---
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 1391a562c35..28981fa1048 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -11418,6 +11418,19 @@ 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
+In a loop, if a branch of a conditional statement is selected since certain
+loop iteration, any operand that contributes to computation of the conditional
+expression remains unchanged in all following iterations, the statement is
+semi-invariant, upon which we can do a kind of loop split transformation.
+@option{max-cond-loop-split-insns} controls maximum number of insns to be
+added due to loop split on semi-invariant conditional statement.
+
+@item min-cond-loop-split-prob
+When FDO profile information is available, @option{min-cond-loop-split-prob}
+specifies minimum threshold for probability of semi-invariant condition
+statement to trigger loop split.
+
@item iv-consider-all-candidates-bound
Bound on number of candidates for induction variables, below which
all candidates are considered for each use in induction variable
diff --git a/gcc/params.def b/gcc/params.def
index 13001a7bb2d..12bc8c26c9e 100644
--- a/gcc/params.def
+++ b/gcc/params.def
@@ -386,6 +386,20 @@ 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 added 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-invariant condition "
+ "statement to trigger loop split.",
+ 30, 0, 100)
+
/* The maximum number of insns in loop header duplicated by the copy loop
headers pass. */
DEFPARAM(PARAM_MAX_LOOP_HEADER_INSNS,
diff --git a/gcc/testsuite/g++.dg/tree-ssa/loop-cond-split-1.C
b/gcc/testsuite/g++.dg/tree-ssa/loop-cond-split-1.C
new file mode 100644
index 00000000000..51f9da22fc7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/loop-cond-split-1.C
@@ -0,0 +1,33 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-lsplit-details" } */
+
+#include <string>
+#include <map>
+
+using namespace std;
+
+class A
+{
+public:
+ bool empty;
+ void set (string s);
+};
+
+class B
+{
+ map<int, string> m;
+ void f ();
+};
+
+extern A *ga;
+
+void B::f ()
+{
+ for (map<int, string>::iterator iter = m.begin (); iter != m.end (); ++iter)
+ {
+ if (ga->empty)
+ ga->set (iter->second);
+ }
+}
+
+/* { dg-final { scan-tree-dump-times "split loop 1 at branch" 1 "lsplit" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/loop-cond-split-1.c
b/gcc/testsuite/gcc.dg/tree-ssa/loop-cond-split-1.c
new file mode 100644
index 00000000000..bbd522d6bcd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/loop-cond-split-1.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-lsplit-details" } */
+
+__attribute__((pure)) __attribute__((noinline)) int inc (int i)
+{
+ return i + 1;
+}
+
+extern int do_something (void);
+extern int b;
+
+void test(int n)
+{
+ int i;
+
+ for (i = 0; i < n; i = inc (i))
+ {
+ if (b)
+ b = do_something();
+ }
+}
+
+/* { dg-final { scan-tree-dump-times "split loop 1 at branch" 1 "lsplit" } } */
diff --git a/gcc/tree-ssa-loop-split.c b/gcc/tree-ssa-loop-split.c
index f5f083384bc..e4a1b6d2019 100644
--- a/gcc/tree-ssa-loop-split.c
+++ b/gcc/tree-ssa-loop-split.c
@@ -32,7 +32,10 @@ along with GCC; see the file COPYING3. If not see
#include "tree-ssa-loop.h"
#include "tree-ssa-loop-manip.h"
#include "tree-into-ssa.h"
+#include "tree-inline.h"
+#include "tree-cfgcleanup.h"
#include "cfgloop.h"
+#include "params.h"
#include "tree-scalar-evolution.h"
#include "gimple-iterator.h"
#include "gimple-pretty-print.h"
@@ -40,7 +43,9 @@ along with GCC; see the file COPYING3. If not see
#include "gimple-fold.h"
#include "gimplify-me.h"
-/* This file implements loop splitting, i.e. transformation of loops like
+/* This file implements two kinds of loop splitting.
+
+ One transformation of loops like:
for (i = 0; i < 100; i++)
{
@@ -612,6 +617,722 @@ split_loop (class loop *loop1, class tree_niter_desc
*niter)
return changed;
}
+/* Another transformation of loops like:
+
+ for (i = INIT (); CHECK (i); i = NEXT ())
+ {
+ if (expr (a_1, a_2, ..., a_n)) // expr is pure
+ a_j = ...; // change at least one a_j
+ else
+ S; // not change any a_j
+ }
+
+ into:
+
+ for (i = INIT (); CHECK (i); i = NEXT ())
+ {
+ if (expr (a_1, a_2, ..., a_n))
+ a_j = ...;
+ else
+ {
+ S;
+ i = NEXT ();
+ break;
+ }
+ }
+
+ for (; CHECK (i); i = NEXT ())
+ {
+ S;
+ }
+
+ */
+
+/* Data structure to hold temporary information during loop split upon
+ semi-invariant conditional statement. */
+class split_info {
+public:
+ /* Array of all basic blocks in a loop, returned by get_loop_body(). */
+ basic_block *bbs;
+
+ /* All memory store/clobber statements in a loop. */
+ auto_vec<gimple *> memory_stores;
+
+ /* Whether above memory stores vector has been filled. */
+ int need_init;
+
+ split_info () : bbs (NULL), need_init (true) { }
+
+ ~split_info ()
+ {
+ if (bbs)
+ free (bbs);
+ }
+};
+
+/* Find all statements with memory-write effect in LOOP, including memory
+ store and non-pure function call, and keep those in a vector. This work
+ is only done one time, for the vector should be constant during analysis
+ stage of semi-invariant condition. */
+
+static void
+find_vdef_in_loop (struct loop *loop)
+{
+ split_info *info = (split_info *) loop->aux;
+ gphi *vphi = get_virtual_phi (loop->header);
+
+ /* Indicate memory store vector has been filled. */
+ info->need_init = false;
+
+ /* If loop contains memory operation, there must be a virtual PHI node in
+ loop header basic block. */
+ if (vphi == NULL)
+ return;
+
+ /* All virtual SSA names inside the loop are connected to be a cyclic
+ graph via virtual PHI nodes. The virtual PHI node in loop header just
+ links the first and the last virtual SSA names, by using the last as
+ PHI operand to define the first. */
+ const edge latch = loop_latch_edge (loop);
+ const tree first = gimple_phi_result (vphi);
+ const tree last = PHI_ARG_DEF_FROM_EDGE (vphi, latch);
+
+ /* The virtual SSA cyclic graph might consist of only one SSA name, who
+ is defined by itself.
+
+ .MEM_1 = PHI <.MEM_2(loop entry edge), .MEM_1(latch edge)>
+
+ This means the loop contains only memory loads, so we can skip it. */
+ if (first == last)
+ return;
+
+ auto_vec<gimple *> other_stores;
+ auto_vec<tree> worklist;
+ auto_bitmap visited;
+
+ bitmap_set_bit (visited, SSA_NAME_VERSION (first));
+ bitmap_set_bit (visited, SSA_NAME_VERSION (last));
+ worklist.safe_push (last);
+
+ do
+ {
+ tree vuse = worklist.pop ();
+ gimple *stmt = SSA_NAME_DEF_STMT (vuse);
+
+ /* We mark the first and last SSA names as visited at the beginning,
+ and reversely start the process from the last SSA name towards the
+ first, which ensures that this do-while will not touch SSA names
+ defined outside 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 an idea of of using them as shortcut
+ terminators to memory alias analysis. */
+ if (gimple_code (stmt) == GIMPLE_CALL)
+ info->memory_stores.safe_push (stmt);
+ else
+ other_stores.safe_push (stmt);
+
+ if (bitmap_set_bit (visited, SSA_NAME_VERSION (prev)))
+ worklist.safe_push (prev);
+ }
+ } while (!worklist.is_empty ());
+
+ info->memory_stores.safe_splice (other_stores);
+}
+
+
+/* Given STMT, memory load or pure call statement, check whether it is impacted
+ by some memory store in LOOP, excluding trace starting from SKIP_HEAD (the
+ trace is composed of SKIP_HEAD and those basic block dominated by it, always
+ corresponds to one branch of a conditional statement). If SKIP_HEAD is
+ NULL, all basic blocks of LOOP are checked. */
+
+static bool
+vuse_semi_invariant_p (struct loop *loop, gimple *stmt,
+ const_basic_block skip_head)
+{
+ split_info *info = (split_info *) loop->aux;
+
+ /* Collect memory store/clobber statements if have not do that. */
+ if (info->need_init)
+ 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->memory_stores, i, store)
+ {
+ /* Skip basic blocks dominated by SKIP_HEAD, if non-NULL. */
+ if (skip_head
+ && dominated_by_p (CDI_DOMINATORS, gimple_bb (store), skip_head))
+ continue;
+
+ if (!ref.ref || stmt_may_clobber_ref_p_1 (store, &ref))
+ return false;
+ }
+
+ return true;
+}
+
+/* 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 since
+ certain iteration of LOOP, check whether an SSA name (NAME) remains
+ unchanged in next interation. We 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. If non-
+ NULL, SSA name to check is supposed to be defined before SKIP_HEAD. */
+
+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;
+
+ if (gimple_code (def) == GIMPLE_PHI)
+ {
+ /* For PHI node that is not in loop header, its source operands should
+ be defined inside the loop, which are seen as loop variant. */
+ 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 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 the PHI node to definition
+ of latch value, if excluding branch trace from 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);
+
+ /* Not consider redefinitions in excluded basic blocks. */
+ 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, it is variant. */
+ 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 STMT is semi-invariant in LOOP, iff all its operands are
+ semi-invariant. Trace composed of basic block SKIP_HEAD and basic blocks
+ dominated by it are excluded from the loop. */
+
+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. This is because check on
+ VARDECL operands, which involve memory loads, must have been done
+ prior to invocation of this function in vuse_semi_invariant_p. */
+ FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
+ {
+ if (!ssa_semi_invariant_p (loop, use, skip_head))
+ return false;
+ }
+
+ return true;
+}
+
+/* Determine when conditional statement never transfers execution to one of its
+ branch, whether we can remove the branch's leading basic block (BRANCH_BB)
+ and those basic blocks dominated by BRANCH_BB. */
+
+static bool
+branch_removable_p (basic_block branch_bb)
+{
+ 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 from opposite branch, or from some
+ statement not dominated by the conditional statement. */
+ return false;
+ }
+
+ return true;
+}
+
+/* Find out which branch of a conditional statement (COND) is invariant in the
+ execution context of LOOP. That is: once the branch is selected in certain
+ iteration of the loop, any operand that contributes to computation of the
+ conditional statement remains unchanged in all following iterations. */
+
+static edge
+get_cond_invariant_branch (struct loop *loop, gcond *cond)
+{
+ basic_block cond_bb = gimple_bb (cond);
+ basic_block targ_bb[2];
+ bool invar[2];
+ unsigned invar_checks;
+
+ for (unsigned i = 0; i < 2; i++)
+ {
+ targ_bb[i] = EDGE_SUCC (cond_bb, i)->dest;
+
+ /* One branch directs to loop exit, no need to perform loop split upon
+ this conditional statement. Firstly, it is trivial if the exit branch
+ is semi-invariant, for the statement is just to break loop. Secondly,
+ if the opposite branch is semi-invariant, it means that the statement
+ is real loop-invariant, which is covered by loop unswitch. */
+ if (!flow_bb_inside_loop_p (loop, targ_bb[i]))
+ return NULL;
+ }
+
+ invar_checks = 0;
+
+ for (unsigned i = 0; i < 2; i++)
+ {
+ invar[!i] = false;
+
+ if (!branch_removable_p (targ_bb[i]))
+ continue;
+
+ /* Given a semi-invariant branch, if its opposite branch dominates
+ loop latch, it and its following trace will only be executed in
+ final iteration of loop, namely it is not part of repeated body
+ of the loop. Similar to the above case that the branch is loop
+ exit, no need to split loop. */
+ if (dominated_by_p (CDI_DOMINATORS, loop->latch, targ_bb[i]))
+ continue;
+
+ invar[!i] = stmt_semi_invariant_p (loop, cond, targ_bb[i]);
+ invar_checks++;
+ }
+
+ /* With both branches being invariant (handled by loop unswitch) or
+ variant is not what we want. */
+ if (invar[0] ^ !invar[1])
+ return NULL;
+
+ /* Found a real loop-invariant condition, do nothing. */
+ if (invar_checks < 2 && stmt_semi_invariant_p (loop, cond, NULL))
+ return NULL;
+
+ return EDGE_SUCC (cond_bb, (unsigned) invar[1]);
+}
+
+/* Calculate increased code size measured by estimated insn number if applying
+ loop split upon certain branch (BRANCH_EDGE) of a conditional statement. */
+
+static int
+compute_added_num_insns (struct loop *loop, const_edge branch_edge)
+{
+ basic_block cond_bb = branch_edge->src;
+ unsigned branch = EDGE_SUCC (cond_bb, 1) == branch_edge;
+ basic_block opposite_bb = EDGE_SUCC (cond_bb, !branch)->dest;
+ basic_block *bbs = ((split_info *) loop->aux)->bbs;
+ int num = 0;
+
+ for (unsigned i = 0; i < loop->num_nodes; i++)
+ {
+ /* Do no count basic blocks only in opposite branch. */
+ if (dominated_by_p (CDI_DOMINATORS, bbs[i], opposite_bb))
+ continue;
+
+ num += estimate_num_insns_seq (bb_seq (bbs[i]), &eni_size_weights);
+ }
+
+ /* It is unnecessary to evaluate expression of the conditional statement
+ in new loop that contains only invariant branch. This expresion should
+ be constant value (either true or false). Exclude code size of insns
+ that contribute to computation of the expression. */
+
+ auto_vec<gimple *> worklist;
+ hash_set<gimple *> removed;
+ gimple *stmt = last_stmt (cond_bb);
+
+ worklist.safe_push (stmt);
+ removed.add (stmt);
+ num -= estimate_num_insns (stmt, &eni_size_weights);
+
+ do
+ {
+ ssa_op_iter opnd_iter;
+ use_operand_p opnd_p;
+
+ stmt = worklist.pop ();
+ FOR_EACH_PHI_OR_STMT_USE (opnd_p, stmt, opnd_iter, SSA_OP_USE)
+ {
+ tree opnd = USE_FROM_PTR (opnd_p);
+
+ if (TREE_CODE (opnd) != SSA_NAME || SSA_NAME_IS_DEFAULT_DEF (opnd))
+ continue;
+
+ gimple *opnd_stmt = SSA_NAME_DEF_STMT (opnd);
+ use_operand_p use_p;
+ imm_use_iterator use_iter;
+
+ if (removed.contains (opnd_stmt)
+ || !flow_bb_inside_loop_p (loop, gimple_bb (opnd_stmt)))
+ continue;
+
+ FOR_EACH_IMM_USE_FAST (use_p, use_iter, opnd)
+ {
+ gimple *use_stmt = USE_STMT (use_p);
+
+ if (!is_gimple_debug (use_stmt) && !removed.contains (use_stmt))
+ {
+ opnd_stmt = NULL;
+ break;
+ }
+ }
+
+ if (opnd_stmt)
+ {
+ worklist.safe_push (opnd_stmt);
+ removed.add (opnd_stmt);
+ num -= estimate_num_insns (opnd_stmt, &eni_size_weights);
+ }
+ }
+ } while (!worklist.is_empty ());
+
+ gcc_assert (num >= 0);
+ return num;
+}
+
+/* Find out loop-invariant branch of a conditional statement (COND) if it has,
+ and check whether it is eligible and profitable to perform loop split upon
+ this branch in LOOP. */
+
+static edge
+get_cond_branch_to_split_loop (struct loop *loop, gcond *cond)
+{
+ edge invar_branch = get_cond_invariant_branch (loop, cond);
+
+ if (!invar_branch)
+ return NULL;
+
+ profile_probability prob = invar_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 NULL;
+ }
+
+ /* Add a threshold for increased code size to disable loop split. */
+ if (compute_added_num_insns (loop, invar_branch)
+ > PARAM_VALUE (PARAM_MAX_COND_LOOP_SPLIT_INSNS))
+ return NULL;
+
+ return invar_branch;
+}
+
+/* Given a loop (LOOP1) with a loop-invariant branch (INVAR_BRANCH) of some
+ conditional statement, perform loop split transformation illustrated
+ as the following graph.
+
+ .-------T------ if (true) ------F------.
+ | .---------------. |
+ | | | |
+ v | v v
+ pre-header | pre-header
+ | .------------. | | .------------.
+ | | | | | | |
+ | v | | | v |
+ header | | header |
+ | | | | |
+ [ 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
+do_split_loop_on_cond (struct loop *loop1, edge invar_branch)
+{
+ basic_block cond_bb = invar_branch->src;
+ bool true_invar = !!(invar_branch->flags & EDGE_TRUE_VALUE);
+ gcond *cond = as_a <gcond *> (last_stmt (cond_bb));
+
+ gcc_assert (cond_bb->loop_father == loop1);
+
+ if (dump_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);
+
+ basic_block cond_bb_copy = get_bb_copy (cond_bb);
+ gcond *cond_copy = as_a<gcond *> (last_stmt (cond_bb_copy));
+
+ /* Replace the condition in loop2 with a bool constant to let PassManager
+ remove the variant branch after current pass completes. */
+ if (true_invar)
+ gimple_cond_make_true (cond_copy);
+ else
+ gimple_cond_make_false (cond_copy);
+
+ update_stmt (cond_copy);
+
+ /* Insert a new conditional statement on latch edge of loop1. 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;
+ to_loop1->flags |= true_invar ? EDGE_FALSE_VALUE : EDGE_TRUE_VALUE;
+ to_loop2->flags |= true_invar ? EDGE_TRUE_VALUE : EDGE_FALSE_VALUE;
+
+ update_ssa (TODO_update_ssa);
+
+ /* Due to introduction of a control flow edge from loop1 latch to loop2
+ pre-header, we should update PHIs in loop2 to reflect this connection
+ between loop1 and loop2. */
+ connect_loop_phis (loop1, loop2, to_loop2);
+
+ free_original_copy_tables ();
+
+ rewrite_into_loop_closed_ssa_1 (NULL, 0, SSA_OP_USE, loop1);
+
+ return true;
+}
+
+/* Traverse all conditional statements in LOOP, to find out a good candidate
+ upon which we can do loop split. */
+
+static bool
+split_loop_on_cond (struct loop *loop)
+{
+ split_info *info = new split_info ();
+ basic_block *bbs = info->bbs = get_loop_body (loop);
+ bool do_split = false;
+
+ /* Allocate an area to keep temporary info, and associate its address
+ with loop aux field. */
+ loop->aux = info;
+
+ for (unsigned i = 0; i < loop->num_nodes; i++)
+ {
+ basic_block bb = bbs[i];
+
+ /* We only consider conditional statement, which be executed at most once
+ in each iteration of the loop. So skip statements in inner loops. */
+ if ((bb->loop_father != loop) || (bb->flags & BB_IRREDUCIBLE_LOOP))
+ continue;
+
+ /* Actually this check is not a must constraint. With it, we can ensure
+ conditional statement will always be executed in each iteration. */
+ if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb))
+ continue;
+
+ gimple *last = last_stmt (bb);
+
+ if (!last || gimple_code (last) != GIMPLE_COND)
+ continue;
+
+ gcond *cond = as_a <gcond *> (last);
+ edge branch_edge = get_cond_branch_to_split_loop (loop, cond);
+
+ if (branch_edge)
+ {
+ do_split_loop_on_cond (loop, branch_edge);
+ do_split = true;
+ break;
+ }
+ }
+
+ delete info;
+ loop->aux = NULL;
+
+ return do_split;
+}
+
/* Main entry point. Perform loop splitting on all suitable loops. */
static unsigned int
@@ -662,6 +1383,32 @@ tree_ssa_split_loops (void)
}
}
+ if (changed)
+ {
+ cleanup_tree_cfg ();
+ changed = false;
+ }
+
+ /* Perform loop splitting for suitable if-conditions in all loops. */
+ FOR_EACH_LOOP (loop, LI_INCLUDE_ROOT)
+ loop->aux = NULL;
+
+ FOR_EACH_LOOP (loop, LI_FROM_INNERMOST)
+ {
+ if (loop->aux)
+ {
+ loop_outer (loop)->aux = loop;
+ continue;
+ }
+
+ if (!optimize_loop_for_size_p (loop)
+ && split_loop_on_cond (loop))
+ {
+ loop_outer (loop)->aux = loop;
+ changed = true;
+ }
+ }
+
FOR_EACH_LOOP (loop, LI_INCLUDE_ROOT)
loop->aux = NULL;
--
2.17.1
