Richard,
Thanks for your comment. Yes, it is like kind of jump threading with
knowledge of loop structure. And what is rough time for GCC 10?
Regards,
Feng
________________________________
From: Richard Biener <richard.guent...@gmail.com>
Sent: Tuesday, March 12, 2019 4:31:49 PM
To: Feng Xue OS
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] Loop split upon semi-invariant condition (PR
tree-optimization/89134)
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);
> +}
