On Wed, Mar 13, 2019 at 10:40 AM Kyrill Tkachov
<kyrylo.tkac...@foss.arm.com> wrote:
>
> Hi Feng,
>
> On 3/13/19 1:56 AM, Feng Xue OS wrote:
> > 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?
> >
> >
>
> GCC 10 will be released once the number of P1 regressions gets down to
> zero. Past experience shows that it's around the April/May timeframe.
Note GCC 10 is due only next year.
> In the meantime my comment on the patch is that you should add some
> tests to the testsuite that showcase this transformation.
>
> Thanks,
>
> Kyrill
>
>
> > 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);
> > > +}
