SPIRV-Tools/source/opt/dominator_tree.h

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// Copyright (c) 2017 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef SOURCE_OPT_DOMINATOR_TREE_H_
#define SOURCE_OPT_DOMINATOR_TREE_H_
#include <algorithm>
#include <cstdint>
#include <map>
#include <utility>
#include <vector>
#include "source/opt/cfg.h"
#include "source/opt/tree_iterator.h"
namespace spvtools {
namespace opt {
// This helper struct forms the nodes in the tree, with each node containing its
// children. It also contains two values, for the pre and post indexes in the
// tree which are used to compare two nodes.
struct DominatorTreeNode {
explicit DominatorTreeNode(BasicBlock* bb)
: bb_(bb),
parent_(nullptr),
children_({}),
dfs_num_pre_(-1),
dfs_num_post_(-1) {}
using iterator = std::vector<DominatorTreeNode*>::iterator;
using const_iterator = std::vector<DominatorTreeNode*>::const_iterator;
// depth first preorder iterator.
using df_iterator = TreeDFIterator<DominatorTreeNode>;
using const_df_iterator = TreeDFIterator<const DominatorTreeNode>;
// depth first postorder iterator.
using post_iterator = PostOrderTreeDFIterator<DominatorTreeNode>;
using const_post_iterator = PostOrderTreeDFIterator<const DominatorTreeNode>;
iterator begin() { return children_.begin(); }
iterator end() { return children_.end(); }
const_iterator begin() const { return cbegin(); }
const_iterator end() const { return cend(); }
const_iterator cbegin() const { return children_.begin(); }
const_iterator cend() const { return children_.end(); }
// Depth first preorder iterator using this node as root.
df_iterator df_begin() { return df_iterator(this); }
df_iterator df_end() { return df_iterator(); }
const_df_iterator df_begin() const { return df_cbegin(); }
const_df_iterator df_end() const { return df_cend(); }
const_df_iterator df_cbegin() const { return const_df_iterator(this); }
const_df_iterator df_cend() const { return const_df_iterator(); }
// Depth first postorder iterator using this node as root.
post_iterator post_begin() { return post_iterator::begin(this); }
post_iterator post_end() { return post_iterator::end(nullptr); }
const_post_iterator post_begin() const { return post_cbegin(); }
const_post_iterator post_end() const { return post_cend(); }
const_post_iterator post_cbegin() const {
return const_post_iterator::begin(this);
}
const_post_iterator post_cend() const {
return const_post_iterator::end(nullptr);
}
inline uint32_t id() const { return bb_->id(); }
BasicBlock* bb_;
DominatorTreeNode* parent_;
std::vector<DominatorTreeNode*> children_;
// These indexes are used to compare two given nodes. A node is a child or
// grandchild of another node if its preorder index is greater than the
// first nodes preorder index AND if its postorder index is less than the
// first nodes postorder index.
int dfs_num_pre_;
int dfs_num_post_;
};
// A class representing a tree of BasicBlocks in a given function, where each
// node is dominated by its parent.
class DominatorTree {
public:
// Map OpLabel ids to dominator tree nodes
using DominatorTreeNodeMap = std::map<uint32_t, DominatorTreeNode>;
using iterator = TreeDFIterator<DominatorTreeNode>;
using const_iterator = TreeDFIterator<const DominatorTreeNode>;
using post_iterator = PostOrderTreeDFIterator<DominatorTreeNode>;
using const_post_iterator = PostOrderTreeDFIterator<const DominatorTreeNode>;
// List of DominatorTreeNode to define the list of roots
using DominatorTreeNodeList = std::vector<DominatorTreeNode*>;
using roots_iterator = DominatorTreeNodeList::iterator;
using roots_const_iterator = DominatorTreeNodeList::const_iterator;
DominatorTree() : postdominator_(false) {}
explicit DominatorTree(bool post) : postdominator_(post) {}
// Depth first iterators.
// Traverse the dominator tree in a depth first pre-order.
// The pseudo-block is ignored.
iterator begin() { return ++iterator(GetRoot()); }
iterator end() { return iterator(); }
const_iterator begin() const { return cbegin(); }
const_iterator end() const { return cend(); }
const_iterator cbegin() const { return ++const_iterator(GetRoot()); }
const_iterator cend() const { return const_iterator(); }
// Traverse the dominator tree in a depth first post-order.
// The pseudo-block is ignored.
post_iterator post_begin() { return post_iterator::begin(GetRoot()); }
post_iterator post_end() { return post_iterator::end(GetRoot()); }
const_post_iterator post_begin() const { return post_cbegin(); }
const_post_iterator post_end() const { return post_cend(); }
const_post_iterator post_cbegin() const {
return const_post_iterator::begin(GetRoot());
}
const_post_iterator post_cend() const {
return const_post_iterator::end(GetRoot());
}
roots_iterator roots_begin() { return roots_.begin(); }
roots_iterator roots_end() { return roots_.end(); }
roots_const_iterator roots_begin() const { return roots_cbegin(); }
roots_const_iterator roots_end() const { return roots_cend(); }
roots_const_iterator roots_cbegin() const { return roots_.begin(); }
roots_const_iterator roots_cend() const { return roots_.end(); }
// Get the unique root of the tree.
// It is guaranteed to work on a dominator tree.
// post-dominator might have a list.
DominatorTreeNode* GetRoot() {
assert(roots_.size() == 1);
return *roots_.begin();
}
const DominatorTreeNode* GetRoot() const {
assert(roots_.size() == 1);
return *roots_.begin();
}
const DominatorTreeNodeList& Roots() const { return roots_; }
// Dumps the tree in the graphvis dot format into the |out_stream|.
void DumpTreeAsDot(std::ostream& out_stream) const;
// Build the (post-)dominator tree for the given control flow graph
// |cfg| and the function |f|. |f| must exist in the |cfg|. Any
// existing data in the dominator tree will be overwritten
void InitializeTree(const CFG& cfg, const Function* f);
// Check if the basic block |a| dominates the basic block |b|.
bool Dominates(const BasicBlock* a, const BasicBlock* b) const;
// Check if the basic block id |a| dominates the basic block id |b|.
bool Dominates(uint32_t a, uint32_t b) const;
// Check if the dominator tree node |a| dominates the dominator tree node |b|.
bool Dominates(const DominatorTreeNode* a, const DominatorTreeNode* b) const;
// Check if the basic block |a| strictly dominates the basic block |b|.
bool StrictlyDominates(const BasicBlock* a, const BasicBlock* b) const;
// Check if the basic block id |a| strictly dominates the basic block id |b|.
bool StrictlyDominates(uint32_t a, uint32_t b) const;
// Check if the dominator tree node |a| strictly dominates the dominator tree
// node |b|.
bool StrictlyDominates(const DominatorTreeNode* a,
const DominatorTreeNode* b) const;
// Returns the immediate dominator of basic block |a|.
BasicBlock* ImmediateDominator(const BasicBlock* A) const;
// Returns the immediate dominator of basic block id |a|.
BasicBlock* ImmediateDominator(uint32_t a) const;
// Returns true if the basic block |a| is reachable by this tree. A node would
// be unreachable if it cannot be reached by traversal from the start node or
// for a postdominator tree, cannot be reached from the exit nodes.
inline bool ReachableFromRoots(const BasicBlock* a) const {
if (!a) return false;
return ReachableFromRoots(a->id());
}
// Returns true if the basic block id |a| is reachable by this tree.
bool ReachableFromRoots(uint32_t a) const {
return GetTreeNode(a) != nullptr;
}
// Returns true if this tree is a post dominator tree.
bool IsPostDominator() const { return postdominator_; }
// Clean up the tree.
void ClearTree() {
nodes_.clear();
roots_.clear();
}
// Applies the std::function |func| to all nodes in the dominator tree.
// Tree nodes are visited in a depth first pre-order.
bool Visit(std::function<bool(DominatorTreeNode*)> func) {
for (auto n : *this) {
if (!func(&n)) return false;
}
return true;
}
// Applies the std::function |func| to all nodes in the dominator tree.
// Tree nodes are visited in a depth first pre-order.
bool Visit(std::function<bool(const DominatorTreeNode*)> func) const {
for (auto n : *this) {
if (!func(&n)) return false;
}
return true;
}
// Applies the std::function |func| to all nodes in the dominator tree from
// |node| downwards. The boolean return from |func| is used to determine
// whether or not the children should also be traversed. Tree nodes are
// visited in a depth first pre-order.
void VisitChildrenIf(std::function<bool(DominatorTreeNode*)> func,
iterator node) {
if (func(&*node)) {
for (auto n : *node) {
VisitChildrenIf(func, n->df_begin());
}
}
}
// Returns the DominatorTreeNode associated with the basic block |bb|.
// If the |bb| is unknown to the dominator tree, it returns null.
inline DominatorTreeNode* GetTreeNode(BasicBlock* bb) {
return GetTreeNode(bb->id());
}
// Returns the DominatorTreeNode associated with the basic block |bb|.
// If the |bb| is unknown to the dominator tree, it returns null.
inline const DominatorTreeNode* GetTreeNode(BasicBlock* bb) const {
return GetTreeNode(bb->id());
}
// Returns the DominatorTreeNode associated with the basic block id |id|.
// If the id |id| is unknown to the dominator tree, it returns null.
inline DominatorTreeNode* GetTreeNode(uint32_t id) {
DominatorTreeNodeMap::iterator node_iter = nodes_.find(id);
if (node_iter == nodes_.end()) {
return nullptr;
}
return &node_iter->second;
}
// Returns the DominatorTreeNode associated with the basic block id |id|.
// If the id |id| is unknown to the dominator tree, it returns null.
inline const DominatorTreeNode* GetTreeNode(uint32_t id) const {
DominatorTreeNodeMap::const_iterator node_iter = nodes_.find(id);
if (node_iter == nodes_.end()) {
return nullptr;
}
return &node_iter->second;
}
// Adds the basic block |bb| to the tree structure if it doesn't already
// exist.
DominatorTreeNode* GetOrInsertNode(BasicBlock* bb);
// Recomputes the DF numbering of the tree.
void ResetDFNumbering();
private:
// Wrapper function which gets the list of pairs of each BasicBlocks to its
// immediately dominating BasicBlock and stores the result in the the edges
// parameter.
//
// The |edges| vector will contain the dominator tree as pairs of nodes.
// The first node in the pair is a node in the graph. The second node in the
// pair is its immediate dominator.
// The root of the tree has themself as immediate dominator.
void GetDominatorEdges(
const Function* f, const BasicBlock* dummy_start_node,
std::vector<std::pair<BasicBlock*, BasicBlock*>>* edges);
// The roots of the tree.
std::vector<DominatorTreeNode*> roots_;
// Pairs each basic block id to the tree node containing that basic block.
DominatorTreeNodeMap nodes_;
// True if this is a post dominator tree.
bool postdominator_;
};
} // namespace opt
} // namespace spvtools
#endif // SOURCE_OPT_DOMINATOR_TREE_H_