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//===- llvm/CodeGen/MachineLoopInfo.h - Natural Loop Calculator -*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines the MachineLoopInfo class that is used to identify natural
// loops and determine the loop depth of various nodes of the CFG. Note that
// natural loops may actually be several loops that share the same header node.
// This analysis calculates the nesting structure of loops in a function. For
// each natural loop identified, this analysis identifies natural loops
// contained entirely within the loop and the basic blocks the make up the loop.
// It can calculate on the fly various bits of information, for example:
// * whether there is a preheader for the loop
// * the number of back edges to the header
// * whether or not a particular block branches out of the loop
// * the successor blocks of the loop
// * the loop depth
// * the trip count
// * etc...
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/Support/GenericLoopInfo.h"
namespace llvm {
class MachineDominatorTree;
// Implementation in LoopInfoImpl.h
class MachineLoop;
extern template class LoopBase<MachineBasicBlock, MachineLoop>;
class MachineLoop : public LoopBase<MachineBasicBlock, MachineLoop> {
/// Return the "top" block in the loop, which is the first block in the linear
/// layout, ignoring any parts of the loop not contiguous with the part that
/// contains the header.
MachineBasicBlock *getTopBlock();
/// Return the "bottom" block in the loop, which is the last block in the
/// linear layout, ignoring any parts of the loop not contiguous with the part
/// that contains the header.
MachineBasicBlock *getBottomBlock();
/// Find the block that contains the loop control variable and the
/// loop test. This will return the latch block if it's one of the exiting
/// blocks. Otherwise, return the exiting block. Return 'null' when
/// multiple exiting blocks are present.
MachineBasicBlock *findLoopControlBlock();
/// Return the debug location of the start of this loop.
/// This looks for a BB terminating instruction with a known debug
/// location by looking at the preheader and header blocks. If it
/// cannot find a terminating instruction with location information,
/// it returns an unknown location.
DebugLoc getStartLoc() const;
/// Returns true if the instruction is loop invariant.
/// I.e., all virtual register operands are defined outside of the loop,
/// physical registers aren't accessed explicitly, and there are no side
/// effects that aren't captured by the operands or other flags.
bool isLoopInvariant(MachineInstr &I) const;
void dump() const;
friend class LoopInfoBase<MachineBasicBlock, MachineLoop>;
explicit MachineLoop(MachineBasicBlock *MBB)
: LoopBase<MachineBasicBlock, MachineLoop>(MBB) {}
MachineLoop() = default;
// Implementation in LoopInfoImpl.h
extern template class LoopInfoBase<MachineBasicBlock, MachineLoop>;
class MachineLoopInfo : public MachineFunctionPass {
friend class LoopBase<MachineBasicBlock, MachineLoop>;
LoopInfoBase<MachineBasicBlock, MachineLoop> LI;
static char ID; // Pass identification, replacement for typeid
explicit MachineLoopInfo(MachineDominatorTree &MDT)
: MachineFunctionPass(ID) {
MachineLoopInfo(const MachineLoopInfo &) = delete;
MachineLoopInfo &operator=(const MachineLoopInfo &) = delete;
LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
/// Find the block that either is the loop preheader, or could
/// speculatively be used as the preheader. This is e.g. useful to place
/// loop setup code. Code that cannot be speculated should not be placed
/// here. SpeculativePreheader is controlling whether it also tries to
/// find the speculative preheader if the regular preheader is not present.
/// With FindMultiLoopPreheader = false, nullptr will be returned if the found
/// preheader is the preheader of multiple loops.
MachineBasicBlock *
findLoopPreheader(MachineLoop *L, bool SpeculativePreheader = false,
bool FindMultiLoopPreheader = false) const;
/// The iterator interface to the top-level loops in the current function.
using iterator = LoopInfoBase<MachineBasicBlock, MachineLoop>::iterator;
inline iterator begin() const { return LI.begin(); }
inline iterator end() const { return LI.end(); }
bool empty() const { return LI.empty(); }
/// Return the innermost loop that BB lives in. If a basic block is in no loop
/// (for example the entry node), null is returned.
inline MachineLoop *getLoopFor(const MachineBasicBlock *BB) const {
return LI.getLoopFor(BB);
/// Same as getLoopFor.
inline const MachineLoop *operator[](const MachineBasicBlock *BB) const {
return LI.getLoopFor(BB);
/// Return the loop nesting level of the specified block.
inline unsigned getLoopDepth(const MachineBasicBlock *BB) const {
return LI.getLoopDepth(BB);
/// True if the block is a loop header node.
inline bool isLoopHeader(const MachineBasicBlock *BB) const {
return LI.isLoopHeader(BB);
/// Calculate the natural loop information.
bool runOnMachineFunction(MachineFunction &F) override;
void calculate(MachineDominatorTree &MDT);
void releaseMemory() override { LI.releaseMemory(); }
void getAnalysisUsage(AnalysisUsage &AU) const override;
/// This removes the specified top-level loop from this loop info object. The
/// loop is not deleted, as it will presumably be inserted into another loop.
inline MachineLoop *removeLoop(iterator I) { return LI.removeLoop(I); }
/// Change the top-level loop that contains BB to the specified loop. This
/// should be used by transformations that restructure the loop hierarchy
/// tree.
inline void changeLoopFor(MachineBasicBlock *BB, MachineLoop *L) {
LI.changeLoopFor(BB, L);
/// Replace the specified loop in the top-level loops list with the indicated
/// loop.
inline void changeTopLevelLoop(MachineLoop *OldLoop, MachineLoop *NewLoop) {
LI.changeTopLevelLoop(OldLoop, NewLoop);
/// This adds the specified loop to the collection of top-level loops.
inline void addTopLevelLoop(MachineLoop *New) {
/// This method completely removes BB from all data structures, including all
/// of the Loop objects it is nested in and our mapping from
/// MachineBasicBlocks to loops.
void removeBlock(MachineBasicBlock *BB) {
// Allow clients to walk the list of nested loops...
template <> struct GraphTraits<const MachineLoop*> {
using NodeRef = const MachineLoop *;
using ChildIteratorType = MachineLoopInfo::iterator;
static NodeRef getEntryNode(const MachineLoop *L) { return L; }
static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
static ChildIteratorType child_end(NodeRef N) { return N->end(); }
template <> struct GraphTraits<MachineLoop*> {
using NodeRef = MachineLoop *;
using ChildIteratorType = MachineLoopInfo::iterator;
static NodeRef getEntryNode(MachineLoop *L) { return L; }
static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
static ChildIteratorType child_end(NodeRef N) { return N->end(); }
} // end namespace llvm