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31f18eeb2b
Make it possible to prune individual graph edges from a post-order traversal by specializing the po_iterator_storage template. Previously, it was only possible to prune full graph nodes. Edge pruning makes it possible to remove loop back-edges, for example. Also replace the existing DFSetTraits customization hook with a po_iterator_storage method for observing the post-order. DFSetTraits was only used by LoopIterator.h which now provides a po_iterator_storage specialization. Thanks to Sean and Chandler for reviewing. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160366 91177308-0d34-0410-b5e6-96231b3b80d8
183 lines
6.1 KiB
C++
183 lines
6.1 KiB
C++
//===--------- LoopIterator.h - Iterate over loop blocks --------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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// This file defines iterators to visit the basic blocks within a loop.
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//
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// These iterators currently visit blocks within subloops as well.
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// Unfortunately we have no efficient way of summarizing loop exits which would
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// allow skipping subloops during traversal.
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//
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// If you want to visit all blocks in a loop and don't need an ordered traveral,
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// use Loop::block_begin() instead.
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//
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// This is intentionally designed to work with ill-formed loops in which the
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// backedge has been deleted. The only prerequisite is that all blocks
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// contained within the loop according to the most recent LoopInfo analysis are
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// reachable from the loop header.
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_LOOP_ITERATOR_H
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#define LLVM_ANALYSIS_LOOP_ITERATOR_H
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/PostOrderIterator.h"
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#include "llvm/Analysis/LoopInfo.h"
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namespace llvm {
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class LoopBlocksTraversal;
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/// Store the result of a depth first search within basic blocks contained by a
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/// single loop.
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///
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/// TODO: This could be generalized for any CFG region, or the entire CFG.
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class LoopBlocksDFS {
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public:
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/// Postorder list iterators.
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typedef std::vector<BasicBlock*>::const_iterator POIterator;
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typedef std::vector<BasicBlock*>::const_reverse_iterator RPOIterator;
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friend class LoopBlocksTraversal;
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private:
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Loop *L;
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/// Map each block to its postorder number. A block is only mapped after it is
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/// preorder visited by DFS. It's postorder number is initially zero and set
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/// to nonzero after it is finished by postorder traversal.
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DenseMap<BasicBlock*, unsigned> PostNumbers;
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std::vector<BasicBlock*> PostBlocks;
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public:
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LoopBlocksDFS(Loop *Container) :
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L(Container), PostNumbers(NextPowerOf2(Container->getNumBlocks())) {
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PostBlocks.reserve(Container->getNumBlocks());
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}
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Loop *getLoop() const { return L; }
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/// Traverse the loop blocks and store the DFS result.
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void perform(LoopInfo *LI);
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/// Return true if postorder numbers are assigned to all loop blocks.
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bool isComplete() const { return PostBlocks.size() == L->getNumBlocks(); }
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/// Iterate over the cached postorder blocks.
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POIterator beginPostorder() const {
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assert(isComplete() && "bad loop DFS");
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return PostBlocks.begin();
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}
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POIterator endPostorder() const { return PostBlocks.end(); }
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/// Reverse iterate over the cached postorder blocks.
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RPOIterator beginRPO() const {
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assert(isComplete() && "bad loop DFS");
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return PostBlocks.rbegin();
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}
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RPOIterator endRPO() const { return PostBlocks.rend(); }
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/// Return true if this block has been preorder visited.
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bool hasPreorder(BasicBlock *BB) const { return PostNumbers.count(BB); }
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/// Return true if this block has a postorder number.
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bool hasPostorder(BasicBlock *BB) const {
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DenseMap<BasicBlock*, unsigned>::const_iterator I = PostNumbers.find(BB);
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return I != PostNumbers.end() && I->second;
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}
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/// Get a block's postorder number.
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unsigned getPostorder(BasicBlock *BB) const {
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DenseMap<BasicBlock*, unsigned>::const_iterator I = PostNumbers.find(BB);
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assert(I != PostNumbers.end() && "block not visited by DFS");
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assert(I->second && "block not finished by DFS");
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return I->second;
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}
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/// Get a block's reverse postorder number.
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unsigned getRPO(BasicBlock *BB) const {
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return 1 + PostBlocks.size() - getPostorder(BB);
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}
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void clear() {
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PostNumbers.clear();
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PostBlocks.clear();
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}
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};
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/// Specialize po_iterator_storage to record postorder numbers.
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template<> class po_iterator_storage<LoopBlocksTraversal, true> {
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LoopBlocksTraversal &LBT;
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public:
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po_iterator_storage(LoopBlocksTraversal &lbs) : LBT(lbs) {}
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// These functions are defined below.
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bool insertEdge(BasicBlock *From, BasicBlock *To);
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void finishPostorder(BasicBlock *BB);
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};
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/// Traverse the blocks in a loop using a depth-first search.
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class LoopBlocksTraversal {
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public:
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/// Graph traversal iterator.
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typedef po_iterator<BasicBlock*, LoopBlocksTraversal, true> POTIterator;
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private:
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LoopBlocksDFS &DFS;
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LoopInfo *LI;
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public:
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LoopBlocksTraversal(LoopBlocksDFS &Storage, LoopInfo *LInfo) :
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DFS(Storage), LI(LInfo) {}
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/// Postorder traversal over the graph. This only needs to be done once.
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/// po_iterator "automatically" calls back to visitPreorder and
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/// finishPostorder to record the DFS result.
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POTIterator begin() {
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assert(DFS.PostBlocks.empty() && "Need clear DFS result before traversing");
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assert(DFS.L->getNumBlocks() && "po_iterator cannot handle an empty graph");
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return po_ext_begin(DFS.L->getHeader(), *this);
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}
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POTIterator end() {
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// po_ext_end interface requires a basic block, but ignores its value.
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return po_ext_end(DFS.L->getHeader(), *this);
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}
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/// Called by po_iterator upon reaching a block via a CFG edge. If this block
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/// is contained in the loop and has not been visited, then mark it preorder
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/// visited and return true.
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///
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/// TODO: If anyone is interested, we could record preorder numbers here.
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bool visitPreorder(BasicBlock *BB) {
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if (!DFS.L->contains(LI->getLoopFor(BB)))
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return false;
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return DFS.PostNumbers.insert(std::make_pair(BB, 0)).second;
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}
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/// Called by po_iterator each time it advances, indicating a block's
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/// postorder.
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void finishPostorder(BasicBlock *BB) {
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assert(DFS.PostNumbers.count(BB) && "Loop DFS skipped preorder");
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DFS.PostBlocks.push_back(BB);
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DFS.PostNumbers[BB] = DFS.PostBlocks.size();
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}
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};
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inline bool po_iterator_storage<LoopBlocksTraversal, true>::
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insertEdge(BasicBlock *From, BasicBlock *To) {
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return LBT.visitPreorder(To);
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}
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inline void po_iterator_storage<LoopBlocksTraversal, true>::
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finishPostorder(BasicBlock *BB) {
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LBT.finishPostorder(BB);
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}
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} // End namespace llvm
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#endif
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