statements; > break; > } > statements; > } > > for (; it != m.end (); ++it) { > statements; > } > } > > If "statements" contains nothing, the second loop becomes an empty one, which > can be removed. (This part will be given in another patch). And if > "statements" are straight line instructions, we get an opportunity to > vectorize the second loop. In practice, this optimization is found to improve > some real application by %7. > > Since it is just a kind of loop split, the codes are mainly placed in > existing tree-ssa-loop-split module, and is controlled by -fsplit-loop, and > is enabled with -O3.
Note the transform itself is jump-threading with the threading duplicating a whole CFG cycle. I didn't look at the patch details yet since this is suitable for GCC 10 only. Thanks for implementing this. Richard. > Feng > > > diff --git a/gcc/ChangeLog b/gcc/ChangeLog > index 64bf6017d16..a6c2878d652 100644 > --- a/gcc/ChangeLog > +++ b/gcc/ChangeLog > @@ -1,3 +1,23 @@ > +2019-03-12 Feng Xue <f...@os.amperecomputing.com> > + > + PR tree-optimization/89134 > + * doc/invoke.texi (max-cond-loop-split-insns): Document new --params. > + (min-cond-loop-split-prob): Likewise. > + * params.def: Add max-cond-loop-split-insns, min-cond-loop-split-prob. > + * passes.def (pass_cond_loop_split) : New pass. > + * timevar.def (TV_COND_LOOP_SPLIT): New time variable. > + * tree-pass.h (make_pass_cond_loop_split): New declaration. > + * tree-ssa-loop-split.c (split_info): New class. > + (find_vdef_in_loop, vuse_semi_invariant_p): New functions. > + (ssa_semi_invariant_p, stmt_semi_invariant_p): Likewise. > + (can_branch_be_excluded, get_cond_invariant_branch): Likewise. > + (is_cond_in_hidden_loop, compute_added_num_insns): Likewise. > + (can_split_loop_on_cond, mark_cond_to_split_loop): Likewise. > + (split_loop_for_cond, tree_ssa_split_loops_for_cond): Likewise. > + (pass_data_cond_loop_split): New variable. > + (pass_cond_loop_split): New class. > + (make_pass_cond_loop_split): New function. > + > 2019-03-11 Jakub Jelinek <ja...@redhat.com> > > PR middle-end/89655 > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi > index df0883f2fc9..f5e09bd71fd 100644 > --- a/gcc/doc/invoke.texi > +++ b/gcc/doc/invoke.texi > @@ -11316,6 +11316,14 @@ 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 max-cond-loop-split-insns > +The maximum number of insns to be increased due to loop split on > +semi-invariant condition statement. > + > +@item min-cond-loop-split-prob > +The minimum threshold for probability of semi-invaraint 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 3f1576448be..2e067526958 100644 > --- a/gcc/params.def > +++ b/gcc/params.def > @@ -386,6 +386,18 @@ DEFPARAM(PARAM_MAX_UNSWITCH_LEVEL, > "The maximum number of unswitchings in a single loop.", > 3, 0, 0) > > +/* The maximum number of increased insns due to loop split on semi-invariant > + condition statement. */ > +DEFPARAM(PARAM_MAX_COND_LOOP_SPLIT_INSNS, > + "max-cond-loop-split-insns", > + "The maximum number of insns to be increased due to loop split on > semi-invariant condition statement.", > + 100, 0, 0) > + > +DEFPARAM(PARAM_MIN_COND_LOOP_SPLIT_PROB, > + "min-cond-loop-split-prob", > + "The minimum threshold for probability of semi-invaraint 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/passes.def b/gcc/passes.def > index 446a7c48276..bde7f4c50c0 100644 > --- a/gcc/passes.def > +++ b/gcc/passes.def > @@ -265,6 +265,7 @@ along with GCC; see the file COPYING3. If not see > NEXT_PASS (pass_tree_unswitch); > NEXT_PASS (pass_scev_cprop); > NEXT_PASS (pass_loop_split); > + NEXT_PASS (pass_cond_loop_split); > NEXT_PASS (pass_loop_versioning); > NEXT_PASS (pass_loop_jam); > /* All unswitching, final value replacement and splitting can expose > diff --git a/gcc/timevar.def b/gcc/timevar.def > index 54154464a58..39f2df0e3ec 100644 > --- a/gcc/timevar.def > +++ b/gcc/timevar.def > @@ -189,6 +189,7 @@ DEFTIMEVAR (TV_TREE_LOOP_IVCANON , "tree canonical > iv") > DEFTIMEVAR (TV_SCEV_CONST , "scev constant prop") > DEFTIMEVAR (TV_TREE_LOOP_UNSWITCH , "tree loop unswitching") > DEFTIMEVAR (TV_LOOP_SPLIT , "loop splitting") > +DEFTIMEVAR (TV_COND_LOOP_SPLIT , "loop splitting for conditions") > DEFTIMEVAR (TV_LOOP_JAM , "unroll and jam") > DEFTIMEVAR (TV_COMPLETE_UNROLL , "complete unrolling") > DEFTIMEVAR (TV_TREE_PARALLELIZE_LOOPS, "tree parallelize loops") > diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h > index 47be59b2a11..f441ba36871 100644 > --- a/gcc/tree-pass.h > +++ b/gcc/tree-pass.h > @@ -367,6 +367,7 @@ extern gimple_opt_pass *make_pass_lim (gcc::context > *ctxt); > extern gimple_opt_pass *make_pass_linterchange (gcc::context *ctxt); > extern gimple_opt_pass *make_pass_tree_unswitch (gcc::context *ctxt); > extern gimple_opt_pass *make_pass_loop_split (gcc::context *ctxt); > +extern gimple_opt_pass *make_pass_cond_loop_split (gcc::context *ctxt); > extern gimple_opt_pass *make_pass_loop_jam (gcc::context *ctxt); > extern gimple_opt_pass *make_pass_predcom (gcc::context *ctxt); > extern gimple_opt_pass *make_pass_iv_canon (gcc::context *ctxt); > diff --git a/gcc/tree-ssa-loop-split.c b/gcc/tree-ssa-loop-split.c > index 999c9a30366..d287a0d7d4c 100644 > --- a/gcc/tree-ssa-loop-split.c > +++ b/gcc/tree-ssa-loop-split.c > @@ -32,7 +32,9 @@ 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 "cfgloop.h" > +#include "params.h" > #include "tree-scalar-evolution.h" > #include "gimple-iterator.h" > #include "gimple-pretty-print.h" > @@ -40,7 +42,9 @@ 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 kind of loop splitting. > + > + One transformation of loops like: > > for (i = 0; i < 100; i++) > { > @@ -670,6 +674,803 @@ tree_ssa_split_loops (void) > return 0; > } > > + > +/* Another transformation of loops like: > + > + for (i = INIT (); CHECK (i); i = NEXT ()) > + { > + if (expr (a_1, a_2, ..., a_n)) > + 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 *> stores; > + > + /* Whether above memory stores vector has been filled. */ > + bool set_stores; > + > + /* Semi-invariant conditional statement, upon which to split loop. */ > + gcond *cond; > + > + split_info () : bbs (NULL), set_stores (false), cond (NULL) { } > + > + ~split_info () > + { > + if (bbs) > + free (bbs); > + } > +}; > + > +/* Find all statements with memory-write effect in a loop, including memory > + store and non-pure function call, and keep those in a vector. This work > + is only done for 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->set_stores = true; > + > + /* 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 *> others; > + 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 toward the > + first, which ensure that this do-while will not touch SSA names > + defined outside of 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 the idea of of using them as > + shortcut terminators to memory alias analysis, kind of > + optimization for compilation. */ > + if (gimple_code (stmt) == GIMPLE_CALL) > + info->stores.safe_push (stmt); > + else > + others.safe_push (stmt); > + > + if (bitmap_set_bit (visited, SSA_NAME_VERSION (prev))) > + worklist.safe_push (prev); > + } > + } while (!worklist.is_empty ()); > + > + info->stores.safe_splice (others); > +} > + > + > +/* Given a memory load or pure call statement, check whether it is impacted > + by some memory store in the loop excluding those basic blocks dominated > + by SKIP_HEAD (those basic blocks always corresponds to one branch of > + a conditional statement). If SKIP_HEAD is NULL, all basic blocks of the > + 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; > + > + /* Collect memory store/clobber statements if have not do that. */ > + if (!info->set_stores) > + find_vdef_in_loop (loop); > + > + tree rhs = is_gimple_assign (stmt) ? gimple_assign_rhs1 (stmt) : NULL_TREE; > + ao_ref ref; > + gimple *store; > + unsigned i; > + > + ao_ref_init (&ref, rhs); > + > + FOR_EACH_VEC_ELT (info->stores, i, store) > + { > + /* Skip those basic blocks dominated by SKIP_HEAD. */ > + if (skip_head > + && dominated_by_p (CDI_DOMINATORS, gimple_bb (store), skip_head)) > + continue; > + > + /* For a pure call, it is assumed to be impacted by any memory store. > + For a memory load, use memory alias analysis to check that. */ > + if (!ref.ref || stmt_may_clobber_ref_p_1 (store, &ref)) > + return false; > + } > + > + return true; > +} > + > +/* Forward declaration */ > + > +static bool > +stmt_semi_invariant_p (struct loop *loop, gimple *stmt, > + const_basic_block skip_head); > + > +/* Suppose one condition branch, led by SKIP_HEAD, is not executed in certain > + iteration, check whether an SSA name remains unchanged in next interation. > + We can call this characterisic as semi-invariantness. SKIP_HEAD might be > + NULL, if so, nothing excluded, all basic blocks and control flows in the > + loop will be considered. */ > + > +static bool > +ssa_semi_invariant_p (struct loop *loop, const tree name, > + const_basic_block skip_head) > +{ > + gimple *def = SSA_NAME_DEF_STMT (name); > + const_basic_block def_bb = gimple_bb (def); > + > + /* An SSA name defined outside a loop is definitely semi-invariant. */ > + if (!def_bb || !flow_bb_inside_loop_p (loop, def_bb)) > + return true; > + > + /* This function is used to check semi-invariantness of a condition > + statement, and SKIP_HEAD is always given as head of one of its > + branches. So it implies that SSA name to check should be defined > + before the conditional statement, and also before SKIP_HEAD. */ > + > + if (gimple_code (def) == GIMPLE_PHI) > + { > + /* In a normal loop, if a PHI node is located not in loop header, all > + its source operands should be defined inside the loop. As we > + mentioned before, these source definitions are ahead of SKIP_HEAD, > + and will not be bypassed. Therefore, in each iteration, any of > + these sources might be value provider to the SSA name, which for > + sure should not be seen as invariant. */ > + if (def_bb != loop->header || !skip_head) > + return false; > + > + const_edge latch = loop_latch_edge (loop); > + tree from = PHI_ARG_DEF_FROM_EDGE (as_a <gphi *> (def), latch); > + > + /* A PHI node in loop header always contains two source operands, > + one is initial value, the other is the copy of last iteration > + through loop latch, we call it latch value. From this PHI node > + to definition of latch value, if excluding those basic blocks > + dominated by SKIP_HEAD, there is no definition of other version > + of same variable, 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 (x2) 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 of 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) > + { > + const_edge e = gimple_phi_arg_edge (phi, i); > + > + /* Skip redefinition from basic blocks being excluded. */ > + if (!dominated_by_p (CDI_DOMINATORS, e->src, skip_head)) > + { > + /* There are more than one source operands that can > + provide value to the SSA name. */ > + if (from) > + return false; > + > + from = gimple_phi_arg_def (phi, i); > + } > + } > + } > + 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; > + } > + > + /* Value originated from volatile memory load or return of normal (non- > + const/pure) call should not be treated as constant in each iteration. */ > + if (gimple_has_side_effects (def)) > + return false; > + > + /* Check if any memory store may kill memory load at this place. */ > + if (gimple_vuse (def) && !vuse_semi_invariant_p (loop, def, skip_head)) > + return false; > + > + /* Check operands of definition statement of the SSA name. */ > + return stmt_semi_invariant_p (loop, def, skip_head); > +} > + > +/* Check whether a statement is semi-invariant, iff all its operands are > + semi-invariant. */ > + > +static bool > +stmt_semi_invariant_p (struct loop *loop, gimple *stmt, > + const_basic_block skip_head) > +{ > + ssa_op_iter iter; > + tree use; > + > + /* Although operand of a statement might be SSA name, CONSTANT or VARDECL, > + here we only need to check SSA name operands. For VARDECL operand > + involves memory load, check on VARDECL operand must have been done > + prior to invocation of this function in ssa_semi_invariant_p. */ > + FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE) > + { > + if (!ssa_semi_invariant_p (loop, use, skip_head)) > + return false; > + } > + > + return true; > +} > + > +/* Determine if unselect one branch of a conditional statement, whether we > + can exclude leading basic block of the branch and those basic blocks > + dominated by the leading one. */ > + > +static bool > +can_branch_be_excluded (basic_block branch_bb) > +{ > + if (single_pred_p (branch_bb)) > + return true; > + > + edge e; > + edge_iterator ei; > + > + 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 through other path, not just from the > + conditional statement. */ > + return false; > + } > + > + return true; > +} > + > +/* Find out which branch of a conditional statement is invariant. That > + is: once the branch is selected in certain loop iteration, any operand > + that contributes to computation of the conditional statement remains > + unchanged in all following iterations. */ > + > +static int > +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; > + > + 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 loop-breaking. > + 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 -1; > + } > + > + invar_checks = 0; > + > + for (unsigned i = 0; i < 2; i++) > + { > + invar[!i] = false; > + > + if (!can_branch_be_excluded (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 -1; > + > + /* Found a real loop-invariant condition, do nothing. */ > + if (invar_checks < 2 && stmt_semi_invariant_p (loop, cond, NULL)) > + return -1; > + > + return invar[1]; > +} > + > +/* Return TRUE is conditional statement in a normal loop is also inside > + a nested non-recognized loop, such as an irreducible loop. */ > + > +static bool > +is_cond_in_hidden_loop (const struct loop *loop, basic_block cond_bb, > + int branch) > +{ > + basic_block branch_bb = EDGE_SUCC (cond_bb, branch)->dest; > + > + if (cond_bb == loop->header || branch_bb == loop->latch) > + return false; > + > + basic_block *bbs = ((split_info *) loop->aux)->bbs; > + auto_vec<basic_block> worklist; > + > + for (unsigned i = 0; i < loop->num_nodes; i++) > + bbs[i]->flags &= ~BB_REACHABLE; > + > + /* Mark latch basic block as visited to be end point for reachablility > + traversal. */ > + loop->latch->flags |= BB_REACHABLE; > + > + gcc_assert (flow_bb_inside_loop_p (loop, branch_bb)); > + > + /* Start from specified branch, the opposite branch is ignored for it > + will not be executed. */ > + branch_bb->flags |= BB_REACHABLE; > + worklist.safe_push (branch_bb); > + > + do > + { > + basic_block bb = worklist.pop (); > + edge e; > + edge_iterator ei; > + > + FOR_EACH_EDGE (e, ei, bb->succs) > + { > + basic_block succ_bb = e->dest; > + > + if (succ_bb == cond_bb) > + return true; > + > + if (!flow_bb_inside_loop_p (loop, succ_bb)) > + continue; > + > + if (succ_bb->flags & BB_REACHABLE) > + continue; > + > + succ_bb->flags |= BB_REACHABLE; > + worklist.safe_push (succ_bb); > + } > + } while (!worklist.is_empty ()); > + > + return false; > +} > + > + > +/* Calculate increased code size measured by estimated insn number if > + applying loop split upon certain branch of a conditional statement. */ > + > +static int > +compute_added_num_insns (struct loop *loop, const_basic_block cond_bb, > + int branch) > +{ > + const_basic_block targ_bb_var = 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], targ_bb_var)) > + continue; > + > + for (gimple_stmt_iterator gsi = gsi_start_bb (bbs[i]); !gsi_end_p > (gsi); > + gsi_next (&gsi)) > + num += estimate_num_insns (gsi_stmt (gsi), &eni_size_weights); > + } > + > + return num; > +} > + > +/* Return true if it is eligible and profitable to perform loop split upon > + a conditional statement. */ > + > +static bool > +can_split_loop_on_cond (struct loop *loop, gcond *cond) > +{ > + int branch = get_cond_invariant_branch (loop, cond); > + > + if (branch < 0) > + return false; > + > + basic_block cond_bb = gimple_bb (cond); > + > + /* Add a threshold for increased code size to disable loop split. */ > + if (compute_added_num_insns (loop, cond_bb, branch) > > + PARAM_VALUE (PARAM_MAX_COND_LOOP_SPLIT_INSNS)) > + return false; > + > + /* In each interation, conditional statement candidate should be > + executed only once. */ > + if (is_cond_in_hidden_loop (loop, cond_bb, branch)) > + return false; > + > + profile_probability prob = EDGE_SUCC (cond_bb, branch)->probability; > + > + /* When accurate profile information is available, and execution > + frequency of the branch is too low, just let it go. */ > + if (prob.reliable_p ()) > + { > + int thres = PARAM_VALUE (PARAM_MIN_COND_LOOP_SPLIT_PROB); > + > + if (prob < profile_probability::always ().apply_scale (thres, 100)) > + return false; > + } > + > + /* Temporarily keep branch index in conditional statement. */ > + gimple_set_plf (cond, GF_PLF_1, branch); > + return true; > +} > + > +/* Traverse all conditional statements in a loop, to find out a good > + candidate upon which we can do loop split. */ > + > +static bool > +mark_cond_to_split_loop (struct loop *loop) > +{ > + split_info *info = new split_info (); > + basic_block *bbs = info->bbs = get_loop_body (loop); > + > + /* 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++) > + { > + basic_block bb = bbs[i]; > + > + /* Skip statement in inner recognized loop, because we want that > + conditional statement executes at most once in each iteration. */ > + if (bb->loop_father != loop) > + continue; > + > + /* Actually this check is not a must constraint. With it, we can > + ensure conditional statement will execute at least once 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); > + > + if (can_split_loop_on_cond (loop, cond)) > + { > + info->cond = cond; > + return true; > + } > + } > + > + delete info; > + loop->aux = NULL; > + > + return false; > +} > + > +/* Given a loop with a chosen conditional statement candidate, perform loop > + split transformation illustrated as the following graph. > + > + .-------T------ if (true) ------F------. > + | .---------------. | > + | | | | > + v | v v > + pre-header | pre-header > + | .------------. | | .------------. > + | | | | | | | > + | v | | | v | > + header | | header | > + | | | | | > + [ bool r = cond; ] | | | | > + | | | | | > + .---- if (r) -----. | | .--- if (true) ---. | > + | | | | | | | > + invariant | | | invariant | | > + | | | | | | | > + '---T--->.<---F---' | | '---T--->.<---F---' | > + | | / | | > + stmts | / stmts | > + | | / | | > + / \ | / / \ | > + .-------* * [ if (!r) ] .-------* * | > + | | | | | | > + | 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 loop1, a new bool temporary (r) > + is introduced to keep value of the condition result. In original latch > + edge of loop1, we insert a new conditional statement whose value comes > + from previous temporary (r), 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 candidate by setting a constant bool condition, > + based on which branch is semi-invariant. */ > + > +static bool > +split_loop_for_cond (struct loop *loop1) > +{ > + split_info *info = (split_info *) loop1->aux; > + gcond *cond = info->cond; > + basic_block cond_bb = gimple_bb (cond); > + int branch = gimple_plf (cond, GF_PLF_1); > + bool true_invar = !!(EDGE_SUCC (cond_bb, branch)->flags & EDGE_TRUE_VALUE); > + > + if (dump_file && (dump_flags & TDF_DETAILS)) > + { > + fprintf (dump_file, "In %s(), split loop %d at branch<%s>, BB %d\n", > + current_function_name (), loop1->num, > + true_invar ? "T" : "F", cond_bb->index); > + print_gimple_stmt (dump_file, cond, 0, TDF_SLIM | TDF_VOPS); > + } > + > + 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; > + } > + > + /* Generate a bool type temporary to hold result of the condition. */ > + tree tmp = make_ssa_name (boolean_type_node); > + gimple_stmt_iterator gsi = gsi_last_bb (cond_bb); > + gimple *stmt = gimple_build_assign (tmp, > + gimple_cond_code (cond), > + gimple_cond_lhs (cond), > + gimple_cond_rhs (cond)); > + > + gsi_insert_before (&gsi, stmt, GSI_NEW_STMT); > + gimple_cond_set_condition (cond, EQ_EXPR, tmp, boolean_true_node); > + update_stmt (cond); > + > + /* Replace the condition in loop2 with a bool constant to let pass > + manager remove the variant branch after current pass finishes. */ > + basic_block cond_bb_copy = get_bb_copy (cond_bb); > + gcond *cond_copy = as_a<gcond *> (last_stmt (cond_bb_copy)); > + > + 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. 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 (EQ_EXPR, tmp, boolean_true_node, > + NULL_TREE, NULL_TREE); > + > + 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; > + > + if (true_invar) > + { > + to_loop1->flags |= EDGE_FALSE_VALUE; > + to_loop2->flags |= EDGE_TRUE_VALUE; > + } > + else > + { > + to_loop1->flags |= EDGE_TRUE_VALUE; > + to_loop2->flags |= 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; > +} > + > +/* Main entry point to perform loop splitting for suitable if-conditions > + in all loops. */ > + > +static unsigned int > +tree_ssa_split_loops_for_cond (void) > +{ > + struct loop *loop; > + auto_vec<struct loop *> loop_list; > + bool changed = false; > + unsigned i; > + > + FOR_EACH_LOOP (loop, LI_INCLUDE_ROOT) > + loop->aux = NULL; > + > + /* Go through all loops starting from innermost. */ > + FOR_EACH_LOOP (loop, LI_FROM_INNERMOST) > + { > + /* Put loop in a list if found a conditional statement candidate in > + the loop. This is stage for analysis, no change anything in the > + function. */ > + if (!loop->aux > + && !optimize_loop_for_size_p (loop) > + && mark_cond_to_split_loop (loop)) > + loop_list.safe_push (loop); > + > + /* 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->aux; > + } > + > + FOR_EACH_VEC_ELT (loop_list, i, loop) > + { > + /* Extract selected loop and perform loop split. This is stage for > + transformation. */ > + changed |= split_loop_for_cond (loop); > + > + delete (split_info *) loop->aux; > + } > + > + FOR_EACH_LOOP (loop, LI_INCLUDE_ROOT) > + loop->aux = NULL; > + > + if (changed) > + return TODO_cleanup_cfg; > + return 0; > +} > + > + > /* Loop splitting pass. */ > > namespace { > @@ -716,3 +1517,48 @@ make_pass_loop_split (gcc::context *ctxt) > { > return new pass_loop_split (ctxt); > } > + > +namespace { > + > +const pass_data pass_data_cond_loop_split = > +{ > + GIMPLE_PASS, /* type */ > + "cond_lsplit", /* name */ > + OPTGROUP_LOOP, /* optinfo_flags */ > + TV_COND_LOOP_SPLIT, /* tv_id */ > + PROP_cfg, /* properties_required */ > + 0, /* properties_provided */ > + 0, /* properties_destroyed */ > + 0, /* todo_flags_start */ > + 0, /* todo_flags_finish */ > +}; > + > +class pass_cond_loop_split : public gimple_opt_pass > +{ > +public: > + pass_cond_loop_split (gcc::context *ctxt) > + : gimple_opt_pass (pass_data_cond_loop_split, ctxt) > + {} > + > + /* opt_pass methods: */ > + virtual bool gate (function *) { return flag_split_loops != 0; } > + virtual unsigned int execute (function *); > + > +}; // class pass_cond_loop_split > + > +unsigned int > +pass_cond_loop_split::execute (function *fun) > +{ > + if (number_of_loops (fun) <= 1) > + return 0; > + > + return tree_ssa_split_loops_for_cond (); > +} > + > +} // anon namespace > + > +gimple_opt_pass * > +make_pass_cond_loop_split (gcc::context *ctxt) > +{ > + return new pass_cond_loop_split (ctxt); > +}