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tree-predcom.c
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tree-predcom.c
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/* Predictive commoning.
Copyright (C) 2005, 2007, 2008, 2009, 2010
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/>. */
/* This file implements the predictive commoning optimization. Predictive
commoning can be viewed as CSE around a loop, and with some improvements,
as generalized strength reduction-- i.e., reusing values computed in
earlier iterations of a loop in the later ones. So far, the pass only
handles the most useful case, that is, reusing values of memory references.
If you think this is all just a special case of PRE, you are sort of right;
however, concentrating on loops is simpler, and makes it possible to
incorporate data dependence analysis to detect the opportunities, perform
loop unrolling to avoid copies together with renaming immediately,
and if needed, we could also take register pressure into account.
Let us demonstrate what is done on an example:
for (i = 0; i < 100; i++)
{
a[i+2] = a[i] + a[i+1];
b[10] = b[10] + i;
c[i] = c[99 - i];
d[i] = d[i + 1];
}
1) We find data references in the loop, and split them to mutually
independent groups (i.e., we find components of a data dependence
graph). We ignore read-read dependences whose distance is not constant.
(TODO -- we could also ignore antidependences). In this example, we
find the following groups:
a[i]{read}, a[i+1]{read}, a[i+2]{write}
b[10]{read}, b[10]{write}
c[99 - i]{read}, c[i]{write}
d[i + 1]{read}, d[i]{write}
2) Inside each of the group, we verify several conditions:
a) all the references must differ in indices only, and the indices
must all have the same step
b) the references must dominate loop latch (and thus, they must be
ordered by dominance relation).
c) the distance of the indices must be a small multiple of the step
We are then able to compute the difference of the references (# of
iterations before they point to the same place as the first of them).
Also, in case there are writes in the loop, we split the groups into
chains whose head is the write whose values are used by the reads in
the same chain. The chains are then processed independently,
making the further transformations simpler. Also, the shorter chains
need the same number of registers, but may require lower unrolling
factor in order to get rid of the copies on the loop latch.
In our example, we get the following chains (the chain for c is invalid).
a[i]{read,+0}, a[i+1]{read,-1}, a[i+2]{write,-2}
b[10]{read,+0}, b[10]{write,+0}
d[i + 1]{read,+0}, d[i]{write,+1}
3) For each read, we determine the read or write whose value it reuses,
together with the distance of this reuse. I.e. we take the last
reference before it with distance 0, or the last of the references
with the smallest positive distance to the read. Then, we remove
the references that are not used in any of these chains, discard the
empty groups, and propagate all the links so that they point to the
single root reference of the chain (adjusting their distance
appropriately). Some extra care needs to be taken for references with
step 0. In our example (the numbers indicate the distance of the
reuse),
a[i] --> (*) 2, a[i+1] --> (*) 1, a[i+2] (*)
b[10] --> (*) 1, b[10] (*)
4) The chains are combined together if possible. If the corresponding
elements of two chains are always combined together with the same
operator, we remember just the result of this combination, instead
of remembering the values separately. We may need to perform
reassociation to enable combining, for example
e[i] + f[i+1] + e[i+1] + f[i]
can be reassociated as
(e[i] + f[i]) + (e[i+1] + f[i+1])
and we can combine the chains for e and f into one chain.
5) For each root reference (end of the chain) R, let N be maximum distance
of a reference reusing its value. Variables R0 upto RN are created,
together with phi nodes that transfer values from R1 .. RN to
R0 .. R(N-1).
Initial values are loaded to R0..R(N-1) (in case not all references
must necessarily be accessed and they may trap, we may fail here;
TODO sometimes, the loads could be guarded by a check for the number
of iterations). Values loaded/stored in roots are also copied to
RN. Other reads are replaced with the appropriate variable Ri.
Everything is put to SSA form.
As a small improvement, if R0 is dead after the root (i.e., all uses of
the value with the maximum distance dominate the root), we can avoid
creating RN and use R0 instead of it.
In our example, we get (only the parts concerning a and b are shown):
for (i = 0; i < 100; i++)
{
f = phi (a[0], s);
s = phi (a[1], f);
x = phi (b[10], x);
f = f + s;
a[i+2] = f;
x = x + i;
b[10] = x;
}
6) Factor F for unrolling is determined as the smallest common multiple of
(N + 1) for each root reference (N for references for that we avoided
creating RN). If F and the loop is small enough, loop is unrolled F
times. The stores to RN (R0) in the copies of the loop body are
periodically replaced with R0, R1, ... (R1, R2, ...), so that they can
be coalesced and the copies can be eliminated.
TODO -- copy propagation and other optimizations may change the live
ranges of the temporary registers and prevent them from being coalesced;
this may increase the register pressure.
In our case, F = 2 and the (main loop of the) result is
for (i = 0; i < ...; i += 2)
{
f = phi (a[0], f);
s = phi (a[1], s);
x = phi (b[10], x);
f = f + s;
a[i+2] = f;
x = x + i;
b[10] = x;
s = s + f;
a[i+3] = s;
x = x + i;
b[10] = x;
}
TODO -- stores killing other stores can be taken into account, e.g.,
for (i = 0; i < n; i++)
{
a[i] = 1;
a[i+2] = 2;
}
can be replaced with
t0 = a[0];
t1 = a[1];
for (i = 0; i < n; i++)
{
a[i] = 1;
t2 = 2;
t0 = t1;
t1 = t2;
}
a[n] = t0;
a[n+1] = t1;
The interesting part is that this would generalize store motion; still, since
sm is performed elsewhere, it does not seem that important.
Predictive commoning can be generalized for arbitrary computations (not
just memory loads), and also nontrivial transfer functions (e.g., replacing
i * i with ii_last + 2 * i + 1), to generalize strength reduction. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "tm_p.h"
#include "cfgloop.h"
#include "tree-flow.h"
#include "ggc.h"
#include "tree-data-ref.h"
#include "tree-scalar-evolution.h"
#include "tree-chrec.h"
#include "params.h"
#include "diagnostic.h"
#include "tree-pass.h"
#include "tree-affine.h"
#include "tree-inline.h"
/* The maximum number of iterations between the considered memory
references. */
#define MAX_DISTANCE (target_avail_regs < 16 ? 4 : 8)
/* Data references (or phi nodes that carry data reference values across
loop iterations). */
typedef struct dref_d
{
/* The reference itself. */
struct data_reference *ref;
/* The statement in that the reference appears. */
gimple stmt;
/* In case that STMT is a phi node, this field is set to the SSA name
defined by it in replace_phis_by_defined_names (in order to avoid
pointing to phi node that got reallocated in the meantime). */
tree name_defined_by_phi;
/* Distance of the reference from the root of the chain (in number of
iterations of the loop). */
unsigned distance;
/* Number of iterations offset from the first reference in the component. */
double_int offset;
/* Number of the reference in a component, in dominance ordering. */
unsigned pos;
/* True if the memory reference is always accessed when the loop is
entered. */
unsigned always_accessed : 1;
} *dref;
DEF_VEC_P (dref);
DEF_VEC_ALLOC_P (dref, heap);
/* Type of the chain of the references. */
enum chain_type
{
/* The addresses of the references in the chain are constant. */
CT_INVARIANT,
/* There are only loads in the chain. */
CT_LOAD,
/* Root of the chain is store, the rest are loads. */
CT_STORE_LOAD,
/* A combination of two chains. */
CT_COMBINATION
};
/* Chains of data references. */
typedef struct chain
{
/* Type of the chain. */
enum chain_type type;
/* For combination chains, the operator and the two chains that are
combined, and the type of the result. */
enum tree_code op;
tree rslt_type;
struct chain *ch1, *ch2;
/* The references in the chain. */
VEC(dref,heap) *refs;
/* The maximum distance of the reference in the chain from the root. */
unsigned length;
/* The variables used to copy the value throughout iterations. */
VEC(tree,heap) *vars;
/* Initializers for the variables. */
VEC(tree,heap) *inits;
/* True if there is a use of a variable with the maximal distance
that comes after the root in the loop. */
unsigned has_max_use_after : 1;
/* True if all the memory references in the chain are always accessed. */
unsigned all_always_accessed : 1;
/* True if this chain was combined together with some other chain. */
unsigned combined : 1;
} *chain_p;
DEF_VEC_P (chain_p);
DEF_VEC_ALLOC_P (chain_p, heap);
/* Describes the knowledge about the step of the memory references in
the component. */
enum ref_step_type
{
/* The step is zero. */
RS_INVARIANT,
/* The step is nonzero. */
RS_NONZERO,
/* The step may or may not be nonzero. */
RS_ANY
};
/* Components of the data dependence graph. */
struct component
{
/* The references in the component. */
VEC(dref,heap) *refs;
/* What we know about the step of the references in the component. */
enum ref_step_type comp_step;
/* Next component in the list. */
struct component *next;
};
/* Bitmap of ssa names defined by looparound phi nodes covered by chains. */
static bitmap looparound_phis;
/* Cache used by tree_to_aff_combination_expand. */
static struct pointer_map_t *name_expansions;
/* Dumps data reference REF to FILE. */
extern void dump_dref (FILE *, dref);
void
dump_dref (FILE *file, dref ref)
{
if (ref->ref)
{
fprintf (file, " ");
print_generic_expr (file, DR_REF (ref->ref), TDF_SLIM);
fprintf (file, " (id %u%s)\n", ref->pos,
DR_IS_READ (ref->ref) ? "" : ", write");
fprintf (file, " offset ");
dump_double_int (file, ref->offset, false);
fprintf (file, "\n");
fprintf (file, " distance %u\n", ref->distance);
}
else
{
if (gimple_code (ref->stmt) == GIMPLE_PHI)
fprintf (file, " looparound ref\n");
else
fprintf (file, " combination ref\n");
fprintf (file, " in statement ");
print_gimple_stmt (file, ref->stmt, 0, TDF_SLIM);
fprintf (file, "\n");
fprintf (file, " distance %u\n", ref->distance);
}
}
/* Dumps CHAIN to FILE. */
extern void dump_chain (FILE *, chain_p);
void
dump_chain (FILE *file, chain_p chain)
{
dref a;
const char *chain_type;
unsigned i;
tree var;
switch (chain->type)
{
case CT_INVARIANT:
chain_type = "Load motion";
break;
case CT_LOAD:
chain_type = "Loads-only";
break;
case CT_STORE_LOAD:
chain_type = "Store-loads";
break;
case CT_COMBINATION:
chain_type = "Combination";
break;
default:
gcc_unreachable ();
}
fprintf (file, "%s chain %p%s\n", chain_type, (void *) chain,
chain->combined ? " (combined)" : "");
if (chain->type != CT_INVARIANT)
fprintf (file, " max distance %u%s\n", chain->length,
chain->has_max_use_after ? "" : ", may reuse first");
if (chain->type == CT_COMBINATION)
{
fprintf (file, " equal to %p %s %p in type ",
(void *) chain->ch1, op_symbol_code (chain->op),
(void *) chain->ch2);
print_generic_expr (file, chain->rslt_type, TDF_SLIM);
fprintf (file, "\n");
}
if (chain->vars)
{
fprintf (file, " vars");
for (i = 0; VEC_iterate (tree, chain->vars, i, var); i++)
{
fprintf (file, " ");
print_generic_expr (file, var, TDF_SLIM);
}
fprintf (file, "\n");
}
if (chain->inits)
{
fprintf (file, " inits");
for (i = 0; VEC_iterate (tree, chain->inits, i, var); i++)
{
fprintf (file, " ");
print_generic_expr (file, var, TDF_SLIM);
}
fprintf (file, "\n");
}
fprintf (file, " references:\n");
for (i = 0; VEC_iterate (dref, chain->refs, i, a); i++)
dump_dref (file, a);
fprintf (file, "\n");
}
/* Dumps CHAINS to FILE. */
extern void dump_chains (FILE *, VEC (chain_p, heap) *);
void
dump_chains (FILE *file, VEC (chain_p, heap) *chains)
{
chain_p chain;
unsigned i;
for (i = 0; VEC_iterate (chain_p, chains, i, chain); i++)
dump_chain (file, chain);
}
/* Dumps COMP to FILE. */
extern void dump_component (FILE *, struct component *);
void
dump_component (FILE *file, struct component *comp)
{
dref a;
unsigned i;
fprintf (file, "Component%s:\n",
comp->comp_step == RS_INVARIANT ? " (invariant)" : "");
for (i = 0; VEC_iterate (dref, comp->refs, i, a); i++)
dump_dref (file, a);
fprintf (file, "\n");
}
/* Dumps COMPS to FILE. */
extern void dump_components (FILE *, struct component *);
void
dump_components (FILE *file, struct component *comps)
{
struct component *comp;
for (comp = comps; comp; comp = comp->next)
dump_component (file, comp);
}
/* Frees a chain CHAIN. */
static void
release_chain (chain_p chain)
{
dref ref;
unsigned i;
if (chain == NULL)
return;
for (i = 0; VEC_iterate (dref, chain->refs, i, ref); i++)
free (ref);
VEC_free (dref, heap, chain->refs);
VEC_free (tree, heap, chain->vars);
VEC_free (tree, heap, chain->inits);
free (chain);
}
/* Frees CHAINS. */
static void
release_chains (VEC (chain_p, heap) *chains)
{
unsigned i;
chain_p chain;
for (i = 0; VEC_iterate (chain_p, chains, i, chain); i++)
release_chain (chain);
VEC_free (chain_p, heap, chains);
}
/* Frees a component COMP. */
static void
release_component (struct component *comp)
{
VEC_free (dref, heap, comp->refs);
free (comp);
}
/* Frees list of components COMPS. */
static void
release_components (struct component *comps)
{
struct component *act, *next;
for (act = comps; act; act = next)
{
next = act->next;
release_component (act);
}
}
/* Finds a root of tree given by FATHERS containing A, and performs path
shortening. */
static unsigned
component_of (unsigned fathers[], unsigned a)
{
unsigned root, n;
for (root = a; root != fathers[root]; root = fathers[root])
continue;
for (; a != root; a = n)
{
n = fathers[a];
fathers[a] = root;
}
return root;
}
/* Join operation for DFU. FATHERS gives the tree, SIZES are sizes of the
components, A and B are components to merge. */
static void
merge_comps (unsigned fathers[], unsigned sizes[], unsigned a, unsigned b)
{
unsigned ca = component_of (fathers, a);
unsigned cb = component_of (fathers, b);
if (ca == cb)
return;
if (sizes[ca] < sizes[cb])
{
sizes[cb] += sizes[ca];
fathers[ca] = cb;
}
else
{
sizes[ca] += sizes[cb];
fathers[cb] = ca;
}
}
/* Returns true if A is a reference that is suitable for predictive commoning
in the innermost loop that contains it. REF_STEP is set according to the
step of the reference A. */
static bool
suitable_reference_p (struct data_reference *a, enum ref_step_type *ref_step)
{
tree ref = DR_REF (a), step = DR_STEP (a);
if (!step
|| !is_gimple_reg_type (TREE_TYPE (ref))
|| tree_could_throw_p (ref))
return false;
if (integer_zerop (step))
*ref_step = RS_INVARIANT;
else if (integer_nonzerop (step))
*ref_step = RS_NONZERO;
else
*ref_step = RS_ANY;
return true;
}
/* Stores DR_OFFSET (DR) + DR_INIT (DR) to OFFSET. */
static void
aff_combination_dr_offset (struct data_reference *dr, aff_tree *offset)
{
aff_tree delta;
tree_to_aff_combination_expand (DR_OFFSET (dr), sizetype, offset,
&name_expansions);
aff_combination_const (&delta, sizetype, tree_to_double_int (DR_INIT (dr)));
aff_combination_add (offset, &delta);
}
/* Determines number of iterations of the innermost enclosing loop before B
refers to exactly the same location as A and stores it to OFF. If A and
B do not have the same step, they never meet, or anything else fails,
returns false, otherwise returns true. Both A and B are assumed to
satisfy suitable_reference_p. */
static bool
determine_offset (struct data_reference *a, struct data_reference *b,
double_int *off)
{
aff_tree diff, baseb, step;
tree typea, typeb;
/* Check that both the references access the location in the same type. */
typea = TREE_TYPE (DR_REF (a));
typeb = TREE_TYPE (DR_REF (b));
if (!useless_type_conversion_p (typeb, typea))
return false;
/* Check whether the base address and the step of both references is the
same. */
if (!operand_equal_p (DR_STEP (a), DR_STEP (b), 0)
|| !operand_equal_p (DR_BASE_ADDRESS (a), DR_BASE_ADDRESS (b), 0))
return false;
if (integer_zerop (DR_STEP (a)))
{
/* If the references have loop invariant address, check that they access
exactly the same location. */
*off = double_int_zero;
return (operand_equal_p (DR_OFFSET (a), DR_OFFSET (b), 0)
&& operand_equal_p (DR_INIT (a), DR_INIT (b), 0));
}
/* Compare the offsets of the addresses, and check whether the difference
is a multiple of step. */
aff_combination_dr_offset (a, &diff);
aff_combination_dr_offset (b, &baseb);
aff_combination_scale (&baseb, double_int_minus_one);
aff_combination_add (&diff, &baseb);
tree_to_aff_combination_expand (DR_STEP (a), sizetype,
&step, &name_expansions);
return aff_combination_constant_multiple_p (&diff, &step, off);
}
/* Returns the last basic block in LOOP for that we are sure that
it is executed whenever the loop is entered. */
static basic_block
last_always_executed_block (struct loop *loop)
{
unsigned i;
VEC (edge, heap) *exits = get_loop_exit_edges (loop);
edge ex;
basic_block last = loop->latch;
for (i = 0; VEC_iterate (edge, exits, i, ex); i++)
last = nearest_common_dominator (CDI_DOMINATORS, last, ex->src);
VEC_free (edge, heap, exits);
return last;
}
/* Splits dependence graph on DATAREFS described by DEPENDS to components. */
static struct component *
split_data_refs_to_components (struct loop *loop,
VEC (data_reference_p, heap) *datarefs,
VEC (ddr_p, heap) *depends)
{
unsigned i, n = VEC_length (data_reference_p, datarefs);
unsigned ca, ia, ib, bad;
unsigned *comp_father = XNEWVEC (unsigned, n + 1);
unsigned *comp_size = XNEWVEC (unsigned, n + 1);
struct component **comps;
struct data_reference *dr, *dra, *drb;
struct data_dependence_relation *ddr;
struct component *comp_list = NULL, *comp;
dref dataref;
basic_block last_always_executed = last_always_executed_block (loop);
for (i = 0; VEC_iterate (data_reference_p, datarefs, i, dr); i++)
{
if (!DR_REF (dr))
{
/* A fake reference for call or asm_expr that may clobber memory;
just fail. */
goto end;
}
dr->aux = (void *) (size_t) i;
comp_father[i] = i;
comp_size[i] = 1;
}
/* A component reserved for the "bad" data references. */
comp_father[n] = n;
comp_size[n] = 1;
for (i = 0; VEC_iterate (data_reference_p, datarefs, i, dr); i++)
{
enum ref_step_type dummy;
if (!suitable_reference_p (dr, &dummy))
{
ia = (unsigned) (size_t) dr->aux;
merge_comps (comp_father, comp_size, n, ia);
}
}
for (i = 0; VEC_iterate (ddr_p, depends, i, ddr); i++)
{
double_int dummy_off;
if (DDR_ARE_DEPENDENT (ddr) == chrec_known)
continue;
dra = DDR_A (ddr);
drb = DDR_B (ddr);
ia = component_of (comp_father, (unsigned) (size_t) dra->aux);
ib = component_of (comp_father, (unsigned) (size_t) drb->aux);
if (ia == ib)
continue;
bad = component_of (comp_father, n);
/* If both A and B are reads, we may ignore unsuitable dependences. */
if (DR_IS_READ (dra) && DR_IS_READ (drb)
&& (ia == bad || ib == bad
|| !determine_offset (dra, drb, &dummy_off)))
continue;
merge_comps (comp_father, comp_size, ia, ib);
}
comps = XCNEWVEC (struct component *, n);
bad = component_of (comp_father, n);
for (i = 0; VEC_iterate (data_reference_p, datarefs, i, dr); i++)
{
ia = (unsigned) (size_t) dr->aux;
ca = component_of (comp_father, ia);
if (ca == bad)
continue;
comp = comps[ca];
if (!comp)
{
comp = XCNEW (struct component);
comp->refs = VEC_alloc (dref, heap, comp_size[ca]);
comps[ca] = comp;
}
dataref = XCNEW (struct dref_d);
dataref->ref = dr;
dataref->stmt = DR_STMT (dr);
dataref->offset = double_int_zero;
dataref->distance = 0;
dataref->always_accessed
= dominated_by_p (CDI_DOMINATORS, last_always_executed,
gimple_bb (dataref->stmt));
dataref->pos = VEC_length (dref, comp->refs);
VEC_quick_push (dref, comp->refs, dataref);
}
for (i = 0; i < n; i++)
{
comp = comps[i];
if (comp)
{
comp->next = comp_list;
comp_list = comp;
}
}
free (comps);
end:
free (comp_father);
free (comp_size);
return comp_list;
}
/* Returns true if the component COMP satisfies the conditions
described in 2) at the beginning of this file. LOOP is the current
loop. */
static bool
suitable_component_p (struct loop *loop, struct component *comp)
{
unsigned i;
dref a, first;
basic_block ba, bp = loop->header;
bool ok, has_write = false;
for (i = 0; VEC_iterate (dref, comp->refs, i, a); i++)
{
ba = gimple_bb (a->stmt);
if (!just_once_each_iteration_p (loop, ba))
return false;
gcc_assert (dominated_by_p (CDI_DOMINATORS, ba, bp));
bp = ba;
if (!DR_IS_READ (a->ref))
has_write = true;
}
first = VEC_index (dref, comp->refs, 0);
ok = suitable_reference_p (first->ref, &comp->comp_step);
gcc_assert (ok);
first->offset = double_int_zero;
for (i = 1; VEC_iterate (dref, comp->refs, i, a); i++)
{
if (!determine_offset (first->ref, a->ref, &a->offset))
return false;
#ifdef ENABLE_CHECKING
{
enum ref_step_type a_step;
ok = suitable_reference_p (a->ref, &a_step);
gcc_assert (ok && a_step == comp->comp_step);
}
#endif
}
/* If there is a write inside the component, we must know whether the
step is nonzero or not -- we would not otherwise be able to recognize
whether the value accessed by reads comes from the OFFSET-th iteration
or the previous one. */
if (has_write && comp->comp_step == RS_ANY)
return false;
return true;
}
/* Check the conditions on references inside each of components COMPS,
and remove the unsuitable components from the list. The new list
of components is returned. The conditions are described in 2) at
the beginning of this file. LOOP is the current loop. */
static struct component *
filter_suitable_components (struct loop *loop, struct component *comps)
{
struct component **comp, *act;
for (comp = &comps; *comp; )
{
act = *comp;
if (suitable_component_p (loop, act))
comp = &act->next;
else
{
dref ref;
unsigned i;
*comp = act->next;
for (i = 0; VEC_iterate (dref, act->refs, i, ref); i++)
free (ref);
release_component (act);
}
}
return comps;
}
/* Compares two drefs A and B by their offset and position. Callback for
qsort. */
static int
order_drefs (const void *a, const void *b)
{
const dref *const da = (const dref *) a;
const dref *const db = (const dref *) b;
int offcmp = double_int_scmp ((*da)->offset, (*db)->offset);
if (offcmp != 0)
return offcmp;
return (*da)->pos - (*db)->pos;
}
/* Returns root of the CHAIN. */
static inline dref
get_chain_root (chain_p chain)
{
return VEC_index (dref, chain->refs, 0);
}
/* Adds REF to the chain CHAIN. */
static void
add_ref_to_chain (chain_p chain, dref ref)
{
dref root = get_chain_root (chain);
double_int dist;
gcc_assert (double_int_scmp (root->offset, ref->offset) <= 0);
dist = double_int_add (ref->offset, double_int_neg (root->offset));
if (double_int_ucmp (uhwi_to_double_int (MAX_DISTANCE), dist) <= 0)
{
free (ref);
return;
}
gcc_assert (double_int_fits_in_uhwi_p (dist));
VEC_safe_push (dref, heap, chain->refs, ref);
ref->distance = double_int_to_uhwi (dist);
if (ref->distance >= chain->length)
{
chain->length = ref->distance;
chain->has_max_use_after = false;
}
if (ref->distance == chain->length
&& ref->pos > root->pos)
chain->has_max_use_after = true;
chain->all_always_accessed &= ref->always_accessed;
}
/* Returns the chain for invariant component COMP. */
static chain_p
make_invariant_chain (struct component *comp)
{
chain_p chain = XCNEW (struct chain);
unsigned i;
dref ref;
chain->type = CT_INVARIANT;
chain->all_always_accessed = true;
for (i = 0; VEC_iterate (dref, comp->refs, i, ref); i++)
{
VEC_safe_push (dref, heap, chain->refs, ref);
chain->all_always_accessed &= ref->always_accessed;
}
return chain;
}
/* Make a new chain rooted at REF. */
static chain_p
make_rooted_chain (dref ref)
{
chain_p chain = XCNEW (struct chain);
chain->type = DR_IS_READ (ref->ref) ? CT_LOAD : CT_STORE_LOAD;
VEC_safe_push (dref, heap, chain->refs, ref);
chain->all_always_accessed = ref->always_accessed;
ref->distance = 0;
return chain;
}
/* Returns true if CHAIN is not trivial. */
static bool
nontrivial_chain_p (chain_p chain)
{
return chain != NULL && VEC_length (dref, chain->refs) > 1;
}
/* Returns the ssa name that contains the value of REF, or NULL_TREE if there
is no such name. */