tree-ssa-ifcombine.cc File Reference

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "backend.h"
#include "rtl.h"
#include "tree.h"
#include "gimple.h"
#include "cfghooks.h"
#include "tree-pass.h"
#include "memmodel.h"
#include "tm_p.h"
#include "ssa.h"
#include "tree-pretty-print.h"
#include "fold-const.h"
#include "cfganal.h"
#include "gimple-iterator.h"
#include "gimple-fold.h"
#include "gimplify-me.h"
#include "tree-cfg.h"
#include "tree-ssa.h"
#include "tree-ssa-ifcombine.h"
#include "attribs.h"
#include "asan.h"
#include "bitmap.h"
#include "cfgloop.h"

Include dependency graph for tree-ssa-ifcombine.cc:

Data Structures
struct	ifcombine_mark_ssa_name_t

Macros
#define	LOGICAL_OP_NON_SHORT_CIRCUIT

Functions
static bool	known_succ_p (basic_block cond_bb)
bool	recognize_if_then_else (basic_block cond_bb, basic_block *then_bb, basic_block *else_bb, bool succs_any)
static bool	bb_no_side_effects_p (basic_block bb)
static bool	forwarder_block_to (basic_block bb, basic_block to_bb)
static bool	same_phi_args_p (basic_block bb1, basic_block bb2, basic_block dest)
static tree	get_name_for_bit_test (tree candidate)
static bool	recognize_single_bit_test (gcond *cond, tree *name, tree *bit, bool inv)
static bool	recognize_bits_test (gcond *cond, tree *name, tree *bits, bool inv)
static void	update_profile_after_ifcombine (basic_block inner_cond_bb, basic_block outer_cond_bb)
static void	ifcombine_mark_ssa_name (bitmap used, tree name, basic_block outer)
static tree	ifcombine_mark_ssa_name_walk (tree *t, int *, void *data_)
static void	ifcombine_rewrite_to_defined_overflow (gimple_stmt_iterator gsi)
static bool	ifcombine_replace_cond (gcond *inner_cond, bool inner_inv, gcond *outer_cond, bool outer_inv, tree cond, bool must_canon, tree cond2)
static bool	can_combine_bbs_with_short_circuit (basic_block inner_cond_bb, tree lhs, tree rhs)
static bool	bb_guards_loop_p (basic_block bb)
static bool	ifcombine_ifandif (basic_block inner_cond_bb, bool inner_inv, basic_block outer_cond_bb, bool outer_inv)
static bool	tree_ssa_ifcombine_bb_1 (basic_block inner_cond_bb, basic_block outer_cond_bb, basic_block then_bb, basic_block else_bb, basic_block phi_pred_bb, basic_block outer_succ_bb)
bool	tree_ssa_ifcombine_bb (basic_block inner_cond_bb)
gimple_opt_pass *	make_pass_tree_ifcombine (gcc::context *ctxt)

Macro Definition Documentation

LOGICAL_OP_NON_SHORT_CIRCUIT

#define LOGICAL_OP_NON_SHORT_CIRCUIT

Value:

(BRANCH_COST (optimize_function_for_speed_p (cfun), \
              false) >= 2)

Combining of if-expressions on trees.
   Copyright (C) 2007-2026 Free Software Foundation, Inc.
   Contributed by Richard Guenther <rguenther@suse.de>

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.   

rtl is needed only because arm back-end requires it for
BRANCH_COST.   

Function Documentation

bb_guards_loop_p()

bool bb_guards_loop_p ( basic_block bb )

static

Return true if BB guards entry to a loop: a successor edge reaches a loop
header BB does not belong to, directly or through a single-successor
preheader.  Combining the scalar conditions guarding a loop into a single
boolean leaves the number-of-iterations analysis unable to prove the loop
runs at least once, pessimizing later loop passes such as ivopts.   

References bb_loop_header_p(), CDI_DOMINATORS, dominated_by_p(), FOR_EACH_EDGE, single_succ(), single_succ_p(), and basic_block_def::succs.

Referenced by ifcombine_ifandif().

bb_no_side_effects_p()

bool bb_no_side_effects_p ( basic_block bb )

static

Verify if the basic block BB does not have side-effects.  Return
true in this case, else false.   

References dyn_cast(), FOR_EACH_SSA_TREE_OPERAND, gimple_assign_lhs(), gimple_assign_rhs2(), gimple_assign_rhs_code(), gimple_could_trap_p(), gimple_has_side_effects(), gimple_vdef(), gsi_end_p(), gsi_next(), gsi_start_bb(), gsi_stmt(), integer_minus_onep(), INTEGRAL_TYPE_P, is_gimple_call(), is_gimple_debug(), ssa_name_maybe_undef_p(), SSA_OP_USE, TREE_CODE, TREE_TYPE, and TYPE_OVERFLOW_UNDEFINED.

Referenced by tree_ssa_ifcombine_bb().

can_combine_bbs_with_short_circuit()

bool can_combine_bbs_with_short_circuit ( basic_block inner_cond_bb, tree lhs, tree rhs )

static

Returns true if inner_cond_bb contains just the condition or 1/2 statements
that define lhs or rhs with an integer conversion.  

References CONVERT_EXPR_CODE_P, gimple_assign_lhs(), gimple_assign_rhs_code(), gsi_next_nondebug(), gsi_one_before_end_p(), gsi_start_nondebug_after_labels_bb(), gsi_stmt(), i, and is_gimple_assign().

Referenced by ifcombine_ifandif().

forwarder_block_to()

bool forwarder_block_to ( basic_block bb, basic_block to_bb )

static

Return true if BB is an empty forwarder block to TO_BB.   

References empty_block_p(), single_succ(), and single_succ_p().

Referenced by tree_ssa_ifcombine_bb().

get_name_for_bit_test()

tree get_name_for_bit_test ( tree candidate )

static

Return the best representative SSA name for CANDIDATE which is used
in a bit test.   

References candidate(), CONVERT_EXPR_CODE_P, gimple_assign_rhs1(), gimple_assign_rhs_code(), has_single_use(), is_gimple_assign(), SSA_NAME_DEF_STMT, TREE_CODE, TREE_TYPE, and TYPE_PRECISION.

Referenced by recognize_bits_test(), and recognize_single_bit_test().

ifcombine_ifandif()

bool ifcombine_ifandif ( basic_block inner_cond_bb, bool inner_inv, basic_block outer_cond_bb, bool outer_inv )

static

If-convert on a and pattern with a common else block.  The inner
if is specified by its INNER_COND_BB, the outer by OUTER_COND_BB.
inner_inv, outer_inv indicate whether the conditions are inverted.
Returns true if the edges to the common else basic-block were merged.   

References bb_guards_loop_p(), boolean_type_node, build_int_cst(), can_combine_bbs_with_short_circuit(), dump_file, fold_build2, fold_build2_loc(), fold_convert, fold_truth_andor_for_ifcombine(), gimple_bb(), gimple_build(), gimple_cond_code(), gimple_cond_lhs(), gimple_cond_rhs(), gimple_location(), gsi_for_stmt(), gsi_last_bb(), GSI_SAME_STMT, HONOR_NANS(), ifcombine_replace_cond(), invert_tree_comparison(), LOGICAL_OP_NON_SHORT_CIRCUIT, loop_exits_from_bb_p(), basic_block_def::loop_father, maybe_fold_and_comparisons(), NULL_TREE, POINTER_TYPE_P, print_generic_expr(), recognize_bits_test(), recognize_single_bit_test(), safe_dyn_cast(), sanitize_coverage_p(), single_pred(), SSA_NAME_OCCURS_IN_ABNORMAL_PHI, tcc_comparison, TREE_CODE, TREE_CODE_CLASS, TREE_TYPE, TYPE_PRECISION, and unsigned_type_for().

Referenced by tree_ssa_ifcombine_bb_1().

ifcombine_mark_ssa_name()

void ifcombine_mark_ssa_name ( bitmap used, tree name, basic_block outer )

static

Set NAME's bit in USED if OUTER dominates it.   

References bitmap_set_bit, CDI_DOMINATORS, dominated_by_p(), gimple_bb(), SSA_NAME_DEF_STMT, SSA_NAME_IS_DEFAULT_DEF, SSA_NAME_VERSION, and TREE_CODE.

Referenced by ifcombine_mark_ssa_name_walk(), and ifcombine_replace_cond().

ifcombine_mark_ssa_name_walk()

tree ifcombine_mark_ssa_name_walk ( tree * t, int * , void * data_ )

static

Mark in DATA->used any SSA_NAMEs used in *t.   

References ifcombine_mark_ssa_name(), and NULL.

Referenced by ifcombine_replace_cond().

ifcombine_replace_cond()

bool ifcombine_replace_cond ( gcond * inner_cond, bool inner_inv, gcond * outer_cond, bool outer_inv, tree cond, bool must_canon, tree cond2 )

static

Replace the conditions in INNER_COND and OUTER_COND with COND and COND2.
COND and COND2 are computed for insertion at INNER_COND, with OUTER_COND
replaced with a constant, but if there are intervening blocks, it's best to
adjust COND for insertion at OUTER_COND, placing COND2 at INNER_COND.   

References a, bitmap_bit_p, bitmap_empty_p(), bitmap_tree_view(), boolean_false_node, boolean_true_node, canonicalize_cond_expr_cond(), dyn_cast(), end(), fold_build1, FOR_EACH_PHI_ARG, FOR_EACH_SSA_TREE_OPERAND, FOR_EACH_VEC_ELT, force_gimple_operand_gsi_1(), gcc_assert, gimple_bb(), gimple_build_assign(), gimple_cond_set_condition_from_tree(), gimple_phi_arg_def(), gimple_phi_arg_location(), gimple_phi_num_args(), gimple_phi_result(), gimple_set_location(), gsi_end_p(), gsi_for_phi(), gsi_for_stmt(), gsi_insert_before(), gsi_last_bb(), gsi_move_before(), GSI_NEW_STMT, gsi_next(), gsi_prev(), GSI_SAME_STMT, gsi_start_bb(), gsi_start_phis(), gsi_stmt(), i, ifcombine_mark_ssa_name(), ifcombine_mark_ssa_name_walk(), ifcombine_rewrite_to_defined_overflow(), is_gimple_condexpr_for_cond(), NULL, remove_phi_node(), reset_flow_sensitive_info(), reset_flow_sensitive_info_in_bb(), single_pred(), SSA_NAME_VERSION, SSA_OP_DEF, SSA_OP_USE, TREE_CODE, TREE_OPERAND, TREE_TYPE, update_profile_after_ifcombine(), update_stmt(), USE_FROM_PTR, and walk_tree.

Referenced by ifcombine_ifandif().

ifcombine_rewrite_to_defined_overflow()

void ifcombine_rewrite_to_defined_overflow ( gimple_stmt_iterator gsi )

inlinestatic

Rewrite a stmt, that presumably used to be guarded by conditions that could
avoid undefined overflow, into one that has well-defined overflow, so that
it won't invoke undefined behavior once the guarding conditions change.   

References gimple_needing_rewrite_undefined(), gsi_stmt(), and rewrite_to_defined_unconditional().

Referenced by ifcombine_replace_cond().

known_succ_p()

bool known_succ_p ( basic_block cond_bb )

static

Return FALSE iff the COND_BB ends with a conditional whose result is not a
known constant.   

References CONSTANT_CLASS_P, gimple_cond_lhs(), gimple_cond_rhs(), gsi_last_bb(), and safe_dyn_cast().

Referenced by recognize_if_then_else(), tree_ssa_ifcombine_bb(), and update_profile_after_ifcombine().

make_pass_tree_ifcombine()

gimple_opt_pass * make_pass_tree_ifcombine

(

gcc::context *

ctxt

)

recognize_bits_test()

bool recognize_bits_test ( gcond * cond, tree * name, tree * bits, bool inv )

static

Recognize a bit test pattern in a GIMPLE_COND and its defining
statements.  Store the name being tested in *NAME and the bits
in *BITS.  The COND_EXPR computes *NAME & *BITS.
Returns true if the pattern matched, false otherwise.   

References get_name_for_bit_test(), gimple_assign_rhs1(), gimple_assign_rhs2(), gimple_assign_rhs_code(), gimple_cond_code(), gimple_cond_lhs(), gimple_cond_rhs(), integer_zerop(), is_gimple_assign(), SSA_NAME_DEF_STMT, and TREE_CODE.

Referenced by ifcombine_ifandif().

recognize_if_then_else()

bool recognize_if_then_else	(	basic_block	cond_bb,
		basic_block *	then_bb,
		basic_block *	else_bb,
		bool	succs_any = false )

This pass combines COND_EXPRs to simplify control flow.  It
currently recognizes bit tests and comparisons in chains that
represent logical and or logical or of two COND_EXPRs.

It does so by walking basic blocks in a approximate reverse
post-dominator order and trying to match CFG patterns that
represent logical and or logical or of two COND_EXPRs.
Transformations are done if the COND_EXPR conditions match
either

  1. two single bit tests X & (1 << Yn) (for logical and)

  2. two bit tests X & Yn (for logical or)

  3. two comparisons X OPn Y (for logical or)

To simplify this pass, removing basic blocks and dead code
is left to CFG cleanup and DCE.   

Recognize a if-then-else CFG pattern starting to match with the COND_BB
basic-block containing the COND_EXPR.  If !SUCCS_ANY, the condition must not
resolve to a constant for a match.  Returns true if the pattern matched,
false otherwise.  In case of a !SUCCS_ANY match, the recognized then end
else blocks are stored to *THEN_BB and *ELSE_BB.  If *THEN_BB and/or
*ELSE_BB are already set, they are required to match the then and else
basic-blocks to make the pattern match.  If SUCCS_ANY, *THEN_BB and *ELSE_BB
will not be filled in, and they will be found to match even if reversed.   

Copyright (C) 2026 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 3, or (at your option) any
later version.

GCC is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.   

References EDGE_COUNT, EDGE_SUCC, known_succ_p(), and basic_block_def::succs.

Referenced by apply_clusters(), tree_ssa_ifcombine_bb(), and tree_ssa_ifcombine_bb_1().

recognize_single_bit_test()

bool recognize_single_bit_test ( gcond * cond, tree * name, tree * bit, bool inv )

static

Recognize a single bit test pattern in GIMPLE_COND and its defining
statements.  Store the name being tested in *NAME and the bit
in *BIT.  The GIMPLE_COND computes *NAME & (1 << *BIT).
Returns true if the pattern matched, false otherwise.   

References build_int_cst(), CONVERT_EXPR_CODE_P, get_name_for_bit_test(), gimple_assign_lhs(), gimple_assign_rhs1(), gimple_assign_rhs2(), gimple_assign_rhs_code(), gimple_assign_ssa_name_copy_p(), gimple_cond_code(), gimple_cond_lhs(), gimple_cond_rhs(), integer_onep(), integer_pow2p(), integer_type_node, integer_zero_node, integer_zerop(), is_gimple_assign(), SSA_NAME_DEF_STMT, TREE_CODE, tree_log2(), TREE_TYPE, and TYPE_PRECISION.

Referenced by ifcombine_ifandif().

same_phi_args_p()

bool same_phi_args_p ( basic_block bb1, basic_block bb2, basic_block dest )

static

Verify if all PHI node arguments in DEST for edges from BB1 or
BB2 to DEST are the same.  This makes the CFG merge point
free from side-effects.  Return true in this case, else false.   

References find_edge(), gsi_end_p(), gsi_next(), gsi_start_phis(), operand_equal_p(), gphi_iterator::phi(), and PHI_ARG_DEF_FROM_EDGE.

Referenced by tree_ssa_ifcombine_bb(), and tree_ssa_ifcombine_bb_1().

tree_ssa_ifcombine_bb()

bool tree_ssa_ifcombine_bb

(

basic_block

inner_cond_bb

)

Recognize a CFG pattern and dispatch to the appropriate
if-conversion helper.  We start with BB as the innermost
worker basic-block.  Returns true if a transformation was done.   

References bb_no_side_effects_p(), changed, forwarder_block_to(), known_succ_p(), NULL, recognize_if_then_else(), same_phi_args_p(), single_pred(), single_pred_p(), single_succ_p(), and tree_ssa_ifcombine_bb_1().

Referenced by tail_merge_optimize().

tree_ssa_ifcombine_bb_1()

bool tree_ssa_ifcombine_bb_1 ( basic_block inner_cond_bb, basic_block outer_cond_bb, basic_block then_bb, basic_block else_bb, basic_block phi_pred_bb, basic_block outer_succ_bb )

static

Helper function for tree_ssa_ifcombine_bb.  Recognize a CFG pattern and
dispatch to the appropriate if-conversion helper for a particular
set of INNER_COND_BB, OUTER_COND_BB, THEN_BB and ELSE_BB.
PHI_PRED_BB should be one of INNER_COND_BB, THEN_BB or ELSE_BB.
OUTER_SUCC_BB is the successor of OUTER_COND_BB on the path towards
INNER_COND_BB.   

References ifcombine_ifandif(), recognize_if_then_else(), and same_phi_args_p().

Referenced by tree_ssa_ifcombine_bb().

update_profile_after_ifcombine()

void update_profile_after_ifcombine ( basic_block inner_cond_bb, basic_block outer_cond_bb )

static

Update profile after code in either outer_cond_bb or inner_cond_bb was
adjusted so that it has no condition.   

References profile_probability::always(), basic_block_def::count, EDGE_SUCC, profile_probability::even(), find_edge(), gcc_assert, known_succ_p(), profile_probability::never(), single_pred(), and single_pred_p().

Referenced by ifcombine_replace_cond().