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VedantParanjapeVedantParanjape
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Add support for basic blocks and CFGs
Added class for representing basic blocks, and a helper function to generate basic blocks from AST. For testing, disabled the loop_finder code.
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4 files changed

+211
-14
lines changed

4 files changed

+211
-14
lines changed

‎include/blocks/basic_blocks.h‎

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#ifndef BASIC_BLOCKS_H
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#define BASIC_BLOCKS_H
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#include "blocks/block_visitor.h"
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#include "blocks/stmt.h"
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#include <vector>
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#include <deque>
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#include <string>
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class basic_block {
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public:
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basic_block(std::string label): name(label) {};
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std::vector<std::shared_ptr<basic_block>> predecessor;
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std::vector<std::shared_ptr<basic_block>> successor;
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block::expr::Ptr branch_expr;
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block::stmt::Ptr parent;
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std::string name;
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};
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std::vector<std::shared_ptr<basic_block>> generate_basic_blocks(block::stmt_block::Ptr ast);
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#endif

‎include/blocks/loop_finder.h‎

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@@ -2,6 +2,7 @@
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#define LOOP_FINDER_H
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#include "blocks/block_visitor.h"
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#include "blocks/stmt.h"
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#include "blocks/basic_blocks.h"
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namespace block {
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class loop_finder : public block_visitor {

‎src/blocks/basic_blocks.cpp‎

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#include "blocks/basic_blocks.h"
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#include <algorithm>
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using namespace block;
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std::vector<std::shared_ptr<basic_block>> generate_basic_blocks(block::stmt_block::Ptr ast) {
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std::deque<std::shared_ptr<basic_block>> work_list;
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std::vector<std::shared_ptr<basic_block>> return_list;
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int basic_block_count = 0;
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// step 1: fill the work_list
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for (auto st: ast->stmts) {
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auto bb = std::make_shared<basic_block>(std::to_string(basic_block_count));
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bb->parent = st;
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work_list.push_back(bb);
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basic_block_count++;
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}
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// step 2: add successors
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for (unsigned i = 0; work_list.size() != 0 && i < work_list.size() - 1; i++) {
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work_list[i]->successor.push_back(work_list[i+1]);
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}
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// step 3: process blocks
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while (work_list.size()) {
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auto bb = work_list.front();
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if (isa<block::stmt_block>(bb->parent)) {
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stmt_block::Ptr stmt_block_ = to<stmt_block>(bb->parent);
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bb->name = "stmt" + bb->name;
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if (stmt_block_->stmts.size() > 0) {
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std::vector<std::shared_ptr<basic_block>> stmt_block_list;
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for (auto st: stmt_block_->stmts) {
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stmt_block_list.push_back(std::make_shared<basic_block>(std::to_string(basic_block_count++)));
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stmt_block_list.back()->parent = st;
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}
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for (unsigned i = 0; stmt_block_list.size() != 0 && i < stmt_block_list.size() - 1; i++) {
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stmt_block_list[i]->successor.push_back(stmt_block_list[i+1]);
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}
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stmt_block_list.back()->successor.push_back(bb->successor.front());
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bb->successor.clear();
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bb->successor.push_back(stmt_block_list.front());
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return_list.push_back(bb);
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work_list.pop_front();
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work_list.insert(work_list.begin(), stmt_block_list.begin(), stmt_block_list.end());
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}
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else {
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return_list.push_back(bb);
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work_list.pop_front();
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}
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}
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else if (isa<if_stmt>(bb->parent)) {
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bb->name = "if" + bb->name;
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if_stmt::Ptr if_stmt_ = to<if_stmt>(bb->parent);
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// assign the if condition to the basic block
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bb->branch_expr = if_stmt_->cond;
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// create a exit block
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auto exit_bb = std::make_shared<basic_block>("exit" + std::to_string(basic_block_count));
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// assign it a empty stmt_block as parent
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exit_bb->parent = std::make_shared<stmt_block>();
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// check if this is the last block, if yes the successor will be empty
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if (bb->successor.size()) {
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// set the successor to the block that if_stmt pointer to earlier
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exit_bb->successor.push_back(bb->successor.front());
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// clear the successor block from the if_stmt
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bb->successor.clear();
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}
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// remove the if from the work_list
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work_list.pop_front();
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// push the exit block to the work_list
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work_list.push_front(exit_bb);
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// if there is a then_stmt, create a basic block for it
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if (to<stmt_block>(if_stmt_->then_stmt)->stmts.size() != 0) {
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auto then_bb = std::make_shared<basic_block>(std::to_string(++basic_block_count));
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// set the parent of this block as the then stmts
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then_bb->parent = if_stmt_->then_stmt;
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// set the successor of this block to be the exit block
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then_bb->successor.push_back(exit_bb);
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// set the successor of the original if_stmt block to be this then block
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bb->successor.push_back(then_bb);
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// push the block to the work_list, to expand it further
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work_list.push_front(then_bb);
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}
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// if there is a else_stmt, create a basic block for it
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if (to<stmt_block>(if_stmt_->else_stmt)->stmts.size() != 0) {
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auto else_bb = std::make_shared<basic_block>(std::to_string(++basic_block_count));
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// set the parent of this block as the else stmts
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else_bb->parent = if_stmt_->else_stmt;
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// set the successor of this block to be the exit block
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else_bb->successor.push_back(exit_bb);
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// set the successor of the orignal if_stmt block to be this else block
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bb->successor.push_back(else_bb);
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// push the block to the work_list, to expand it further
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work_list.insert(work_list.begin() + 1, else_bb);
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}
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// if there is no else block, then have the exit block as successor as well.
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if (bb->successor.size() <= 1) bb->successor.push_back(exit_bb);
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return_list.push_back(bb);
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}
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else if (isa<block::expr_stmt>(bb->parent)) {
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bb->name = "expr" + bb->name;
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return_list.push_back(bb);
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work_list.pop_front();
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}
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else if (isa<block::decl_stmt>(bb->parent)) {
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bb->name = "decl" + bb->name;
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return_list.push_back(bb);
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work_list.pop_front();
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}
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else if (isa<block::label_stmt>(bb->parent)) {
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bb->name = "label" + bb->name;
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return_list.push_back(bb);
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work_list.pop_front();
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}
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else if (isa<block::goto_stmt>(bb->parent)) {
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bb->name = "goto" + bb->name;
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return_list.push_back(bb);
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work_list.pop_front();
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}
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else if (isa<block::return_stmt>(bb->parent)) {
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bb->name = "return" + bb->name;
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return_list.push_back(bb);
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work_list.pop_front();
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}
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basic_block_count++;
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}
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// step 4: resolve goto calls to successors of labels
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for (auto bb: return_list) {
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if (isa<block::goto_stmt>(bb->parent)) {
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auto goto_source = std::find_if(return_list.begin(), return_list.end(),
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[bb](std::shared_ptr<basic_block> bb_l) {
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if (isa<label_stmt>(bb_l->parent)) {
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return to<label_stmt>(bb_l->parent)->label1 == to<goto_stmt>(bb->parent)->label1;
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}
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return false;
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});
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if (goto_source != return_list.end()) {
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bb->successor.clear();
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bb->successor.push_back(*goto_source);
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}
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}
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}
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return return_list;
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}

‎src/blocks/loop_finder.cpp‎

Lines changed: 31 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -129,22 +129,39 @@ static void trim_from_parents(std::vector<stmt_block::Ptr> &parents, std::vector
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}
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void loop_finder::visit(stmt_block::Ptr a) {
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// Check if this block has a label
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while (1) {
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label_stmt::Ptr found_label = nullptr;
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for (auto stmt : a->stmts) {
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if (isa<label_stmt>(stmt)) {
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found_label = to<label_stmt>(stmt);
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}
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std::vector<std::shared_ptr<basic_block>> BBs = generate_basic_blocks(a);
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std::cout << "++++++ basic blocks ++++++ \n";
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for (auto bb: BBs) {
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std::cout << bb->name << ":" << "\n";
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if (bb->branch_expr) {
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std::cout << " ";
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bb->branch_expr->dump(std::cout, 0);
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}
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if (found_label == nullptr)
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break;
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visit_label(found_label, a);
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}
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// Once all labels are done, visit the instructions normally
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for (auto stmt : a->stmts) {
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stmt->accept(this);
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std::cout << " ";
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std::cout << "br ";
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for (auto branches: bb->successor) {
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std::cout << branches->name << ", ";
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}
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std::cout << "\n";
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}
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std::cout << "++++++ basic blocks ++++++ \n";
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// while (1) {
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// label_stmt::Ptr found_label = nullptr;
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// for (auto stmt : a->stmts) {
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// if (isa<label_stmt>(stmt)) {
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// found_label = to<label_stmt>(stmt);
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// }
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// }
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// if (found_label == nullptr)
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// break;
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// visit_label(found_label, a);
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// }
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// // Once all labels are done, visit the instructions normally
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// for (auto stmt : a->stmts) {
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// stmt->accept(this);
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// }
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}
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void loop_finder::visit_label(label_stmt::Ptr a, stmt_block::Ptr parent) {
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