/* Copy propagation and SSA_NAME replacement support routines.
- Copyright (C) 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
+ Copyright (C) 2004, 2005, 2006, 2007, 2008, 2010
+ Free Software Foundation, Inc.
This file is part of GCC.
#include "tm.h"
#include "tree.h"
#include "flags.h"
-#include "rtl.h"
#include "tm_p.h"
-#include "ggc.h"
#include "basic-block.h"
#include "output.h"
#include "expr.h"
#include "function.h"
#include "diagnostic.h"
+#include "tree-pretty-print.h"
+#include "gimple-pretty-print.h"
#include "timevar.h"
#include "tree-dump.h"
#include "tree-flow.h"
if (TREE_CODE (dest) == SSA_NAME
&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest))
return false;
-
+
/* Do not copy between types for which we *do* need a conversion. */
if (!useless_type_conversion_p (type_d, type_o))
return false;
/* 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.
{
unsigned int dest_ver = SSA_NAME_VERSION (dest);
tree old_first, old_last, new_last;
-
+
/* Set FIRST to be the first link in COPY_OF[DEST]. If that
changed, return true. */
old_first = copy_of[dest_ver].value;
if (TREE_CODE (var) != SSA_NAME)
return;
-
+
visited = sbitmap_alloc (num_ssa_names);
sbitmap_zero (visited);
SET_BIT (visited, SSA_NAME_VERSION (var));
-
+
fprintf (file, " copy-of chain: ");
val = var;
fprintf (file, "[COPY]");
else
fprintf (file, "[NOT A COPY]");
-
+
sbitmap_free (visited);
}
lhs = gimple_assign_lhs (stmt);
rhs = gimple_assign_rhs1 (stmt);
-
+
gcc_assert (gimple_assign_rhs_code (stmt) == SSA_NAME);
copy of RHS's value, not of RHS itself. This avoids keeping
unnecessary copy-of chains (assignments cannot be in a cycle
like PHI nodes), speeding up the propagation process.
- This is different from what we do in copy_prop_visit_phi_node.
+ This is different from what we do in copy_prop_visit_phi_node.
In those cases, we are interested in the copy-of chains. */
*result_p = lhs;
if (set_copy_of_val (*result_p, rhs_val->value))
{
gimple_stmt_iterator si;
int depth = bb->loop_depth;
+ bool loop_exit_p = false;
for (si = gsi_start_bb (bb); !gsi_end_p (si); gsi_next (&si))
{
cached_last_copy_of[SSA_NAME_VERSION (def)] = def;
}
+ /* In loop-closed SSA form do not copy-propagate through
+ PHI nodes in blocks with a loop exit edge predecessor. */
+ if (current_loops
+ && loops_state_satisfies_p (LOOP_CLOSED_SSA))
+ {
+ edge_iterator ei;
+ edge e;
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ if (loop_exit_edge_p (e->src->loop_father, e))
+ loop_exit_p = true;
+ }
+
for (si = gsi_start_phis (bb); !gsi_end_p (si); gsi_next (&si))
{
gimple phi = gsi_stmt (si);
def = gimple_phi_result (phi);
if (!is_gimple_reg (def)
- /* In loop-closed SSA form do not copy-propagate through
- PHI nodes. Technically this is only needed for loop
- exit PHIs, but this is difficult to query. */
- || (current_loops
- && gimple_phi_num_args (phi) == 1
- && loops_state_satisfies_p (LOOP_CLOSED_SSA)))
+ || loop_exit_p)
prop_set_simulate_again (phi, false);
else
prop_set_simulate_again (phi, true);
{
size_t i;
prop_value_t *tmp;
-
+
/* Set the final copy-of value for each variable by traversing the
copy-of chains. */
tmp = XCNEWVEC (prop_value_t, num_ssa_names);
/* Main entry point to the copy propagator.
PHIS_ONLY is true if we should only consider PHI nodes as generating
- copy propagation opportunities.
+ copy propagation opportunities.
The algorithm propagates the value COPY-OF using ssa_propagate. For
every variable X_i, COPY-OF(X_i) indicates which variable is X_i created
Visit #2: a_2 is copy-of x_298. Value changed.
Visit #3: a_5 is copy-of x_298. Value changed.
Visit #4: x_1 is copy-of x_298. Stable state reached.
-
+
When visiting PHI nodes, we only consider arguments that flow
through edges marked executable by the propagation engine. So,
when visiting statement #2 for the first time, we will only look at
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
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):
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