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/* Conditional Dead Call Elimination pass for the GNU compiler.
Copyright (C) 2008-2019 Free Software Foundation, Inc.
Contributed by Xinliang David Li <>
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
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
<>. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "backend.h"
#include "tree.h"
#include "gimple.h"
#include "cfghooks.h"
#include "tree-pass.h"
#include "ssa.h"
#include "gimple-pretty-print.h"
#include "fold-const.h"
#include "stor-layout.h"
#include "gimple-iterator.h"
#include "tree-cfg.h"
#include "tree-into-ssa.h"
#include "builtins.h"
#include "internal-fn.h"
#include "tree-dfa.h"
/* This pass serves two closely-related purposes:
1. It conditionally executes calls that set errno if (a) the result of
the call is unused and (b) a simple range check on the arguments can
detect most cases where errno does not need to be set.
This is the "conditional dead-code elimination" that gave the pass
its original name, since the call is dead for most argument values.
The calls for which it helps are usually part of the C++ abstraction
penalty exposed after inlining.
2. It looks for calls to built-in functions that set errno and whose
result is used. It checks whether there is an associated internal
function that doesn't set errno and whether the target supports
that internal function. If so, the pass uses the internal function
to compute the result of the built-in function but still arranges
for errno to be set when necessary. There are two ways of setting
a. by protecting the original call with the same argument checks as (1)
b. by protecting the original call with a check that the result
of the internal function is not equal to itself (i.e. is NaN).
(b) requires that NaNs are the only erroneous results. It is not
appropriate for functions like log, which returns ERANGE for zero
arguments. (b) is also likely to perform worse than (a) because it
requires the result to be calculated first. The pass therefore uses
(a) when it can and uses (b) as a fallback.
For (b) the pass can replace the original call with a call to
IFN_SET_EDOM, if the target supports direct assignments to errno.
In both cases, arguments that require errno to be set should occur
rarely in practice. Checks of the errno result should also be rare,
but the compiler would need powerful interprocedural analysis to
prove that errno is not checked. It's much easier to add argument
checks or result checks instead.
An example of (1) is:
log (x); // Mostly dead call
if (__builtin_islessequal (x, 0))
log (x);
With this change, call to log (x) is effectively eliminated, as
in the majority of the cases, log won't be called with x out of
range. The branch is totally predictable, so the branch cost
is low.
An example of (2) is:
y = sqrt (x);
y = IFN_SQRT (x);
if (__builtin_isless (x, 0))
sqrt (x);
In the vast majority of cases we should then never need to call sqrt.
Note that library functions are not supposed to clear errno to zero without
error. See IEEE Std 1003.1, section 2.3 Error Numbers, and section 7.5:3 of
ISO/IEC 9899 (C99).
The condition wrapping the builtin call is conservatively set to avoid too
aggressive (wrong) shrink wrapping. */
/* A structure for representing input domain of
a function argument in integer. If the lower
bound is -inf, has_lb is set to false. If the
upper bound is +inf, has_ub is false.
is_lb_inclusive and is_ub_inclusive are flags
to indicate if lb and ub value are inclusive
respectively. */
struct inp_domain
int lb;
int ub;
bool has_lb;
bool has_ub;
bool is_lb_inclusive;
bool is_ub_inclusive;
/* A helper function to construct and return an input
domain object. LB is the lower bound, HAS_LB is
a boolean flag indicating if the lower bound exists,
and LB_INCLUSIVE is a boolean flag indicating if the
lower bound is inclusive or not. UB, HAS_UB, and
UB_INCLUSIVE have the same meaning, but for upper
bound of the domain. */
static inp_domain
get_domain (int lb, bool has_lb, bool lb_inclusive,
int ub, bool has_ub, bool ub_inclusive)
inp_domain domain; = lb;
domain.has_lb = has_lb;
domain.is_lb_inclusive = lb_inclusive;
domain.ub = ub;
domain.has_ub = has_ub;
domain.is_ub_inclusive = ub_inclusive;
return domain;
/* A helper function to check the target format for the
argument type. In this implementation, only IEEE formats
are supported. ARG is the call argument to be checked.
Returns true if the format is supported. To support other
target formats, function get_no_error_domain needs to be
enhanced to have range bounds properly computed. Since
the check is cheap (very small number of candidates
to be checked), the result is not cached for each float type. */
static bool
check_target_format (tree arg)
tree type;
machine_mode mode;
const struct real_format *rfmt;
type = TREE_TYPE (arg);
mode = TYPE_MODE (type);
rfmt = REAL_MODE_FORMAT (mode);
if ((mode == SFmode
&& (rfmt == &ieee_single_format || rfmt == &mips_single_format
|| rfmt == &motorola_single_format))
|| (mode == DFmode
&& (rfmt == &ieee_double_format || rfmt == &mips_double_format
|| rfmt == &motorola_double_format))
/* For long double, we cannot really check XFmode
which is only defined on intel platforms.
Candidate pre-selection using builtin function
code guarantees that we are checking formats
for long double modes: double, quad, and extended. */
|| (mode != SFmode && mode != DFmode
&& (rfmt == &ieee_quad_format
|| rfmt == &mips_quad_format
|| rfmt == &ieee_extended_motorola_format
|| rfmt == &ieee_extended_intel_96_format
|| rfmt == &ieee_extended_intel_128_format
|| rfmt == &ieee_extended_intel_96_round_53_format)))
return true;
return false;
/* A helper function to help select calls to pow that are suitable for
conditional DCE transformation. It looks for pow calls that can be
guided with simple conditions. Such calls either have constant base
values or base values converted from integers. Returns true if
the pow call POW_CALL is a candidate. */
/* The maximum integer bit size for base argument of a pow call
that is suitable for shrink-wrapping transformation. */
static bool
check_pow (gcall *pow_call)
tree base, expn;
enum tree_code bc, ec;
if (gimple_call_num_args (pow_call) != 2)
return false;
base = gimple_call_arg (pow_call, 0);
expn = gimple_call_arg (pow_call, 1);
if (!check_target_format (expn))
return false;
bc = TREE_CODE (base);
ec = TREE_CODE (expn);
/* Folding candidates are not interesting.
Can actually assert that it is already folded. */
if (ec == REAL_CST && bc == REAL_CST)
return false;
if (bc == REAL_CST)
/* Only handle a fixed range of constant. */
if (real_equal (&bcv, &dconst1))
return false;
if (real_less (&bcv, &dconst1))
return false;
real_from_integer (&mv, TYPE_MODE (TREE_TYPE (base)), 256, UNSIGNED);
if (real_less (&mv, &bcv))
return false;
return true;
else if (bc == SSA_NAME)
tree base_val0, type;
gimple *base_def;
int bit_sz;
/* Only handles cases where base value is converted
from integer values. */
base_def = SSA_NAME_DEF_STMT (base);
if (gimple_code (base_def) != GIMPLE_ASSIGN)
return false;
if (gimple_assign_rhs_code (base_def) != FLOAT_EXPR)
return false;
base_val0 = gimple_assign_rhs1 (base_def);
type = TREE_TYPE (base_val0);
return false;
bit_sz = TYPE_PRECISION (type);
/* If the type of the base is too wide,
the resulting shrink wrapping condition
will be too conservative. */
if (bit_sz > MAX_BASE_INT_BIT_SIZE)
return false;
return true;
return false;
/* A helper function to help select candidate function calls that are
suitable for conditional DCE. Candidate functions must have single
valid input domain in this implementation except for pow (see check_pow).
Returns true if the function call is a candidate. */
static bool
check_builtin_call (gcall *bcall)
tree arg;
arg = gimple_call_arg (bcall, 0);
return check_target_format (arg);
/* Return true if built-in function call CALL calls a math function
and if we know how to test the range of its arguments to detect _most_
situations in which errno is not set. The test must err on the side
of treating non-erroneous values as potentially erroneous. */
static bool
can_test_argument_range (gcall *call)
switch (DECL_FUNCTION_CODE (gimple_call_fndecl (call)))
/* Trig functions. */
/* Hyperbolic functions. */
/* Log functions. */
/* Exp functions. */
/* Sqrt. */
return check_builtin_call (call);
/* Special one: two argument pow. */
return check_pow (call);
return false;
/* Return true if CALL can produce a domain error (EDOM) but can never
produce a pole, range overflow or range underflow error (all ERANGE).
This means that we can tell whether a function would have set errno
by testing whether the result is a NaN. */
static bool
edom_only_function (gcall *call)
switch (DECL_FUNCTION_CODE (gimple_call_fndecl (call)))
return true;
return false;
/* Return true if it is structurally possible to guard CALL. */
static bool
can_guard_call_p (gimple *call)
return (!stmt_ends_bb_p (call)
|| find_fallthru_edge (gimple_bb (call)->succs));
/* For a comparison code return the comparison code we should use if we don't
static enum tree_code
comparison_code_if_no_nans (tree_code code)
switch (code)
return LT_EXPR;
return GT_EXPR;
return LE_EXPR;
return GE_EXPR;
return EQ_EXPR;
return NE_EXPR;
case LT_EXPR:
case GT_EXPR:
case LE_EXPR:
case GE_EXPR:
case EQ_EXPR:
case NE_EXPR:
return code;
gcc_unreachable ();
/* A helper function to generate gimple statements for one bound
comparison, so that the built-in function is called whenever
TCODE <ARG, LBUB> is *false*. TEMP_NAME1/TEMP_NAME2 are names
of the temporaries, CONDS is a vector holding the produced GIMPLE
statements, and NCONDS points to the variable holding the number of
logical comparisons. CONDS is either empty or a list ended with a
null tree. */
static void
gen_one_condition (tree arg, int lbub,
enum tree_code tcode,
const char *temp_name1,
const char *temp_name2,
vec<gimple *> conds,
unsigned *nconds)
if (!HONOR_NANS (arg))
tcode = comparison_code_if_no_nans (tcode);
tree lbub_real_cst, lbub_cst, float_type;
tree temp, tempn, tempc, tempcn;
gassign *stmt1;
gassign *stmt2;
gcond *stmt3;
float_type = TREE_TYPE (arg);
lbub_cst = build_int_cst (integer_type_node, lbub);
lbub_real_cst = build_real_from_int_cst (float_type, lbub_cst);
temp = create_tmp_var (float_type, temp_name1);
stmt1 = gimple_build_assign (temp, arg);
tempn = make_ssa_name (temp, stmt1);
gimple_assign_set_lhs (stmt1, tempn);
tempc = create_tmp_var (boolean_type_node, temp_name2);
stmt2 = gimple_build_assign (tempc,
fold_build2 (tcode,
tempn, lbub_real_cst));
tempcn = make_ssa_name (tempc, stmt2);
gimple_assign_set_lhs (stmt2, tempcn);
stmt3 = gimple_build_cond_from_tree (tempcn, NULL_TREE, NULL_TREE);
conds.quick_push (stmt1);
conds.quick_push (stmt2);
conds.quick_push (stmt3);
/* A helper function to generate GIMPLE statements for
out of input domain check. ARG is the call argument
to be runtime checked, DOMAIN holds the valid domain
for the given function, CONDS points to the vector
holding the result GIMPLE statements. *NCONDS is
the number of logical comparisons. This function
produces no more than two logical comparisons, one
for lower bound check, one for upper bound check. */
static void
gen_conditions_for_domain (tree arg, inp_domain domain,
vec<gimple *> conds,
unsigned *nconds)
if (domain.has_lb)
gen_one_condition (arg,,
conds, nconds);
if (domain.has_ub)
/* Now push a separator. */
if (domain.has_lb)
conds.quick_push (NULL);
gen_one_condition (arg, domain.ub,
conds, nconds);
/* A helper function to generate condition
code for the y argument in call pow (some_const, y).
See candidate selection in check_pow. Since the
candidates' base values have a limited range,
the guarded code generated for y are simple:
if (__builtin_isgreater (y, max_y))
pow (const, y);
Note max_y can be computed separately for each
const base, but in this implementation, we
choose to compute it using the max base
in the allowed range for the purpose of
simplicity. BASE is the constant base value,
EXPN is the expression for the exponent argument,
*CONDS is the vector to hold resulting statements,
and *NCONDS is the number of logical conditions. */
static void
gen_conditions_for_pow_cst_base (tree base, tree expn,
vec<gimple *> conds,
unsigned *nconds)
inp_domain exp_domain;
/* Validate the range of the base constant to make
sure it is consistent with check_pow. */
gcc_assert (!real_equal (&bcv, &dconst1)
&& !real_less (&bcv, &dconst1));
real_from_integer (&mv, TYPE_MODE (TREE_TYPE (base)), 256, UNSIGNED);
gcc_assert (!real_less (&mv, &bcv));
exp_domain = get_domain (0, false, false,
127, true, false);
gen_conditions_for_domain (expn, exp_domain,
conds, nconds);
/* Generate error condition code for pow calls with
non constant base values. The candidates selected
have their base argument value converted from
integer (see check_pow) value (1, 2, 4 bytes), and
the max exp value is computed based on the size
of the integer type (i.e. max possible base value).
The resulting input domain for exp argument is thus
conservative (smaller than the max value allowed by
the runtime value of the base). BASE is the integer
base value, EXPN is the expression for the exponent
argument, *CONDS is the vector to hold resulting
statements, and *NCONDS is the number of logical
conditions. */
static void
gen_conditions_for_pow_int_base (tree base, tree expn,
vec<gimple *> conds,
unsigned *nconds)
gimple *base_def;
tree base_val0;
tree int_type;
tree temp, tempn;
tree cst0;
gimple *stmt1, *stmt2;
int bit_sz, max_exp;
inp_domain exp_domain;
base_def = SSA_NAME_DEF_STMT (base);
base_val0 = gimple_assign_rhs1 (base_def);
int_type = TREE_TYPE (base_val0);
bit_sz = TYPE_PRECISION (int_type);
gcc_assert (bit_sz > 0
&& bit_sz <= MAX_BASE_INT_BIT_SIZE);
/* Determine the max exp argument value according to
the size of the base integer. The max exp value
is conservatively estimated assuming IEEE754 double
precision format. */
if (bit_sz == 8)
max_exp = 128;
else if (bit_sz == 16)
max_exp = 64;
gcc_assert (bit_sz == MAX_BASE_INT_BIT_SIZE);
max_exp = 32;
/* For pow ((double)x, y), generate the following conditions:
cond 1:
temp1 = x;
if (__builtin_islessequal (temp1, 0))
cond 2:
temp2 = y;
if (__builtin_isgreater (temp2, max_exp_real_cst)) */
/* Generate condition in reverse order -- first
the condition for the exp argument. */
exp_domain = get_domain (0, false, false,
max_exp, true, true);
gen_conditions_for_domain (expn, exp_domain,
conds, nconds);
/* Now generate condition for the base argument.
Note it does not use the helper function
gen_conditions_for_domain because the base
type is integer. */
/* Push a separator. */
conds.quick_push (NULL);
temp = create_tmp_var (int_type, "DCE_COND1");
cst0 = build_int_cst (int_type, 0);
stmt1 = gimple_build_assign (temp, base_val0);
tempn = make_ssa_name (temp, stmt1);
gimple_assign_set_lhs (stmt1, tempn);
stmt2 = gimple_build_cond (GT_EXPR, tempn, cst0, NULL_TREE, NULL_TREE);
conds.quick_push (stmt1);
conds.quick_push (stmt2);
/* Method to generate conditional statements for guarding conditionally
dead calls to pow. One or more statements can be generated for
each logical condition. Statement groups of different conditions
are separated by a NULL tree and they are stored in the vec
conds. The number of logical conditions are stored in *nconds.
See C99 standard,, for description of pow (x, y).
The precise condition for domain errors are complex. In this
implementation, a simplified (but conservative) valid domain
for x and y are used: x is positive to avoid dom errors, while
y is smaller than a upper bound (depending on x) to avoid range
errors. Runtime code is generated to check x (if not constant)
and y against the valid domain. If it is out, jump to the call,
otherwise the call is bypassed. POW_CALL is the call statement,
*CONDS is a vector holding the resulting condition statements,
and *NCONDS is the number of logical conditions. */
static void
gen_conditions_for_pow (gcall *pow_call, vec<gimple *> conds,
unsigned *nconds)
tree base, expn;
enum tree_code bc;
gcc_checking_assert (check_pow (pow_call));
*nconds = 0;
base = gimple_call_arg (pow_call, 0);
expn = gimple_call_arg (pow_call, 1);
bc = TREE_CODE (base);
if (bc == REAL_CST)
gen_conditions_for_pow_cst_base (base, expn, conds, nconds);
else if (bc == SSA_NAME)
gen_conditions_for_pow_int_base (base, expn, conds, nconds);
gcc_unreachable ();
/* A helper routine to help computing the valid input domain
for a builtin function. See C99 7.12.7 for details. In this
implementation, we only handle single region domain. The
resulting region can be conservative (smaller) than the actual
one and rounded to integers. Some of the bounds are documented
in the standard, while other limit constants are computed
assuming IEEE floating point format (for SF and DF modes).
Since IEEE only sets minimum requirements for long double format,
different long double formats exist under different implementations
(e.g, 64 bit double precision (DF), 80 bit double-extended
precision (XF), and 128 bit quad precision (QF) ). For simplicity,
in this implementation, the computed bounds for long double assume
64 bit format (DF), and are therefore conservative. Another
assumption is that single precision float type is always SF mode,
and double type is DF mode. This function is quite
implementation specific, so it may not be suitable to be part of
builtins.c. This needs to be revisited later to see if it can
be leveraged in x87 assembly expansion. */
static inp_domain
get_no_error_domain (enum built_in_function fnc)
switch (fnc)
/* Trig functions: return [-1, +1] */
return get_domain (-1, true, true,
1, true, true);
/* Hyperbolic functions. */
/* acosh: [1, +inf) */
return get_domain (1, true, true,
1, false, false);
/* atanh: (-1, +1) */
return get_domain (-1, true, false,
1, true, false);
/* coshf: (-89, +89) */
return get_domain (-89, true, false,
89, true, false);
/* cosh: (-710, +710) */
return get_domain (-710, true, false,
710, true, false);
/* Log functions: (0, +inf) */
return get_domain (0, true, false,
0, false, false);
return get_domain (-1, true, false,
0, false, false);
/* Exp functions. */
/* expf: (-inf, 88) */
return get_domain (-1, false, false,
88, true, false);
/* exp: (-inf, 709) */
return get_domain (-1, false, false,
709, true, false);
/* exp2f: (-inf, 128) */
return get_domain (-1, false, false,
128, true, false);
/* exp2: (-inf, 1024) */
return get_domain (-1, false, false,
1024, true, false);
/* exp10f: (-inf, 38) */
return get_domain (-1, false, false,
38, true, false);
case BUILT_IN_EXP10:
case BUILT_IN_POW10:
/* exp10: (-inf, 308) */
return get_domain (-1, false, false,
308, true, false);
/* sqrt: [0, +inf) */
return get_domain (0, true, true,
0, false, false);
gcc_unreachable ();
gcc_unreachable ();
/* The function to generate shrink wrap conditions for a partially
dead builtin call whose return value is not used anywhere,
but has to be kept live due to potential error condition.
BI_CALL is the builtin call, CONDS is the vector of statements
for condition code, NCODES is the pointer to the number of
logical conditions. Statements belonging to different logical
condition are separated by NULL tree in the vector. */
static void
gen_shrink_wrap_conditions (gcall *bi_call, vec<gimple *> conds,
unsigned int *nconds)
gcall *call;
tree fn;
enum built_in_function fnc;
gcc_assert (nconds && conds.exists ());
gcc_assert (conds.length () == 0);
gcc_assert (is_gimple_call (bi_call));
call = bi_call;
fn = gimple_call_fndecl (call);
gcc_assert (fn && fndecl_built_in_p (fn));
*nconds = 0;
if (fnc == BUILT_IN_POW)
gen_conditions_for_pow (call, conds, nconds);
tree arg;
inp_domain domain = get_no_error_domain (fnc);
*nconds = 0;
arg = gimple_call_arg (bi_call, 0);
gen_conditions_for_domain (arg, domain, conds, nconds);
/* Shrink-wrap BI_CALL so that it is only called when one of the NCONDS
conditions in CONDS is false. */
static void
shrink_wrap_one_built_in_call_with_conds (gcall *bi_call, vec <gimple *> conds,
unsigned int nconds)
gimple_stmt_iterator bi_call_bsi;
basic_block bi_call_bb, join_tgt_bb, guard_bb;
edge join_tgt_in_edge_from_call, join_tgt_in_edge_fall_thru;
edge bi_call_in_edge0, guard_bb_in_edge;
unsigned tn_cond_stmts;
unsigned ci;
gimple *cond_expr = NULL;
gimple *cond_expr_start;
/* The cfg we want to create looks like this:
[guard n-1] <- guard_bb (old block)
| \
| [guard n-2] }
| / \ }
| / ... } new blocks
| / [guard 0] }
| / / | }
[ call ] | <- bi_call_bb }
| \ |
| \ |
| [ join ] <- join_tgt_bb (old iff call must end bb)
possible EH edges (only if [join] is old)
When [join] is new, the immediate dominators for these blocks are:
1. [guard n-1]: unchanged
2. [call]: [guard n-1]
3. [guard m]: [guard m+1] for 0 <= m <= n-2
4. [join]: [guard n-1]
We punt for the more complex case case of [join] being old and
simply free the dominance info. We also punt on postdominators,
which aren't expected to be available at this point anyway. */
bi_call_bb = gimple_bb (bi_call);
/* Now find the join target bb -- split bi_call_bb if needed. */
if (stmt_ends_bb_p (bi_call))
/* We checked that there was a fallthrough edge in
can_guard_call_p. */
join_tgt_in_edge_from_call = find_fallthru_edge (bi_call_bb->succs);
gcc_assert (join_tgt_in_edge_from_call);
/* We don't want to handle PHIs. */
if (EDGE_COUNT (join_tgt_in_edge_from_call->dest->preds) > 1)
join_tgt_bb = split_edge (join_tgt_in_edge_from_call);
join_tgt_bb = join_tgt_in_edge_from_call->dest;
/* We may have degenerate PHIs in the destination. Propagate
those out. */
for (gphi_iterator i = gsi_start_phis (join_tgt_bb); !gsi_end_p (i);)
gphi *phi = i.phi ();
replace_uses_by (gimple_phi_result (phi),
gimple_phi_arg_def (phi, 0));
remove_phi_node (&i, true);
join_tgt_in_edge_from_call = split_block (bi_call_bb, bi_call);
join_tgt_bb = join_tgt_in_edge_from_call->dest;
bi_call_bsi = gsi_for_stmt (bi_call);
/* Now it is time to insert the first conditional expression
into bi_call_bb and split this bb so that bi_call is
shrink-wrapped. */
tn_cond_stmts = conds.length ();
cond_expr = NULL;
cond_expr_start = conds[0];
for (ci = 0; ci < tn_cond_stmts; ci++)
gimple *c = conds[ci];
gcc_assert (c || ci != 0);
if (!c)
gsi_insert_before (&bi_call_bsi, c, GSI_SAME_STMT);
cond_expr = c;
gcc_assert (cond_expr && gimple_code (cond_expr) == GIMPLE_COND);
typedef std::pair<edge, edge> edge_pair;
auto_vec<edge_pair, 8> edges;
bi_call_in_edge0 = split_block (bi_call_bb, cond_expr);
bi_call_in_edge0->flags &= ~EDGE_FALLTHRU;
bi_call_in_edge0->flags |= EDGE_FALSE_VALUE;
guard_bb = bi_call_bb;
bi_call_bb = bi_call_in_edge0->dest;
join_tgt_in_edge_fall_thru = make_edge (guard_bb, join_tgt_bb,
edges.reserve (nconds);
edges.quick_push (edge_pair (bi_call_in_edge0, join_tgt_in_edge_fall_thru));
/* Code generation for the rest of the conditions */
for (unsigned int i = 1; i < nconds; ++i)
unsigned ci0;
edge bi_call_in_edge;
gimple_stmt_iterator guard_bsi = gsi_for_stmt (cond_expr_start);
ci0 = ci;
cond_expr_start = conds[ci0];
for (; ci < tn_cond_stmts; ci++)
gimple *c = conds[ci];
gcc_assert (c || ci != ci0);
if (!c)
gsi_insert_before (&guard_bsi, c, GSI_SAME_STMT);
cond_expr = c;
gcc_assert (cond_expr && gimple_code (cond_expr) == GIMPLE_COND);
guard_bb_in_edge = split_block (guard_bb, cond_expr);
guard_bb_in_edge->flags &= ~EDGE_FALLTHRU;
guard_bb_in_edge->flags |= EDGE_TRUE_VALUE;
bi_call_in_edge = make_edge (guard_bb, bi_call_bb, EDGE_FALSE_VALUE);
edges.quick_push (edge_pair (bi_call_in_edge, guard_bb_in_edge));
/* Now update the probability and profile information, processing the
guards in order of execution.
There are two approaches we could take here. On the one hand we
could assign a probability of X to the call block and distribute
that probability among its incoming edges. On the other hand we
could assign a probability of X to each individual call edge.
The choice only affects calls that have more than one condition.
In those cases, the second approach would give the call block
a greater probability than the first. However, the difference
is only small, and our chosen X is a pure guess anyway.
Here we take the second approach because it's slightly simpler
and because it's easy to see that it doesn't lose profile counts. */
bi_call_bb->count = profile_count::zero ();
while (!edges.is_empty ())
edge_pair e = edges.pop ();
edge call_edge = e.first;
edge nocall_edge = e.second;
basic_block src_bb = call_edge->src;
gcc_assert (src_bb == nocall_edge->src);
call_edge->probability = profile_probability::very_unlikely ();
nocall_edge->probability = profile_probability::always ()
- call_edge->probability;
bi_call_bb->count += call_edge->count ();
if (nocall_edge->dest != join_tgt_bb)
nocall_edge->dest->count = src_bb->count - bi_call_bb->count;
if (dom_info_available_p (CDI_DOMINATORS))
/* The split_blocks leave [guard 0] as the immediate dominator
of [call] and [call] as the immediate dominator of [join].
Fix them up. */
set_immediate_dominator (CDI_DOMINATORS, bi_call_bb, guard_bb);
set_immediate_dominator (CDI_DOMINATORS, join_tgt_bb, guard_bb);
if (dump_file && (dump_flags & TDF_DETAILS))
location_t loc;
loc = gimple_location (bi_call);
fprintf (dump_file,
"%s:%d: note: function call is shrink-wrapped"
" into error conditions.\n",
/* Shrink-wrap BI_CALL so that it is only called when it might set errno
(but is always called if it would set errno). */
static void
shrink_wrap_one_built_in_call (gcall *bi_call)
unsigned nconds = 0;
auto_vec<gimple *, 12> conds;
gen_shrink_wrap_conditions (bi_call, conds, &nconds);
gcc_assert (nconds != 0);
shrink_wrap_one_built_in_call_with_conds (bi_call, conds, nconds);
/* Return true if built-in function call CALL could be implemented using
a combination of an internal function to compute the result and a
separate call to set errno. */
static bool
can_use_internal_fn (gcall *call)
/* Only replace calls that set errno. */
if (!gimple_vdef (call))
return false;
/* See whether there is an internal function for this built-in. */
if (replacement_internal_fn (call) == IFN_LAST)
return false;
/* See whether we can catch all cases where errno would be set,
while still avoiding the call in most cases. */
if (!can_test_argument_range (call)
&& !edom_only_function (call))
return false;
return true;
/* Implement built-in function call CALL using an internal function. */
static void
use_internal_fn (gcall *call)
/* We'll be inserting another call with the same arguments after the
lhs has been set, so prevent any possible coalescing failure from
having both values live at once. See PR 71020. */
replace_abnormal_ssa_names (call);
unsigned nconds = 0;
auto_vec<gimple *, 12> conds;
if (can_test_argument_range (call))
gen_shrink_wrap_conditions (call, conds, &nconds);
gcc_assert (nconds != 0);
gcc_assert (edom_only_function (call));
internal_fn ifn = replacement_internal_fn (call);
gcc_assert (ifn != IFN_LAST);
/* Construct the new call, with the same arguments as the original one. */
auto_vec <tree, 16> args;
unsigned int nargs = gimple_call_num_args (call);
for (unsigned int i = 0; i < nargs; ++i)
args.safe_push (gimple_call_arg (call, i));
gcall *new_call = gimple_build_call_internal_vec (ifn, args);
gimple_set_location (new_call, gimple_location (call));
gimple_call_set_nothrow (new_call, gimple_call_nothrow_p (call));
/* Transfer the LHS to the new call. */
tree lhs = gimple_call_lhs (call);
gimple_call_set_lhs (new_call, lhs);
gimple_call_set_lhs (call, NULL_TREE);
SSA_NAME_DEF_STMT (lhs) = new_call;
/* Insert the new call. */
gimple_stmt_iterator gsi = gsi_for_stmt (call);
gsi_insert_before (&gsi, new_call, GSI_SAME_STMT);
if (nconds == 0)
/* Skip the call if LHS == LHS. If we reach here, EDOM is the only
valid errno value and it is used iff the result is NaN. */
conds.quick_push (gimple_build_cond (EQ_EXPR, lhs, lhs,
/* Try replacing the original call with a direct assignment to
errno, via an internal function. */
if (set_edom_supported_p () && !stmt_ends_bb_p (call))
gimple_stmt_iterator gsi = gsi_for_stmt (call);
gcall *new_call = gimple_build_call_internal (IFN_SET_EDOM, 0);
gimple_set_vuse (new_call, gimple_vuse (call));
gimple_set_vdef (new_call, gimple_vdef (call));
SSA_NAME_DEF_STMT (gimple_vdef (new_call)) = new_call;
gimple_set_location (new_call, gimple_location (call));
gsi_replace (&gsi, new_call, false);
call = new_call;
shrink_wrap_one_built_in_call_with_conds (call, conds, nconds);
/* The top level function for conditional dead code shrink
wrapping transformation. */
static void
shrink_wrap_conditional_dead_built_in_calls (vec<gcall *> calls)
unsigned i = 0;
unsigned n = calls.length ();
for (; i < n ; i++)
gcall *bi_call = calls[i];
if (gimple_call_lhs (bi_call))
use_internal_fn (bi_call);
shrink_wrap_one_built_in_call (bi_call);
namespace {
const pass_data pass_data_call_cdce =
GIMPLE_PASS, /* type */
"cdce", /* name */
OPTGROUP_NONE, /* optinfo_flags */
TV_TREE_CALL_CDCE, /* tv_id */
( PROP_cfg | PROP_ssa ), /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
0, /* todo_flags_finish */
class pass_call_cdce : public gimple_opt_pass
pass_call_cdce (gcc::context *ctxt)
: gimple_opt_pass (pass_data_call_cdce, ctxt)
/* opt_pass methods: */
virtual bool gate (function *)
/* The limit constants used in the implementation
assume IEEE floating point format. Other formats
can be supported in the future if needed. */
return flag_tree_builtin_call_dce != 0;
virtual unsigned int execute (function *);
}; // class pass_call_cdce
unsigned int
pass_call_cdce::execute (function *fun)
basic_block bb;
gimple_stmt_iterator i;
auto_vec<gcall *> cond_dead_built_in_calls;
FOR_EACH_BB_FN (bb, fun)
/* Skip blocks that are being optimized for size, since our
transformation always increases code size. */
if (optimize_bb_for_size_p (bb))
/* Collect dead call candidates. */
for (i = gsi_start_bb (bb); !gsi_end_p (i); gsi_next (&i))
gcall *stmt = dyn_cast <gcall *> (gsi_stmt (i));
if (stmt
&& gimple_call_builtin_p (stmt, BUILT_IN_NORMAL)
&& (gimple_call_lhs (stmt)
? can_use_internal_fn (stmt)
: can_test_argument_range (stmt))
&& can_guard_call_p (stmt))
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "Found conditional dead call: ");
print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
fprintf (dump_file, "\n");
if (!cond_dead_built_in_calls.exists ())
cond_dead_built_in_calls.create (64);
cond_dead_built_in_calls.safe_push (stmt);
if (!cond_dead_built_in_calls.exists ())
return 0;
shrink_wrap_conditional_dead_built_in_calls (cond_dead_built_in_calls);
free_dominance_info (CDI_POST_DOMINATORS);
/* As we introduced new control-flow we need to insert PHI-nodes
for the call-clobbers of the remaining call. */
mark_virtual_operands_for_renaming (fun);
return TODO_update_ssa;
} // anon namespace
gimple_opt_pass *
make_pass_call_cdce (gcc::context *ctxt)
return new pass_call_cdce (ctxt);