Viewing file:  Remove_loop_booleans.cpp (4 KB) -rw-rw-r--
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/*
* phc -- the open source PHP compiler
* See doc/license/README.license for licensing information
*
* For-loops are converted to an unusual form:
*
* loop_init ();
* $first = true;
* L0:
* if ($first) goto L1; else goto L2;
* L1:
* $first = false;
* goto L3;
* L2:
* loop_incr ();
* goto L3;
* L3:
* $cond = loop_cond ();
* if (!$cond) goto L4; else goto L5;
* L4:
* loop_body ();
* goto L0;
* L5:
*
* We wish to remove the messing around with the booleans by splitting the
* 'if ($first) block in two, and letting the optimizers at it (which will
* remove them).
*
* We convert this to:
*
* loop_init ();
* $first = true;
* goto L0a:
* L0a:
* if ($first) goto L1; else goto L2;
* L0b:
* if ($first) goto L1; else goto L2;
* L1:
* $first = false;
* goto L3;
* L2:
* loop_incr ();
* goto L3;
* L3:
* $cond = loop_cond ();
* if (!$cond) goto L4; else goto L5;
* L4:
* loop_body ();
* goto L0b;
* L5:
*
* Then the SCCP and DCE should kill a lot of statements, leaving:
*
* loop_init ();
* goto L3;
* L2:
* loop_incr ();
* L3:
* $cond = loop_cond ();
* if (!$cond) goto L4; else goto L5;
* L4:
* loop_body ();
* goto L2;
*
* While it is correct to do this anywhere, we dont want to do it unless it
* will result in a win. Identifying a win is tricky, so we'll just look for
* identifying features.
*
* Its vastly simpler to do this out-of-SSA than in it.
* TODO: simpler to annotate it in the Early_lower_control_flow maybe?
* TODO: this should get both do_while loops and foreach
*/
#include "Remove_loop_booleans.h"
#include "process_ir/General.h"
#include "Def_use_web.h"
#include "wpa/Def_use.h"
#include "wpa/Points_to.h"
using namespace MIR;
void
Remove_loop_booleans::visit_branch_block (Branch_block* bb)
{
if (is_applicable_branch (bb))
bb->cfg->split_block (bb);
}
bool
Remove_loop_booleans::is_applicable_branch (Branch_block* bb)
{
// Identifying the circumstance is very specific:
// - The boolean is defined has two defs
// - The first def is to true, and is in the predecessor
// - the second def is to false, and is in a successor
if (bb->get_predecessors()->size() < 2)
return false;
Context* cx = Context::non_contextual (bb);
string ns = cx->symtable_name ();
// Extract the correct use from the branch
SSA_use* use;
bool proceed = false;
foreach (SSA_use* temp, *bb->cfg->duw->get_block_uses (bb))
{
if (temp->type_flag != SSA_PHI)
{
string s = temp->name->get_name ();
Index_node name (ns, *bb->branch->variable_name->value);
if (s == name.get_starred_name ()->str())
{
use = temp;
proceed = true;
}
}
}
if (!proceed)
{
// There should be a use of the branch variable in a branch block, right?
phc_unreachable ();
}
if (!bb->branch->variable_name->attrs->has ("phc.codegen.compiler_generated"))
return false;
SSA_def_list* defs = use->get_defs (); // Needs to not be in SSA...
// Check if there are two defs
if (defs->size () != 2)
return false;
Basic_block* bb0 = defs->front ()->bb;
Basic_block* bb1 = defs->back ()->bb;
Basic_block* true_bb;
Basic_block* false_bb;
if (bb0->get_successors ()->has (bb)
&& bb->get_successors ()->has (bb1))
{
true_bb = bb0;
false_bb = bb1;
}
else if (bb1->get_successors ()->has (bb)
&& bb->get_successors ()->has (bb0))
{
true_bb = bb1;
false_bb = bb0;
}
else
return false;
// Might need to do a dynamic_cast instead of dyc in the below two blocks, since if the branch variable is argv or argc,
// it'll be defined in the entry block, not a statement block (???)
// The predecessor is the true block
if (!(dyc<Statement_block> (true_bb))->statement->match (
new Assign_var (
bb->branch->variable_name,
false,
new BOOL (true))))
return false;
// Successor is the false block
if (!(dyc<Statement_block> (false_bb))->statement->match (
new Assign_var (
bb->branch->variable_name,
false,
new BOOL (false))))
return false;
return true;
}
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