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/*
* phc -- the open source PHP compiler
* See doc/license/README.license for licensing information
*
* Mark variables as definitely initialized, or definitely uninitialized, or
* maybe initialized.
*
* When we generate code, we wish to know if the variable was are
* using/defining is already initialized. This allows us avoid a number of
* checks.
*
* Though SSA form guarantees that a variable only has a single definition,
* we do not generate code in SSA form. Rather, we drop SSA indices and operate
* on the base names. So we need to propagate whether or not the _base_name_
* has been initialized, to each SSA name being defined.
*
* If we were to use SSA form, we would have a problem with definitions of
* different versions of the same variable. We do not have a link between x_0
* and x_1, so if we store a result in x_0, we have no way to know at x_1 that
* it is the correct data to use (nor can we easily search for it).
*
* We instead use a more traditional dataflow technique of simply propagating
* the list of initialized variables.
*
* Notes:
* - assignment to NULL and UNSET are different in this context - NULL
* leaves the variable initialized. unset makes the variable uninitialized
* (even for indirect assignments).
*
* - aliasing doesnt affect things - indirect assignments can only occur for
* initialized variables, and do not affect the results.
*
*
* TODO: this is another place that would benefit from splitting branches with
* multiple predecessors (though it might be turned off in the case of space
* constaints).
*
* TODO: it may be useful to initialize variables to ensure we know this in all
* cases.
*/
#ifndef PHC_MARK_INITIALIZED
#define PHC_MARK_INITIALIZED
#include "CFG.h"
#include "CFG_visitor.h"
#include "Edge.h"
#include "Def_use_web.h"
#include "Lattice.h"
#include "process_ir/debug.h"
class Init_cell : virtual public GC_obj
{
public:
void dump (std::ostream& os = cdebug);
bool equals (Init_cell*);
// We only need one instance of INIT and UNINIT, since they're all the same.
static Init_cell* INIT;
static Init_cell* UNINIT;
};
// TOP -> INIT -> BOTTOM
// UNINIT
/*
class Mark_initialized : public Flow_visitor
{
Map<Basic_block*, Var_set> local_defs;
Map<Basic_block*, Var_set> local_undefs;
Map<Basic_block*, SSA_map*> ins;
Map<Basic_block*, SSA_map*> outs;
Map<Basic_block*, bool> repeat;
Map<Basic_block*, bool> executed;
public:
Mark_initialized ();
void init_block (Basic_block*);
// Local solution
void visit_entry_block (Entry_block*);
void visit_statement_block (Statement_block*);
// Flow
void transfer_in (Basic_block* bb, BB_list*);
void transfer_out (Basic_block* bb, BB_list*);
bool solution_has_changed (Basic_block*);
// Use the analysis
void post_pass (CFG* cfg);
};
*/
#endif // PHC_MARK_INITIALIZED
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