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unswitch when frontier includes basic blocks that are not inside loop. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42654 91177308-0d34-0410-b5e6-96231b3b80d8
592 lines
20 KiB
C++
592 lines
20 KiB
C++
//===- Dominators.cpp - Dominator Calculation -----------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements simple dominator construction algorithms for finding
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// forward dominators. Postdominators are available in libanalysis, but are not
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// included in libvmcore, because it's not needed. Forward dominators are
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// needed to support the Verifier pass.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Assembly/Writer.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/SetOperations.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Analysis/DominatorInternals.h"
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#include "llvm/Instructions.h"
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#include "llvm/Support/Streams.h"
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#include <algorithm>
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using namespace llvm;
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namespace llvm {
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static std::ostream &operator<<(std::ostream &o,
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const std::set<BasicBlock*> &BBs) {
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for (std::set<BasicBlock*>::const_iterator I = BBs.begin(), E = BBs.end();
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I != E; ++I)
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if (*I)
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WriteAsOperand(o, *I, false);
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else
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o << " <<exit node>>";
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return o;
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}
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}
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//===----------------------------------------------------------------------===//
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// DominatorTree Implementation
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//===----------------------------------------------------------------------===//
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//
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// Provide public access to DominatorTree information. Implementation details
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// can be found in DominatorCalculation.h.
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//
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//===----------------------------------------------------------------------===//
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char DominatorTree::ID = 0;
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static RegisterPass<DominatorTree>
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E("domtree", "Dominator Tree Construction", true);
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// NewBB is split and now it has one successor. Update dominator tree to
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// reflect this change.
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void DominatorTree::splitBlock(BasicBlock *NewBB) {
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assert(NewBB->getTerminator()->getNumSuccessors() == 1
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&& "NewBB should have a single successor!");
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BasicBlock *NewBBSucc = NewBB->getTerminator()->getSuccessor(0);
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std::vector<BasicBlock*> PredBlocks;
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for (pred_iterator PI = pred_begin(NewBB), PE = pred_end(NewBB);
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PI != PE; ++PI)
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PredBlocks.push_back(*PI);
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assert(!PredBlocks.empty() && "No predblocks??");
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// The newly inserted basic block will dominate existing basic blocks iff the
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// PredBlocks dominate all of the non-pred blocks. If all predblocks dominate
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// the non-pred blocks, then they all must be the same block!
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//
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bool NewBBDominatesNewBBSucc = true;
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{
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BasicBlock *OnePred = PredBlocks[0];
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unsigned i = 1, e = PredBlocks.size();
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for (i = 1; !isReachableFromEntry(OnePred); ++i) {
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assert(i != e && "Didn't find reachable pred?");
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OnePred = PredBlocks[i];
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}
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for (; i != e; ++i)
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if (PredBlocks[i] != OnePred && isReachableFromEntry(OnePred)) {
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NewBBDominatesNewBBSucc = false;
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break;
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}
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if (NewBBDominatesNewBBSucc)
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for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
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PI != E; ++PI)
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if (*PI != NewBB && !dominates(NewBBSucc, *PI)) {
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NewBBDominatesNewBBSucc = false;
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break;
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}
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}
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// The other scenario where the new block can dominate its successors are when
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// all predecessors of NewBBSucc that are not NewBB are dominated by NewBBSucc
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// already.
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if (!NewBBDominatesNewBBSucc) {
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NewBBDominatesNewBBSucc = true;
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for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
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PI != E; ++PI)
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if (*PI != NewBB && !dominates(NewBBSucc, *PI)) {
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NewBBDominatesNewBBSucc = false;
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break;
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}
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}
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// Find NewBB's immediate dominator and create new dominator tree node for
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// NewBB.
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BasicBlock *NewBBIDom = 0;
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unsigned i = 0;
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for (i = 0; i < PredBlocks.size(); ++i)
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if (isReachableFromEntry(PredBlocks[i])) {
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NewBBIDom = PredBlocks[i];
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break;
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}
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assert(i != PredBlocks.size() && "No reachable preds?");
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for (i = i + 1; i < PredBlocks.size(); ++i) {
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if (isReachableFromEntry(PredBlocks[i]))
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NewBBIDom = findNearestCommonDominator(NewBBIDom, PredBlocks[i]);
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}
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assert(NewBBIDom && "No immediate dominator found??");
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// Create the new dominator tree node... and set the idom of NewBB.
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DomTreeNode *NewBBNode = addNewBlock(NewBB, NewBBIDom);
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// If NewBB strictly dominates other blocks, then it is now the immediate
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// dominator of NewBBSucc. Update the dominator tree as appropriate.
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if (NewBBDominatesNewBBSucc) {
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DomTreeNode *NewBBSuccNode = getNode(NewBBSucc);
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changeImmediateDominator(NewBBSuccNode, NewBBNode);
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}
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}
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void DominatorTreeBase::updateDFSNumbers() {
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unsigned DFSNum = 0;
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SmallVector<std::pair<DomTreeNode*, DomTreeNode::iterator>, 32> WorkStack;
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for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
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DomTreeNode *ThisRoot = getNode(Roots[i]);
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WorkStack.push_back(std::make_pair(ThisRoot, ThisRoot->begin()));
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ThisRoot->DFSNumIn = DFSNum++;
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while (!WorkStack.empty()) {
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DomTreeNode *Node = WorkStack.back().first;
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DomTreeNode::iterator ChildIt = WorkStack.back().second;
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// If we visited all of the children of this node, "recurse" back up the
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// stack setting the DFOutNum.
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if (ChildIt == Node->end()) {
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Node->DFSNumOut = DFSNum++;
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WorkStack.pop_back();
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} else {
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// Otherwise, recursively visit this child.
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DomTreeNode *Child = *ChildIt;
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++WorkStack.back().second;
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WorkStack.push_back(std::make_pair(Child, Child->begin()));
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Child->DFSNumIn = DFSNum++;
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}
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}
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}
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SlowQueries = 0;
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DFSInfoValid = true;
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}
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/// isReachableFromEntry - Return true if A is dominated by the entry
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/// block of the function containing it.
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const bool DominatorTreeBase::isReachableFromEntry(BasicBlock* A) {
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assert (!isPostDominator()
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&& "This is not implemented for post dominators");
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return dominates(&A->getParent()->getEntryBlock(), A);
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}
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// dominates - Return true if A dominates B. THis performs the
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// special checks necessary if A and B are in the same basic block.
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bool DominatorTreeBase::dominates(Instruction *A, Instruction *B) {
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BasicBlock *BBA = A->getParent(), *BBB = B->getParent();
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if (BBA != BBB) return dominates(BBA, BBB);
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// It is not possible to determine dominance between two PHI nodes
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// based on their ordering.
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if (isa<PHINode>(A) && isa<PHINode>(B))
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return false;
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// Loop through the basic block until we find A or B.
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BasicBlock::iterator I = BBA->begin();
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for (; &*I != A && &*I != B; ++I) /*empty*/;
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if(!IsPostDominators) {
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// A dominates B if it is found first in the basic block.
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return &*I == A;
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} else {
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// A post-dominates B if B is found first in the basic block.
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return &*I == B;
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}
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}
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// DominatorTreeBase::reset - Free all of the tree node memory.
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//
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void DominatorTreeBase::reset() {
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for (DomTreeNodeMapType::iterator I = DomTreeNodes.begin(),
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E = DomTreeNodes.end(); I != E; ++I)
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delete I->second;
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DomTreeNodes.clear();
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IDoms.clear();
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Roots.clear();
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Vertex.clear();
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RootNode = 0;
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}
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DomTreeNode *DominatorTreeBase::getNodeForBlock(BasicBlock *BB) {
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if (DomTreeNode *BBNode = DomTreeNodes[BB])
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return BBNode;
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// Haven't calculated this node yet? Get or calculate the node for the
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// immediate dominator.
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BasicBlock *IDom = getIDom(BB);
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DomTreeNode *IDomNode = getNodeForBlock(IDom);
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// Add a new tree node for this BasicBlock, and link it as a child of
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// IDomNode
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DomTreeNode *C = new DomTreeNode(BB, IDomNode);
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return DomTreeNodes[BB] = IDomNode->addChild(C);
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}
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/// findNearestCommonDominator - Find nearest common dominator basic block
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/// for basic block A and B. If there is no such block then return NULL.
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BasicBlock *DominatorTreeBase::findNearestCommonDominator(BasicBlock *A,
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BasicBlock *B) {
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assert (!isPostDominator()
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&& "This is not implemented for post dominators");
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assert (A->getParent() == B->getParent()
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&& "Two blocks are not in same function");
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// If either A or B is a entry block then it is nearest common dominator.
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BasicBlock &Entry = A->getParent()->getEntryBlock();
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if (A == &Entry || B == &Entry)
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return &Entry;
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// If B dominates A then B is nearest common dominator.
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if (dominates(B, A))
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return B;
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// If A dominates B then A is nearest common dominator.
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if (dominates(A, B))
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return A;
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DomTreeNode *NodeA = getNode(A);
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DomTreeNode *NodeB = getNode(B);
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// Collect NodeA dominators set.
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SmallPtrSet<DomTreeNode*, 16> NodeADoms;
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NodeADoms.insert(NodeA);
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DomTreeNode *IDomA = NodeA->getIDom();
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while (IDomA) {
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NodeADoms.insert(IDomA);
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IDomA = IDomA->getIDom();
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}
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// Walk NodeB immediate dominators chain and find common dominator node.
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DomTreeNode *IDomB = NodeB->getIDom();
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while(IDomB) {
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if (NodeADoms.count(IDomB) != 0)
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return IDomB->getBlock();
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IDomB = IDomB->getIDom();
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}
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return NULL;
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}
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void DomTreeNode::setIDom(DomTreeNode *NewIDom) {
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assert(IDom && "No immediate dominator?");
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if (IDom != NewIDom) {
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std::vector<DomTreeNode*>::iterator I =
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std::find(IDom->Children.begin(), IDom->Children.end(), this);
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assert(I != IDom->Children.end() &&
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"Not in immediate dominator children set!");
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// I am no longer your child...
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IDom->Children.erase(I);
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// Switch to new dominator
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IDom = NewIDom;
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IDom->Children.push_back(this);
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}
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}
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static std::ostream &operator<<(std::ostream &o, const DomTreeNode *Node) {
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if (Node->getBlock())
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WriteAsOperand(o, Node->getBlock(), false);
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else
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o << " <<exit node>>";
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o << " {" << Node->getDFSNumIn() << "," << Node->getDFSNumOut() << "}";
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return o << "\n";
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}
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static void PrintDomTree(const DomTreeNode *N, std::ostream &o,
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unsigned Lev) {
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o << std::string(2*Lev, ' ') << "[" << Lev << "] " << N;
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for (DomTreeNode::const_iterator I = N->begin(), E = N->end();
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I != E; ++I)
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PrintDomTree(*I, o, Lev+1);
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}
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/// eraseNode - Removes a node from the domiantor tree. Block must not
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/// domiante any other blocks. Removes node from its immediate dominator's
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/// children list. Deletes dominator node associated with basic block BB.
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void DominatorTreeBase::eraseNode(BasicBlock *BB) {
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DomTreeNode *Node = getNode(BB);
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assert (Node && "Removing node that isn't in dominator tree.");
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assert (Node->getChildren().empty() && "Node is not a leaf node.");
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// Remove node from immediate dominator's children list.
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DomTreeNode *IDom = Node->getIDom();
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if (IDom) {
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std::vector<DomTreeNode*>::iterator I =
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std::find(IDom->Children.begin(), IDom->Children.end(), Node);
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assert(I != IDom->Children.end() &&
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"Not in immediate dominator children set!");
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// I am no longer your child...
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IDom->Children.erase(I);
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}
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DomTreeNodes.erase(BB);
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delete Node;
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}
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void DominatorTreeBase::print(std::ostream &o, const Module* ) const {
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o << "=============================--------------------------------\n";
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o << "Inorder Dominator Tree: ";
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if (DFSInfoValid)
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o << "DFSNumbers invalid: " << SlowQueries << " slow queries.";
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o << "\n";
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PrintDomTree(getRootNode(), o, 1);
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}
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void DominatorTreeBase::dump() {
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print(llvm::cerr);
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}
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bool DominatorTree::runOnFunction(Function &F) {
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reset(); // Reset from the last time we were run...
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// Initialize roots
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Roots.push_back(&F.getEntryBlock());
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IDoms[&F.getEntryBlock()] = 0;
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DomTreeNodes[&F.getEntryBlock()] = 0;
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Vertex.push_back(0);
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Calculate<BasicBlock*>(*this, F);
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updateDFSNumbers();
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return false;
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}
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//===----------------------------------------------------------------------===//
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// DominanceFrontier Implementation
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//===----------------------------------------------------------------------===//
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char DominanceFrontier::ID = 0;
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static RegisterPass<DominanceFrontier>
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G("domfrontier", "Dominance Frontier Construction", true);
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// NewBB is split and now it has one successor. Update dominace frontier to
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// reflect this change.
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void DominanceFrontier::splitBlock(BasicBlock *NewBB) {
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assert(NewBB->getTerminator()->getNumSuccessors() == 1
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&& "NewBB should have a single successor!");
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BasicBlock *NewBBSucc = NewBB->getTerminator()->getSuccessor(0);
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std::vector<BasicBlock*> PredBlocks;
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for (pred_iterator PI = pred_begin(NewBB), PE = pred_end(NewBB);
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PI != PE; ++PI)
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PredBlocks.push_back(*PI);
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if (PredBlocks.empty())
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// If NewBB does not have any predecessors then it is a entry block.
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// In this case, NewBB and its successor NewBBSucc dominates all
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// other blocks.
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return;
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// NewBBSucc inherits original NewBB frontier.
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DominanceFrontier::iterator NewBBI = find(NewBB);
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if (NewBBI != end()) {
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DominanceFrontier::DomSetType NewBBSet = NewBBI->second;
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DominanceFrontier::DomSetType NewBBSuccSet;
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NewBBSuccSet.insert(NewBBSet.begin(), NewBBSet.end());
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addBasicBlock(NewBBSucc, NewBBSuccSet);
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}
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// If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
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// DF(PredBlocks[0]) without the stuff that the new block does not dominate
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// a predecessor of.
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DominatorTree &DT = getAnalysis<DominatorTree>();
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if (DT.dominates(NewBB, NewBBSucc)) {
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DominanceFrontier::iterator DFI = find(PredBlocks[0]);
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if (DFI != end()) {
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DominanceFrontier::DomSetType Set = DFI->second;
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// Filter out stuff in Set that we do not dominate a predecessor of.
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for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
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E = Set.end(); SetI != E;) {
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bool DominatesPred = false;
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for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
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PI != E; ++PI)
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if (DT.dominates(NewBB, *PI))
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DominatesPred = true;
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if (!DominatesPred)
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Set.erase(SetI++);
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else
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++SetI;
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}
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if (NewBBI != end()) {
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for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
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E = Set.end(); SetI != E; ++SetI) {
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BasicBlock *SB = *SetI;
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addToFrontier(NewBBI, SB);
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}
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} else
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addBasicBlock(NewBB, Set);
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}
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} else {
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// DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
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// NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
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// NewBBSucc)). NewBBSucc is the single successor of NewBB.
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DominanceFrontier::DomSetType NewDFSet;
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NewDFSet.insert(NewBBSucc);
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addBasicBlock(NewBB, NewDFSet);
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}
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// Now we must loop over all of the dominance frontiers in the function,
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// replacing occurrences of NewBBSucc with NewBB in some cases. All
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// blocks that dominate a block in PredBlocks and contained NewBBSucc in
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// their dominance frontier must be updated to contain NewBB instead.
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//
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for (Function::iterator FI = NewBB->getParent()->begin(),
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FE = NewBB->getParent()->end(); FI != FE; ++FI) {
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DominanceFrontier::iterator DFI = find(FI);
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if (DFI == end()) continue; // unreachable block.
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// Only consider nodes that have NewBBSucc in their dominator frontier.
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if (!DFI->second.count(NewBBSucc)) continue;
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// Verify whether this block dominates a block in predblocks. If not, do
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// not update it.
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bool BlockDominatesAny = false;
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for (std::vector<BasicBlock*>::const_iterator BI = PredBlocks.begin(),
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BE = PredBlocks.end(); BI != BE; ++BI) {
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if (DT.dominates(FI, *BI)) {
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BlockDominatesAny = true;
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break;
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}
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}
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if (!BlockDominatesAny)
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continue;
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// If NewBBSucc should not stay in our dominator frontier, remove it.
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// We remove it unless there is a predecessor of NewBBSucc that we
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// dominate, but we don't strictly dominate NewBBSucc.
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bool ShouldRemove = true;
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if ((BasicBlock*)FI == NewBBSucc || !DT.dominates(FI, NewBBSucc)) {
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// Okay, we know that PredDom does not strictly dominate NewBBSucc.
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// Check to see if it dominates any predecessors of NewBBSucc.
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for (pred_iterator PI = pred_begin(NewBBSucc),
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E = pred_end(NewBBSucc); PI != E; ++PI)
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if (DT.dominates(FI, *PI)) {
|
|
ShouldRemove = false;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (ShouldRemove)
|
|
removeFromFrontier(DFI, NewBBSucc);
|
|
addToFrontier(DFI, NewBB);
|
|
}
|
|
}
|
|
|
|
namespace {
|
|
class DFCalculateWorkObject {
|
|
public:
|
|
DFCalculateWorkObject(BasicBlock *B, BasicBlock *P,
|
|
const DomTreeNode *N,
|
|
const DomTreeNode *PN)
|
|
: currentBB(B), parentBB(P), Node(N), parentNode(PN) {}
|
|
BasicBlock *currentBB;
|
|
BasicBlock *parentBB;
|
|
const DomTreeNode *Node;
|
|
const DomTreeNode *parentNode;
|
|
};
|
|
}
|
|
|
|
const DominanceFrontier::DomSetType &
|
|
DominanceFrontier::calculate(const DominatorTree &DT,
|
|
const DomTreeNode *Node) {
|
|
BasicBlock *BB = Node->getBlock();
|
|
DomSetType *Result = NULL;
|
|
|
|
std::vector<DFCalculateWorkObject> workList;
|
|
SmallPtrSet<BasicBlock *, 32> visited;
|
|
|
|
workList.push_back(DFCalculateWorkObject(BB, NULL, Node, NULL));
|
|
do {
|
|
DFCalculateWorkObject *currentW = &workList.back();
|
|
assert (currentW && "Missing work object.");
|
|
|
|
BasicBlock *currentBB = currentW->currentBB;
|
|
BasicBlock *parentBB = currentW->parentBB;
|
|
const DomTreeNode *currentNode = currentW->Node;
|
|
const DomTreeNode *parentNode = currentW->parentNode;
|
|
assert (currentBB && "Invalid work object. Missing current Basic Block");
|
|
assert (currentNode && "Invalid work object. Missing current Node");
|
|
DomSetType &S = Frontiers[currentBB];
|
|
|
|
// Visit each block only once.
|
|
if (visited.count(currentBB) == 0) {
|
|
visited.insert(currentBB);
|
|
|
|
// Loop over CFG successors to calculate DFlocal[currentNode]
|
|
for (succ_iterator SI = succ_begin(currentBB), SE = succ_end(currentBB);
|
|
SI != SE; ++SI) {
|
|
// Does Node immediately dominate this successor?
|
|
if (DT[*SI]->getIDom() != currentNode)
|
|
S.insert(*SI);
|
|
}
|
|
}
|
|
|
|
// At this point, S is DFlocal. Now we union in DFup's of our children...
|
|
// Loop through and visit the nodes that Node immediately dominates (Node's
|
|
// children in the IDomTree)
|
|
bool visitChild = false;
|
|
for (DomTreeNode::const_iterator NI = currentNode->begin(),
|
|
NE = currentNode->end(); NI != NE; ++NI) {
|
|
DomTreeNode *IDominee = *NI;
|
|
BasicBlock *childBB = IDominee->getBlock();
|
|
if (visited.count(childBB) == 0) {
|
|
workList.push_back(DFCalculateWorkObject(childBB, currentBB,
|
|
IDominee, currentNode));
|
|
visitChild = true;
|
|
}
|
|
}
|
|
|
|
// If all children are visited or there is any child then pop this block
|
|
// from the workList.
|
|
if (!visitChild) {
|
|
|
|
if (!parentBB) {
|
|
Result = &S;
|
|
break;
|
|
}
|
|
|
|
DomSetType::const_iterator CDFI = S.begin(), CDFE = S.end();
|
|
DomSetType &parentSet = Frontiers[parentBB];
|
|
for (; CDFI != CDFE; ++CDFI) {
|
|
if (!DT.properlyDominates(parentNode, DT[*CDFI]))
|
|
parentSet.insert(*CDFI);
|
|
}
|
|
workList.pop_back();
|
|
}
|
|
|
|
} while (!workList.empty());
|
|
|
|
return *Result;
|
|
}
|
|
|
|
void DominanceFrontierBase::print(std::ostream &o, const Module* ) const {
|
|
for (const_iterator I = begin(), E = end(); I != E; ++I) {
|
|
o << " DomFrontier for BB";
|
|
if (I->first)
|
|
WriteAsOperand(o, I->first, false);
|
|
else
|
|
o << " <<exit node>>";
|
|
o << " is:\t" << I->second << "\n";
|
|
}
|
|
}
|
|
|
|
void DominanceFrontierBase::dump() {
|
|
print (llvm::cerr);
|
|
}
|