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tree-ssa-copy.c (cached_last_copy_of): Remove.

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2010-08-07  Richard Guenther  <rguenther@suse.de>

	* tree-ssa-copy.c (cached_last_copy_of): Remove.
	(valueize_val): New function.
	(get_last_copy_of): Remove.
	(set_copy_of_val): Simplify.
	(dump_copy_of): Likewise.
	(copy_prop_visit_cond_stmt): Use valueize_val.
	(copy_prop_visit_phi_node): Properly handle unvisited names.
	Drop code managing copy-of chains.
	(init_copy_prop): Adjust.
	(fini_copy_prop): Likewise.
	(execute_copy_prop): Remove obsolete comment.

From-SVN: r163032
This commit is contained in:
Richard Guenther 2010-08-09 13:20:11 +00:00 • committed by Richard Biener
parent 37609bf086
commit ec64af64d6
2 changed files with 68 additions and 214 deletions
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14
gcc/ChangeLog
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@ -1,3 +1,17 @@
2010-08-09 Richard Guenther <rguenther@suse.de>
* tree-ssa-copy.c (cached_last_copy_of): Remove.
(valueize_val): New function.
(get_last_copy_of): Remove.
(set_copy_of_val): Simplify.
(dump_copy_of): Likewise.
(copy_prop_visit_cond_stmt): Use valueize_val.
(copy_prop_visit_phi_node): Properly handle unvisited names.
Drop code managing copy-of chains.
(init_copy_prop): Adjust.
(fini_copy_prop): Likewise.
(execute_copy_prop): Remove obsolete comment.
2010-08-09 Richard Guenther <rguenther@suse.de>
PR middle-end/44632

268
gcc/tree-ssa-copy.c
View file

@ -274,31 +274,23 @@ propagate_tree_value_into_stmt (gimple_stmt_iterator *gsi, tree val)
/*---------------------------------------------------------------------------
Copy propagation
---------------------------------------------------------------------------*/
/* During propagation, we keep chains of variables that are copies of
one another. If variable X_i is a copy of X_j and X_j is a copy of
X_k, COPY_OF will contain:
/* Lattice for copy-propagation. The lattice is initialized to
UNDEFINED (value == NULL) for SSA names that can become a copy
of something or VARYING (value == self) if not (see get_copy_of_val
and stmt_may_generate_copy). Other values make the name a COPY
of that value.
COPY_OF[i].VALUE = X_j
COPY_OF[j].VALUE = X_k
COPY_OF[k].VALUE = X_k
After propagation, the copy-of value for each variable X_i is
converted into the final value by walking the copy-of chains and
updating COPY_OF[i].VALUE to be the last element of the chain. */
When visiting a statement or PHI node the lattice value for an
SSA name can transition from UNDEFINED to COPY to VARYING. */
struct prop_value_d {
/* Copy-of value. */
tree value;
};
typedef struct prop_value_d prop_value_t;
static prop_value_t *copy_of;
/* Used in set_copy_of_val to determine if the last link of a copy-of
chain has changed. */
static tree *cached_last_copy_of;
/* Return true if this statement may generate a useful copy. */
@ -346,82 +338,38 @@ get_copy_of_val (tree var)
return val;
}
/* Return the variable VAR is a copy of or VAR if VAR isn't the result
of a copy. */
/* Return last link in the copy-of chain for VAR. */
static tree
get_last_copy_of (tree var)
static inline tree
valueize_val (tree var)
{
tree last;
int i;
/* Traverse COPY_OF starting at VAR until we get to the last
link in the chain. Since it is possible to have cycles in PHI
nodes, the copy-of chain may also contain cycles.
To avoid infinite loops and to avoid traversing lengthy copy-of
chains, we artificially limit the maximum number of chains we are
willing to traverse.
The value 5 was taken from a compiler and runtime library
bootstrap and a mixture of C and C++ code from various sources.
More than 82% of all copy-of chains were shorter than 5 links. */
#define LIMIT 5
last = var;
for (i = 0; i < LIMIT; i++)
if (TREE_CODE (var) == SSA_NAME)
{
tree copy = copy_of[SSA_NAME_VERSION (last)].value;
if (copy == NULL_TREE || copy == last)
break;
last = copy;
tree val = get_copy_of_val (var)->value;
if (val)
return val;
}
/* If we have reached the limit, then we are either in a copy-of
cycle or the copy-of chain is too long. In this case, just
return VAR so that it is not considered a copy of anything. */
return (i < LIMIT ? last : var);
return var;
}
/* Set FIRST to be the first variable in the copy-of chain for DEST.
If DEST's copy-of value or its copy-of chain has changed, return
true.
MEM_REF is the memory reference where FIRST is stored. This is
used when DEST is a non-register and we are copy propagating loads
and stores. */
/* Set VAL to be the copy of VAR. If that changed return true. */
static inline bool
set_copy_of_val (tree dest, tree first)
set_copy_of_val (tree var, tree val)
{
unsigned int dest_ver = SSA_NAME_VERSION (dest);
tree old_first, old_last, new_last;
unsigned int ver = SSA_NAME_VERSION (var);
tree old;
/* Set FIRST to be the first link in COPY_OF[DEST]. If that
changed, return true. */
old_first = copy_of[dest_ver].value;
copy_of[dest_ver].value = first;
old = copy_of[ver].value;
copy_of[ver].value = val;
if (old_first != first)
if (old != val)
return true;
/* If FIRST and OLD_FIRST are the same, we need to check whether the
copy-of chain starting at FIRST ends in a different variable. If
the copy-of chain starting at FIRST ends up in a different
variable than the last cached value we had for DEST, then return
true because DEST is now a copy of a different variable.
This test is necessary because even though the first link in the
copy-of chain may not have changed, if any of the variables in
the copy-of chain changed its final value, DEST will now be the
copy of a different variable, so we have to do another round of
propagation for everything that depends on DEST. */
old_last = cached_last_copy_of[dest_ver];
new_last = get_last_copy_of (dest);
cached_last_copy_of[dest_ver] = new_last;
return (old_last != new_last);
return false;
}
@ -431,50 +379,31 @@ static void
dump_copy_of (FILE *file, tree var)
{
tree val;
sbitmap visited;
print_generic_expr (file, var, dump_flags);
if (TREE_CODE (var) != SSA_NAME)
return;
visited = sbitmap_alloc (num_ssa_names);
sbitmap_zero (visited);
SET_BIT (visited, SSA_NAME_VERSION (var));
val = copy_of[SSA_NAME_VERSION (var)].value;
fprintf (file, " copy-of chain: ");
val = var;
print_generic_expr (file, val, 0);
print_generic_expr (file, var, 0);
fprintf (file, " ");
while (copy_of[SSA_NAME_VERSION (val)].value)
if (!val)
fprintf (file, "[UNDEFINED]");
else if (val == var)
fprintf (file, "[NOT A COPY]");
else
{
fprintf (file, "-> ");
val = copy_of[SSA_NAME_VERSION (val)].value;
print_generic_expr (file, val, 0);
fprintf (file, " ");
if (TEST_BIT (visited, SSA_NAME_VERSION (val)))
break;
SET_BIT (visited, SSA_NAME_VERSION (val));
fprintf (file, "[COPY]");
}
val = get_copy_of_val (var)->value;
if (val == NULL_TREE)
fprintf (file, "[UNDEFINED]");
else if (val != var)
fprintf (file, "[COPY]");
else
fprintf (file, "[NOT A COPY]");
sbitmap_free (visited);
}
/* Evaluate the RHS of STMT. If it produces a valid copy, set the LHS
value and store the LHS into *RESULT_P. If STMT generates more
than one name (i.e., STMT is an aliased store), it is enough to
store the first name in the VDEF list into *RESULT_P. After
all, the names generated will be VUSEd in the same statements. */
value and store the LHS into *RESULT_P. */
static enum ssa_prop_result
copy_prop_visit_assignment (gimple stmt, tree *result_p)
@ -485,7 +414,6 @@ copy_prop_visit_assignment (gimple stmt, tree *result_p)
lhs = gimple_assign_lhs (stmt);
rhs = gimple_assign_rhs1 (stmt);
gcc_assert (gimple_assign_rhs_code (stmt) == SSA_NAME);
rhs_val = get_copy_of_val (rhs);
@ -531,8 +459,8 @@ copy_prop_visit_cond_stmt (gimple stmt, edge *taken_edge_p)
are predicates involving two SSA_NAMEs. */
if (TREE_CODE (op0) == SSA_NAME && TREE_CODE (op1) == SSA_NAME)
{
op0 = get_last_copy_of (op0);
op1 = get_last_copy_of (op1);
op0 = valueize_val (op0);
op1 = valueize_val (op1);
/* See if we can determine the predicate's value. */
if (dump_file && (dump_flags & TDF_DETAILS))
@ -642,7 +570,6 @@ copy_prop_visit_phi_node (gimple phi)
{
fprintf (dump_file, "\nVisiting PHI node: ");
print_gimple_stmt (dump_file, phi, 0, dump_flags);
fprintf (dump_file, "\n\n");
}
for (i = 0; i < gimple_phi_num_args (phi); i++)
@ -670,7 +597,8 @@ copy_prop_visit_phi_node (gimple phi)
their loops and prevent coalescing opportunities. If the
value was loop invariant, it will be hoisted by LICM and
exposed for copy propagation. Not a problem for virtual
operands though. */
operands though.
??? The value will be always loop invariant. */
if (is_gimple_reg (lhs)
&& loop_depth_of_name (arg) > loop_depth_of_name (lhs))
{
@ -678,11 +606,6 @@ copy_prop_visit_phi_node (gimple phi)
break;
}
/* If the LHS appears in the argument list, ignore it. It is
irrelevant as a copy. */
if (arg == lhs || get_last_copy_of (arg) == lhs)
continue;
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "\tArgument #%d: ", i);
@ -692,30 +615,31 @@ copy_prop_visit_phi_node (gimple phi)
arg_val = get_copy_of_val (arg);
/* If we didn't visit the definition of arg yet treat it as
UNDEFINED. This also handles PHI arguments that are the
same as lhs. We'll come here again. */
if (!arg_val->value)
continue;
/* If the LHS didn't have a value yet, make it a copy of the
first argument we find. Notice that while we make the LHS be
a copy of the argument itself, we take the memory reference
from the argument's value so that we can compare it to the
memory reference of all the other arguments. */
first argument we find. */
if (phi_val.value == NULL_TREE)
{
phi_val.value = arg_val->value ? arg_val->value : arg;
phi_val.value = arg_val->value;
continue;
}
/* If PHI_VAL and ARG don't have a common copy-of chain, then
this PHI node cannot be a copy operation. Also, if we are
copy propagating stores and these two arguments came from
different memory references, they cannot be considered
copies. */
if (get_last_copy_of (phi_val.value) != get_last_copy_of (arg))
this PHI node cannot be a copy operation. */
if (phi_val.value != arg_val->value)
{
phi_val.value = lhs;
break;
}
}
if (phi_val.value && may_propagate_copy (lhs, phi_val.value)
if (phi_val.value
&& may_propagate_copy (lhs, phi_val.value)
&& set_copy_of_val (lhs, phi_val.value))
retval = (phi_val.value != lhs) ? SSA_PROP_INTERESTING : SSA_PROP_VARYING;
else
@ -723,7 +647,7 @@ copy_prop_visit_phi_node (gimple phi)
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "\nPHI node ");
fprintf (dump_file, "PHI node ");
dump_copy_of (dump_file, lhs);
fprintf (dump_file, "\nTelling the propagator to ");
if (retval == SSA_PROP_INTERESTING)
@ -739,9 +663,7 @@ copy_prop_visit_phi_node (gimple phi)
}
/* Initialize structures used for copy propagation. PHIS_ONLY is true
if we should only consider PHI nodes as generating copy propagation
opportunities. */
/* Initialize structures used for copy propagation. */
static void
init_copy_prop (void)
@ -750,8 +672,6 @@ init_copy_prop (void)
copy_of = XCNEWVEC (prop_value_t, num_ssa_names);
cached_last_copy_of = XCNEWVEC (tree, num_ssa_names);
FOR_EACH_BB (bb)
{
gimple_stmt_iterator si;
@ -773,7 +693,8 @@ init_copy_prop (void)
Otherwise, this may move loop variant variables outside of
their loops and prevent coalescing opportunities. If the
value was loop invariant, it will be hoisted by LICM and
exposed for copy propagation. */
exposed for copy propagation.
??? This doesn't make sense. */
if (stmt_ends_bb_p (stmt))
prop_set_simulate_again (stmt, true);
else if (stmt_may_generate_copy (stmt)
@ -790,8 +711,6 @@ init_copy_prop (void)
FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
if (!prop_simulate_again_p (stmt))
set_copy_of_val (def, def);
else
cached_last_copy_of[SSA_NAME_VERSION (def)] = def;
}
/* In loop-closed SSA form do not copy-propagate through
@ -820,8 +739,6 @@ init_copy_prop (void)
if (!prop_simulate_again_p (phi))
set_copy_of_val (def, def);
else
cached_last_copy_of[SSA_NAME_VERSION (def)] = def;
}
}
}
@ -855,8 +772,6 @@ fini_copy_prop (void)
|| copy_of[i].value == var)
continue;
copy_of[i].value = get_last_copy_of (var);
/* In theory the points-to solution of all members of the
copy chain is their intersection. For now we do not bother
to compute this but only make sure we do not lose points-to
@ -872,7 +787,6 @@ fini_copy_prop (void)
substitute_and_fold (get_value, NULL, true);
free (cached_last_copy_of);
free (copy_of);
}
@ -908,81 +822,7 @@ fini_copy_prop (void)
through edges marked executable by the propagation engine. So,
when visiting statement #2 for the first time, we will only look at
the first argument (a_24) and optimistically assume that its value
is the copy of a_24 (x_1).
The problem with this approach is that it may fail to discover copy
relations in PHI cycles. Instead of propagating copy-of
values, we actually propagate copy-of chains. For instance:
A_3 = B_1;
C_9 = A_3;
D_4 = C_9;
X_i = D_4;
In this code fragment, COPY-OF (X_i) = { D_4, C_9, A_3, B_1 }.
Obviously, we are only really interested in the last value of the
chain, however the propagator needs to access the copy-of chain
when visiting PHI nodes.
To represent the copy-of chain, we use the array COPY_CHAINS, which
holds the first link in the copy-of chain for every variable.
If variable X_i is a copy of X_j, which in turn is a copy of X_k,
the array will contain:
COPY_CHAINS[i] = X_j
COPY_CHAINS[j] = X_k
COPY_CHAINS[k] = X_k
Keeping copy-of chains instead of copy-of values directly becomes
important when visiting PHI nodes. Suppose that we had the
following PHI cycle, such that x_52 is already considered a copy of
x_53:
1 x_54 = PHI <x_53, x_52>
2 x_53 = PHI <x_898, x_54>
Visit #1: x_54 is copy-of x_53 (because x_52 is copy-of x_53)
Visit #2: x_53 is copy-of x_898 (because x_54 is a copy of x_53,
so it is considered irrelevant
as a copy).
Visit #1: x_54 is copy-of nothing (x_53 is a copy-of x_898 and
x_52 is a copy of x_53, so
they don't match)
Visit #2: x_53 is copy-of nothing
This problem is avoided by keeping a chain of copies, instead of
the final copy-of value. Propagation will now only keep the first
element of a variable's copy-of chain. When visiting PHI nodes,
arguments are considered equal if their copy-of chains end in the
same variable. So, as long as their copy-of chains overlap, we
know that they will be a copy of the same variable, regardless of
which variable that may be).
Propagation would then proceed as follows (the notation a -> b
means that a is a copy-of b):
Visit #1: x_54 = PHI <x_53, x_52>
x_53 -> x_53
x_52 -> x_53
Result: x_54 -> x_53. Value changed. Add SSA edges.
Visit #1: x_53 = PHI <x_898, x_54>
x_898 -> x_898
x_54 -> x_53
Result: x_53 -> x_898. Value changed. Add SSA edges.
Visit #2: x_54 = PHI <x_53, x_52>
x_53 -> x_898
x_52 -> x_53 -> x_898
Result: x_54 -> x_898. Value changed. Add SSA edges.
Visit #2: x_53 = PHI <x_898, x_54>
x_898 -> x_898
x_54 -> x_898
Result: x_53 -> x_898. Value didn't change. Stable state
Once the propagator stabilizes, we end up with the desired result
x_53 and x_54 are both copies of x_898. */
is the copy of a_24 (x_1). */
static unsigned int
execute_copy_prop (void)