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https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11015 91177308-0d34-0410-b5e6-96231b3b80d8
374 lines
14 KiB
C++
374 lines
14 KiB
C++
//===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
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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 defines the LoopInfo class that is used to identify natural loops
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// and determine the loop depth of various nodes of the CFG. Note that the
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// loops identified may actually be several natural loops that share the same
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// header node... not just a single natural loop.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Assembly/Writer.h"
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#include "llvm/Support/CFG.h"
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#include "Support/DepthFirstIterator.h"
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#include <algorithm>
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namespace llvm {
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static RegisterAnalysis<LoopInfo>
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X("loops", "Natural Loop Construction", true);
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//===----------------------------------------------------------------------===//
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// Loop implementation
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//
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bool Loop::contains(const BasicBlock *BB) const {
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return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
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}
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bool Loop::isLoopExit(const BasicBlock *BB) const {
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for (succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
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SI != SE; ++SI) {
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if (!contains(*SI))
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return true;
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}
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return false;
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}
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/// getNumBackEdges - Calculate the number of back edges to the loop header.
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///
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unsigned Loop::getNumBackEdges() const {
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unsigned NumBackEdges = 0;
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BasicBlock *H = getHeader();
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for (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I)
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if (contains(*I))
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++NumBackEdges;
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return NumBackEdges;
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}
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void Loop::print(std::ostream &OS, unsigned Depth) const {
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OS << std::string(Depth*2, ' ') << "Loop Containing: ";
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for (unsigned i = 0; i < getBlocks().size(); ++i) {
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if (i) OS << ",";
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WriteAsOperand(OS, getBlocks()[i], false);
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}
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if (!ExitBlocks.empty()) {
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OS << "\tExitBlocks: ";
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for (unsigned i = 0; i < getExitBlocks().size(); ++i) {
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if (i) OS << ",";
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WriteAsOperand(OS, getExitBlocks()[i], false);
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}
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}
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OS << "\n";
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for (iterator I = begin(), E = end(); I != E; ++I)
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(*I)->print(OS, Depth+2);
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}
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void Loop::dump() const {
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print(std::cerr);
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}
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//===----------------------------------------------------------------------===//
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// LoopInfo implementation
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//
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void LoopInfo::stub() {}
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bool LoopInfo::runOnFunction(Function &) {
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releaseMemory();
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Calculate(getAnalysis<DominatorSet>()); // Update
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return false;
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}
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void LoopInfo::releaseMemory() {
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for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
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E = TopLevelLoops.end(); I != E; ++I)
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delete *I; // Delete all of the loops...
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BBMap.clear(); // Reset internal state of analysis
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TopLevelLoops.clear();
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}
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void LoopInfo::Calculate(const DominatorSet &DS) {
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BasicBlock *RootNode = DS.getRoot();
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for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
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NE = df_end(RootNode); NI != NE; ++NI)
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if (Loop *L = ConsiderForLoop(*NI, DS))
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TopLevelLoops.push_back(L);
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for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
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TopLevelLoops[i]->setLoopDepth(1);
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}
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void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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AU.addRequired<DominatorSet>();
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}
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void LoopInfo::print(std::ostream &OS) const {
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for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
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TopLevelLoops[i]->print(OS);
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#if 0
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for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
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E = BBMap.end(); I != E; ++I)
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OS << "BB '" << I->first->getName() << "' level = "
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<< I->second->LoopDepth << "\n";
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#endif
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}
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static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
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if (SubLoop == 0) return true;
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if (SubLoop == ParentLoop) return false;
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return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
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}
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Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
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if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
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std::vector<BasicBlock *> TodoStack;
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// Scan the predecessors of BB, checking to see if BB dominates any of
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// them. This identifies backedges which target this node...
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for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
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if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
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TodoStack.push_back(*I);
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if (TodoStack.empty()) return 0; // No backedges to this block...
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// Create a new loop to represent this basic block...
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Loop *L = new Loop(BB);
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BBMap[BB] = L;
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BasicBlock *EntryBlock = &BB->getParent()->getEntryBlock();
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while (!TodoStack.empty()) { // Process all the nodes in the loop
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BasicBlock *X = TodoStack.back();
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TodoStack.pop_back();
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if (!L->contains(X) && // As of yet unprocessed??
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DS.dominates(EntryBlock, X)) { // X is reachable from entry block?
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// Check to see if this block already belongs to a loop. If this occurs
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// then we have a case where a loop that is supposed to be a child of the
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// current loop was processed before the current loop. When this occurs,
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// this child loop gets added to a part of the current loop, making it a
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// sibling to the current loop. We have to reparent this loop.
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if (Loop *SubLoop = const_cast<Loop*>(getLoopFor(X)))
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if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) {
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// Remove the subloop from it's current parent...
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assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
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Loop *SLP = SubLoop->ParentLoop; // SubLoopParent
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std::vector<Loop*>::iterator I =
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std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
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assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?");
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SLP->SubLoops.erase(I); // Remove from parent...
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// Add the subloop to THIS loop...
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SubLoop->ParentLoop = L;
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L->SubLoops.push_back(SubLoop);
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}
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// Normal case, add the block to our loop...
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L->Blocks.push_back(X);
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// Add all of the predecessors of X to the end of the work stack...
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TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
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}
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}
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// If there are any loops nested within this loop, create them now!
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for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
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E = L->Blocks.end(); I != E; ++I)
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if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
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L->SubLoops.push_back(NewLoop);
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NewLoop->ParentLoop = L;
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}
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// Add the basic blocks that comprise this loop to the BBMap so that this
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// loop can be found for them.
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//
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for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
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E = L->Blocks.end(); I != E; ++I) {
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std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
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if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet...
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BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
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}
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// Now that we have a list of all of the child loops of this loop, check to
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// see if any of them should actually be nested inside of each other. We can
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// accidentally pull loops our of their parents, so we must make sure to
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// organize the loop nests correctly now.
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{
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std::map<BasicBlock*, Loop*> ContainingLoops;
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for (unsigned i = 0; i != L->SubLoops.size(); ++i) {
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Loop *Child = L->SubLoops[i];
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assert(Child->getParentLoop() == L && "Not proper child loop?");
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if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) {
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// If there is already a loop which contains this loop, move this loop
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// into the containing loop.
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MoveSiblingLoopInto(Child, ContainingLoop);
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--i; // The loop got removed from the SubLoops list.
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} else {
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// This is currently considered to be a top-level loop. Check to see if
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// any of the contained blocks are loop headers for subloops we have
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// already processed.
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for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) {
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Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]];
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if (BlockLoop == 0) { // Child block not processed yet...
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BlockLoop = Child;
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} else if (BlockLoop != Child) {
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Loop *SubLoop = BlockLoop;
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// Reparent all of the blocks which used to belong to BlockLoops
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for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j)
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ContainingLoops[SubLoop->Blocks[j]] = Child;
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// There is already a loop which contains this block, that means
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// that we should reparent the loop which the block is currently
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// considered to belong to to be a child of this loop.
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MoveSiblingLoopInto(SubLoop, Child);
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--i; // We just shrunk the SubLoops list.
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}
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}
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}
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}
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}
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// Now that we know all of the blocks that make up this loop, see if there are
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// any branches to outside of the loop... building the ExitBlocks list.
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for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
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BE = L->Blocks.end(); BI != BE; ++BI)
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for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
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if (!L->contains(*I)) // Not in current loop?
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L->ExitBlocks.push_back(*I); // It must be an exit block...
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return L;
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}
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/// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of
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/// the NewParent Loop, instead of being a sibling of it.
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void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) {
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Loop *OldParent = NewChild->getParentLoop();
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assert(OldParent && OldParent == NewParent->getParentLoop() &&
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NewChild != NewParent && "Not sibling loops!");
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// Remove NewChild from being a child of OldParent
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std::vector<Loop*>::iterator I =
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std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild);
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assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
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OldParent->SubLoops.erase(I); // Remove from parent's subloops list
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NewChild->ParentLoop = 0;
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InsertLoopInto(NewChild, NewParent);
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}
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/// InsertLoopInto - This inserts loop L into the specified parent loop. If the
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/// parent loop contains a loop which should contain L, the loop gets inserted
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/// into L instead.
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void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) {
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BasicBlock *LHeader = L->getHeader();
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assert(Parent->contains(LHeader) && "This loop should not be inserted here!");
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// Check to see if it belongs in a child loop...
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for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i)
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if (Parent->SubLoops[i]->contains(LHeader)) {
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InsertLoopInto(L, Parent->SubLoops[i]);
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return;
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}
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// If not, insert it here!
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Parent->SubLoops.push_back(L);
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L->ParentLoop = Parent;
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}
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/// getLoopPreheader - If there is a preheader for this loop, return it. A
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/// loop has a preheader if there is only one edge to the header of the loop
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/// from outside of the loop. If this is the case, the block branching to the
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/// header of the loop is the preheader node. The "preheaders" pass can be
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/// "Required" to ensure that there is always a preheader node for every loop.
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///
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/// This method returns null if there is no preheader for the loop (either
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/// because the loop is dead or because multiple blocks branch to the header
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/// node of this loop).
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///
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BasicBlock *Loop::getLoopPreheader() const {
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// Keep track of nodes outside the loop branching to the header...
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BasicBlock *Out = 0;
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// Loop over the predecessors of the header node...
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BasicBlock *Header = getHeader();
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for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
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PI != PE; ++PI)
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if (!contains(*PI)) { // If the block is not in the loop...
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if (Out && Out != *PI)
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return 0; // Multiple predecessors outside the loop
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Out = *PI;
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}
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// Make sure there is only one exit out of the preheader...
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succ_iterator SI = succ_begin(Out);
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++SI;
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if (SI != succ_end(Out))
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return 0; // Multiple exits from the block, must not be a preheader.
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// If there is exactly one preheader, return it. If there was zero, then Out
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// is still null.
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return Out;
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}
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/// addBasicBlockToLoop - This function is used by other analyses to update loop
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/// information. NewBB is set to be a new member of the current loop. Because
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/// of this, it is added as a member of all parent loops, and is added to the
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/// specified LoopInfo object as being in the current basic block. It is not
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/// valid to replace the loop header with this method.
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///
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void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
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assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
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assert(NewBB && "Cannot add a null basic block to the loop!");
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assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
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// Add the loop mapping to the LoopInfo object...
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LI.BBMap[NewBB] = this;
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// Add the basic block to this loop and all parent loops...
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Loop *L = this;
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while (L) {
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L->Blocks.push_back(NewBB);
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L = L->getParentLoop();
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}
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}
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/// changeExitBlock - This method is used to update loop information. All
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/// instances of the specified Old basic block are removed from the exit list
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/// and replaced with New.
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///
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void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) {
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assert(Old != New && "Cannot changeExitBlock to the same thing!");
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assert(Old && New && "Cannot changeExitBlock to or from a null node!");
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assert(hasExitBlock(Old) && "Old exit block not found!");
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std::vector<BasicBlock*>::iterator
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I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
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while (I != ExitBlocks.end()) {
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*I = New;
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I = std::find(I+1, ExitBlocks.end(), Old);
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}
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}
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} // End llvm namespace
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