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llvm/lib/CodeGen/MachineOutliner.cpp
Serge Guelton 9d54400bba Module::getOrInsertFunction is using C-style vararg instead of variadic templates. 
From a user prospective, it forces the use of an annoying nullptr to mark the end of the vararg, and there's not type checking on the arguments.
The variadic template is an obvious solution to both issues.

Differential Revision: https://reviews.llvm.org/D31070



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@299949 91177308-0d34-0410-b5e6-96231b3b80d8
2017-04-11 15:01:18 +00:00

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//===---- MachineOutliner.cpp - Outline instructions -----------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// Replaces repeated sequences of instructions with function calls.
///
/// This works by placing every instruction from every basic block in a
/// suffix tree, and repeatedly querying that tree for repeated sequences of
/// instructions. If a sequence of instructions appears often, then it ought
/// to be beneficial to pull out into a function.
///
/// This was originally presented at the 2016 LLVM Developers' Meeting in the
/// talk "Reducing Code Size Using Outlining". For a high-level overview of
/// how this pass works, the talk is available on YouTube at
///
/// https://www.youtube.com/watch?v=yorld-WSOeU
///
/// The slides for the talk are available at
///
/// http://www.llvm.org/devmtg/2016-11/Slides/Paquette-Outliner.pdf
///
/// The talk provides an overview of how the outliner finds candidates and
/// ultimately outlines them. It describes how the main data structure for this
/// pass, the suffix tree, is queried and purged for candidates. It also gives
/// a simplified suffix tree construction algorithm for suffix trees based off
/// of the algorithm actually used here, Ukkonen's algorithm.
///
/// For the original RFC for this pass, please see
///
/// http://lists.llvm.org/pipermail/llvm-dev/2016-August/104170.html
///
/// For more information on the suffix tree data structure, please see
/// https://www.cs.helsinki.fi/u/ukkonen/SuffixT1withFigs.pdf
///
//===----------------------------------------------------------------------===//
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/Twine.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
#include <functional>
#include <map>
#include <sstream>
#include <tuple>
#include <vector>
#define DEBUG_TYPE "machine-outliner"
using namespace llvm;
STATISTIC(NumOutlined, "Number of candidates outlined");
STATISTIC(FunctionsCreated, "Number of functions created");
namespace {
/// \brief An individual sequence of instructions to be replaced with a call to
/// an outlined function.
struct Candidate {
/// Set to false if the candidate overlapped with another candidate.
bool InCandidateList = true;
/// The start index of this \p Candidate.
size_t StartIdx;
/// The number of instructions in this \p Candidate.
size_t Len;
/// The index of this \p Candidate's \p OutlinedFunction in the list of
/// \p OutlinedFunctions.
size_t FunctionIdx;
/// \brief The number of instructions that would be saved by outlining every
/// candidate of this type.
///
/// This is a fixed value which is not updated during the candidate pruning
/// process. It is only used for deciding which candidate to keep if two
/// candidates overlap. The true benefit is stored in the OutlinedFunction
/// for some given candidate.
unsigned Benefit = 0;
Candidate(size_t StartIdx, size_t Len, size_t FunctionIdx)
: StartIdx(StartIdx), Len(Len), FunctionIdx(FunctionIdx) {}
Candidate() {}
/// \brief Used to ensure that \p Candidates are outlined in an order that
/// preserves the start and end indices of other \p Candidates.
bool operator<(const Candidate &RHS) const { return StartIdx > RHS.StartIdx; }
};
/// \brief The information necessary to create an outlined function for some
/// class of candidate.
struct OutlinedFunction {
/// The actual outlined function created.
/// This is initialized after we go through and create the actual function.
MachineFunction *MF = nullptr;
/// A number assigned to this function which appears at the end of its name.
size_t Name;
/// The number of candidates for this OutlinedFunction.
size_t OccurrenceCount = 0;
/// \brief The sequence of integers corresponding to the instructions in this
/// function.
std::vector<unsigned> Sequence;
/// The number of instructions this function would save.
unsigned Benefit = 0;
/// \brief Set to true if candidates for this outlined function should be
/// replaced with tail calls to this OutlinedFunction.
bool IsTailCall = false;
OutlinedFunction(size_t Name, size_t OccurrenceCount,
const std::vector<unsigned> &Sequence,
unsigned Benefit, bool IsTailCall)
: Name(Name), OccurrenceCount(OccurrenceCount), Sequence(Sequence),
Benefit(Benefit), IsTailCall(IsTailCall)
{}
};
/// Represents an undefined index in the suffix tree.
const size_t EmptyIdx = -1;
/// A node in a suffix tree which represents a substring or suffix.
///
/// Each node has either no children or at least two children, with the root
/// being a exception in the empty tree.
///
/// Children are represented as a map between unsigned integers and nodes. If
/// a node N has a child M on unsigned integer k, then the mapping represented
/// by N is a proper prefix of the mapping represented by M. Note that this,
/// although similar to a trie is somewhat different: each node stores a full
/// substring of the full mapping rather than a single character state.
///
/// Each internal node contains a pointer to the internal node representing
/// the same string, but with the first character chopped off. This is stored
/// in \p Link. Each leaf node stores the start index of its respective
/// suffix in \p SuffixIdx.
struct SuffixTreeNode {
/// The children of this node.
///
/// A child existing on an unsigned integer implies that from the mapping
/// represented by the current node, there is a way to reach another
/// mapping by tacking that character on the end of the current string.
DenseMap<unsigned, SuffixTreeNode *> Children;
/// A flag set to false if the node has been pruned from the tree.
bool IsInTree = true;
/// The start index of this node's substring in the main string.
size_t StartIdx = EmptyIdx;
/// The end index of this node's substring in the main string.
///
/// Every leaf node must have its \p EndIdx incremented at the end of every
/// step in the construction algorithm. To avoid having to update O(N)
/// nodes individually at the end of every step, the end index is stored
/// as a pointer.
size_t *EndIdx = nullptr;
/// For leaves, the start index of the suffix represented by this node.
///
/// For all other nodes, this is ignored.
size_t SuffixIdx = EmptyIdx;
/// \brief For internal nodes, a pointer to the internal node representing
/// the same sequence with the first character chopped off.
///
/// This has two major purposes in the suffix tree. The first is as a
/// shortcut in Ukkonen's construction algorithm. One of the things that
/// Ukkonen's algorithm does to achieve linear-time construction is
/// keep track of which node the next insert should be at. This makes each
/// insert O(1), and there are a total of O(N) inserts. The suffix link
/// helps with inserting children of internal nodes.
///
/// Say we add a child to an internal node with associated mapping S. The
/// next insertion must be at the node representing S - its first character.
/// This is given by the way that we iteratively build the tree in Ukkonen's
/// algorithm. The main idea is to look at the suffixes of each prefix in the
/// string, starting with the longest suffix of the prefix, and ending with
/// the shortest. Therefore, if we keep pointers between such nodes, we can
/// move to the next insertion point in O(1) time. If we don't, then we'd
/// have to query from the root, which takes O(N) time. This would make the
/// construction algorithm O(N^2) rather than O(N).
///
/// The suffix link is also used during the tree pruning process to let us
/// quickly throw out a bunch of potential overlaps. Say we have a sequence
/// S we want to outline. Then each of its suffixes contribute to at least
/// one overlapping case. Therefore, we can follow the suffix links
/// starting at the node associated with S to the root and "delete" those
/// nodes, save for the root. For each candidate, this removes
/// O(|candidate|) overlaps from the search space. We don't actually
/// completely invalidate these nodes though; doing that is far too
/// aggressive. Consider the following pathological string:
///
/// 1 2 3 1 2 3 2 3 2 3 2 3 2 3 2 3 2 3
///
/// If we, for the sake of example, outlined 1 2 3, then we would throw
/// out all instances of 2 3. This isn't desirable. To get around this,
/// when we visit a link node, we decrement its occurrence count by the
/// number of sequences we outlined in the current step. In the pathological
/// example, the 2 3 node would have an occurrence count of 8, while the
/// 1 2 3 node would have an occurrence count of 2. Thus, the 2 3 node
/// would survive to the next round allowing us to outline the extra
/// instances of 2 3.
SuffixTreeNode *Link = nullptr;
/// The parent of this node. Every node except for the root has a parent.
SuffixTreeNode *Parent = nullptr;
/// The number of times this node's string appears in the tree.
///
/// This is equal to the number of leaf children of the string. It represents
/// the number of suffixes that the node's string is a prefix of.
size_t OccurrenceCount = 0;
/// The length of the string formed by concatenating the edge labels from the
/// root to this node.
size_t ConcatLen = 0;
/// Returns true if this node is a leaf.
bool isLeaf() const { return SuffixIdx != EmptyIdx; }
/// Returns true if this node is the root of its owning \p SuffixTree.
bool isRoot() const { return StartIdx == EmptyIdx; }
/// Return the number of elements in the substring associated with this node.
size_t size() const {
// Is it the root? If so, it's the empty string so return 0.
if (isRoot())
return 0;
assert(*EndIdx != EmptyIdx && "EndIdx is undefined!");
// Size = the number of elements in the string.
// For example, [0 1 2 3] has length 4, not 3. 3-0 = 3, so we have 3-0+1.
return *EndIdx - StartIdx + 1;
}
SuffixTreeNode(size_t StartIdx, size_t *EndIdx, SuffixTreeNode *Link,
SuffixTreeNode *Parent)
: StartIdx(StartIdx), EndIdx(EndIdx), Link(Link), Parent(Parent) {}
SuffixTreeNode() {}
};
/// A data structure for fast substring queries.
///
/// Suffix trees represent the suffixes of their input strings in their leaves.
/// A suffix tree is a type of compressed trie structure where each node
/// represents an entire substring rather than a single character. Each leaf
/// of the tree is a suffix.
///
/// A suffix tree can be seen as a type of state machine where each state is a
/// substring of the full string. The tree is structured so that, for a string
/// of length N, there are exactly N leaves in the tree. This structure allows
/// us to quickly find repeated substrings of the input string.
///
/// In this implementation, a "string" is a vector of unsigned integers.
/// These integers may result from hashing some data type. A suffix tree can
/// contain 1 or many strings, which can then be queried as one large string.
///
/// The suffix tree is implemented using Ukkonen's algorithm for linear-time
/// suffix tree construction. Ukkonen's algorithm is explained in more detail
/// in the paper by Esko Ukkonen "On-line construction of suffix trees. The
/// paper is available at
///
/// https://www.cs.helsinki.fi/u/ukkonen/SuffixT1withFigs.pdf
class SuffixTree {
private:
/// Each element is an integer representing an instruction in the module.
ArrayRef<unsigned> Str;
/// Maintains each node in the tree.
SpecificBumpPtrAllocator<SuffixTreeNode> NodeAllocator;
/// The root of the suffix tree.
///
/// The root represents the empty string. It is maintained by the
/// \p NodeAllocator like every other node in the tree.
SuffixTreeNode *Root = nullptr;
/// Stores each leaf node in the tree.
///
/// This is used for finding outlining candidates.
std::vector<SuffixTreeNode *> LeafVector;
/// Maintains the end indices of the internal nodes in the tree.
///
/// Each internal node is guaranteed to never have its end index change
/// during the construction algorithm; however, leaves must be updated at
/// every step. Therefore, we need to store leaf end indices by reference
/// to avoid updating O(N) leaves at every step of construction. Thus,
/// every internal node must be allocated its own end index.
BumpPtrAllocator InternalEndIdxAllocator;
/// The end index of each leaf in the tree.
size_t LeafEndIdx = -1;
/// \brief Helper struct which keeps track of the next insertion point in
/// Ukkonen's algorithm.
struct ActiveState {
/// The next node to insert at.
SuffixTreeNode *Node;
/// The index of the first character in the substring currently being added.
size_t Idx = EmptyIdx;
/// The length of the substring we have to add at the current step.
size_t Len = 0;
};
/// \brief The point the next insertion will take place at in the
/// construction algorithm.
ActiveState Active;
/// Allocate a leaf node and add it to the tree.
///
/// \param Parent The parent of this node.
/// \param StartIdx The start index of this node's associated string.
/// \param Edge The label on the edge leaving \p Parent to this node.
///
/// \returns A pointer to the allocated leaf node.
SuffixTreeNode *insertLeaf(SuffixTreeNode &Parent, size_t StartIdx,
unsigned Edge) {
assert(StartIdx <= LeafEndIdx && "String can't start after it ends!");
SuffixTreeNode *N = new (NodeAllocator.Allocate()) SuffixTreeNode(StartIdx,
&LeafEndIdx,
nullptr,
&Parent);
Parent.Children[Edge] = N;
return N;
}
/// Allocate an internal node and add it to the tree.
///
/// \param Parent The parent of this node. Only null when allocating the root.
/// \param StartIdx The start index of this node's associated string.
/// \param EndIdx The end index of this node's associated string.
/// \param Edge The label on the edge leaving \p Parent to this node.
///
/// \returns A pointer to the allocated internal node.
SuffixTreeNode *insertInternalNode(SuffixTreeNode *Parent, size_t StartIdx,
size_t EndIdx, unsigned Edge) {
assert(StartIdx <= EndIdx && "String can't start after it ends!");
assert(!(!Parent && StartIdx != EmptyIdx) &&
"Non-root internal nodes must have parents!");
size_t *E = new (InternalEndIdxAllocator) size_t(EndIdx);
SuffixTreeNode *N = new (NodeAllocator.Allocate()) SuffixTreeNode(StartIdx,
E,
Root,
Parent);
if (Parent)
Parent->Children[Edge] = N;
return N;
}
/// \brief Set the suffix indices of the leaves to the start indices of their
/// respective suffixes. Also stores each leaf in \p LeafVector at its
/// respective suffix index.
///
/// \param[in] CurrNode The node currently being visited.
/// \param CurrIdx The current index of the string being visited.
void setSuffixIndices(SuffixTreeNode &CurrNode, size_t CurrIdx) {
bool IsLeaf = CurrNode.Children.size() == 0 && !CurrNode.isRoot();
// Store the length of the concatenation of all strings from the root to
// this node.
if (!CurrNode.isRoot()) {
if (CurrNode.ConcatLen == 0)
CurrNode.ConcatLen = CurrNode.size();
if (CurrNode.Parent)
CurrNode.ConcatLen += CurrNode.Parent->ConcatLen;
}
// Traverse the tree depth-first.
for (auto &ChildPair : CurrNode.Children) {
assert(ChildPair.second && "Node had a null child!");
setSuffixIndices(*ChildPair.second,
CurrIdx + ChildPair.second->size());
}
// Is this node a leaf?
if (IsLeaf) {
// If yes, give it a suffix index and bump its parent's occurrence count.
CurrNode.SuffixIdx = Str.size() - CurrIdx;
assert(CurrNode.Parent && "CurrNode had no parent!");
CurrNode.Parent->OccurrenceCount++;
// Store the leaf in the leaf vector for pruning later.
LeafVector[CurrNode.SuffixIdx] = &CurrNode;
}
}
/// \brief Construct the suffix tree for the prefix of the input ending at
/// \p EndIdx.
///
/// Used to construct the full suffix tree iteratively. At the end of each
/// step, the constructed suffix tree is either a valid suffix tree, or a
/// suffix tree with implicit suffixes. At the end of the final step, the
/// suffix tree is a valid tree.
///
/// \param EndIdx The end index of the current prefix in the main string.
/// \param SuffixesToAdd The number of suffixes that must be added
/// to complete the suffix tree at the current phase.
///
/// \returns The number of suffixes that have not been added at the end of
/// this step.
unsigned extend(size_t EndIdx, size_t SuffixesToAdd) {
SuffixTreeNode *NeedsLink = nullptr;
while (SuffixesToAdd > 0) {
// Are we waiting to add anything other than just the last character?
if (Active.Len == 0) {
// If not, then say the active index is the end index.
Active.Idx = EndIdx;
}
assert(Active.Idx <= EndIdx && "Start index can't be after end index!");
// The first character in the current substring we're looking at.
unsigned FirstChar = Str[Active.Idx];
// Have we inserted anything starting with FirstChar at the current node?
if (Active.Node->Children.count(FirstChar) == 0) {
// If not, then we can just insert a leaf and move too the next step.
insertLeaf(*Active.Node, EndIdx, FirstChar);
// The active node is an internal node, and we visited it, so it must
// need a link if it doesn't have one.
if (NeedsLink) {
NeedsLink->Link = Active.Node;
NeedsLink = nullptr;
}
} else {
// There's a match with FirstChar, so look for the point in the tree to
// insert a new node.
SuffixTreeNode *NextNode = Active.Node->Children[FirstChar];
size_t SubstringLen = NextNode->size();
// Is the current suffix we're trying to insert longer than the size of
// the child we want to move to?
if (Active.Len >= SubstringLen) {
// If yes, then consume the characters we've seen and move to the next
// node.
Active.Idx += SubstringLen;
Active.Len -= SubstringLen;
Active.Node = NextNode;
continue;
}
// Otherwise, the suffix we're trying to insert must be contained in the
// next node we want to move to.
unsigned LastChar = Str[EndIdx];
// Is the string we're trying to insert a substring of the next node?
if (Str[NextNode->StartIdx + Active.Len] == LastChar) {
// If yes, then we're done for this step. Remember our insertion point
// and move to the next end index. At this point, we have an implicit
// suffix tree.
if (NeedsLink && !Active.Node->isRoot()) {
NeedsLink->Link = Active.Node;
NeedsLink = nullptr;
}
Active.Len++;
break;
}
// The string we're trying to insert isn't a substring of the next node,
// but matches up to a point. Split the node.
//
// For example, say we ended our search at a node n and we're trying to
// insert ABD. Then we'll create a new node s for AB, reduce n to just
// representing C, and insert a new leaf node l to represent d. This
// allows us to ensure that if n was a leaf, it remains a leaf.
//
// | ABC ---split---> | AB
// n s
// C / \ D
// n l
// The node s from the diagram
SuffixTreeNode *SplitNode =
insertInternalNode(Active.Node,
NextNode->StartIdx,
NextNode->StartIdx + Active.Len - 1,
FirstChar);
// Insert the new node representing the new substring into the tree as
// a child of the split node. This is the node l from the diagram.
insertLeaf(*SplitNode, EndIdx, LastChar);
// Make the old node a child of the split node and update its start
// index. This is the node n from the diagram.
NextNode->StartIdx += Active.Len;
NextNode->Parent = SplitNode;
SplitNode->Children[Str[NextNode->StartIdx]] = NextNode;
// SplitNode is an internal node, update the suffix link.
if (NeedsLink)
NeedsLink->Link = SplitNode;
NeedsLink = SplitNode;
}
// We've added something new to the tree, so there's one less suffix to
// add.
SuffixesToAdd--;
if (Active.Node->isRoot()) {
if (Active.Len > 0) {
Active.Len--;
Active.Idx = EndIdx - SuffixesToAdd + 1;
}
} else {
// Start the next phase at the next smallest suffix.
Active.Node = Active.Node->Link;
}
}
return SuffixesToAdd;
}
public:
/// Find all repeated substrings that satisfy \p BenefitFn.
///
/// If a substring appears at least twice, then it must be represented by
/// an internal node which appears in at least two suffixes. Each suffix is
/// represented by a leaf node. To do this, we visit each internal node in
/// the tree, using the leaf children of each internal node. If an internal
/// node represents a beneficial substring, then we use each of its leaf
/// children to find the locations of its substring.
///
/// \param[out] CandidateList Filled with candidates representing each
/// beneficial substring.
/// \param[out] FunctionList Filled with a list of \p OutlinedFunctions each
/// type of candidate.
/// \param BenefitFn The function to satisfy.
///
/// \returns The length of the longest candidate found.
size_t findCandidates(std::vector<Candidate> &CandidateList,
std::vector<OutlinedFunction> &FunctionList,
const std::function<unsigned(SuffixTreeNode &, size_t, unsigned)>
&BenefitFn) {
CandidateList.clear();
FunctionList.clear();
size_t FnIdx = 0;
size_t MaxLen = 0;
for (SuffixTreeNode* Leaf : LeafVector) {
assert(Leaf && "Leaves in LeafVector cannot be null!");
if (!Leaf->IsInTree)
continue;
assert(Leaf->Parent && "All leaves must have parents!");
SuffixTreeNode &Parent = *(Leaf->Parent);
// If it doesn't appear enough, or we already outlined from it, skip it.
if (Parent.OccurrenceCount < 2 || Parent.isRoot() || !Parent.IsInTree)
continue;
size_t StringLen = Leaf->ConcatLen - Leaf->size();
// How many instructions would outlining this string save?
unsigned Benefit = BenefitFn(Parent,
StringLen, Str[Leaf->SuffixIdx + StringLen - 1]);
// If it's not beneficial, skip it.
if (Benefit < 1)
continue;
if (StringLen > MaxLen)
MaxLen = StringLen;
unsigned OccurrenceCount = 0;
for (auto &ChildPair : Parent.Children) {
SuffixTreeNode *M = ChildPair.second;
// Is it a leaf? If so, we have an occurrence of this candidate.
if (M && M->IsInTree && M->isLeaf()) {
OccurrenceCount++;
CandidateList.emplace_back(M->SuffixIdx, StringLen, FnIdx);
CandidateList.back().Benefit = Benefit;
M->IsInTree = false;
}
}
// Save the function for the new candidate sequence.
std::vector<unsigned> CandidateSequence;
for (unsigned i = Leaf->SuffixIdx; i < Leaf->SuffixIdx + StringLen; i++)
CandidateSequence.push_back(Str[i]);
FunctionList.emplace_back(FnIdx, OccurrenceCount, CandidateSequence,
Benefit, false);
// Move to the next function.
FnIdx++;
Parent.IsInTree = false;
}
return MaxLen;
}
/// Construct a suffix tree from a sequence of unsigned integers.
///
/// \param Str The string to construct the suffix tree for.
SuffixTree(const std::vector<unsigned> &Str) : Str(Str) {
Root = insertInternalNode(nullptr, EmptyIdx, EmptyIdx, 0);
Root->IsInTree = true;
Active.Node = Root;
LeafVector = std::vector<SuffixTreeNode*>(Str.size());
// Keep track of the number of suffixes we have to add of the current
// prefix.
size_t SuffixesToAdd = 0;
Active.Node = Root;
// Construct the suffix tree iteratively on each prefix of the string.
// PfxEndIdx is the end index of the current prefix.
// End is one past the last element in the string.
for (size_t PfxEndIdx = 0, End = Str.size(); PfxEndIdx < End; PfxEndIdx++) {
SuffixesToAdd++;
LeafEndIdx = PfxEndIdx; // Extend each of the leaves.
SuffixesToAdd = extend(PfxEndIdx, SuffixesToAdd);
}
// Set the suffix indices of each leaf.
assert(Root && "Root node can't be nullptr!");
setSuffixIndices(*Root, 0);
}
};
/// \brief Maps \p MachineInstrs to unsigned integers and stores the mappings.
struct InstructionMapper {
/// \brief The next available integer to assign to a \p MachineInstr that
/// cannot be outlined.
///
/// Set to -3 for compatability with \p DenseMapInfo<unsigned>.
unsigned IllegalInstrNumber = -3;
/// \brief The next available integer to assign to a \p MachineInstr that can
/// be outlined.
unsigned LegalInstrNumber = 0;
/// Correspondence from \p MachineInstrs to unsigned integers.
DenseMap<MachineInstr *, unsigned, MachineInstrExpressionTrait>
InstructionIntegerMap;
/// Corresponcence from unsigned integers to \p MachineInstrs.
/// Inverse of \p InstructionIntegerMap.
DenseMap<unsigned, MachineInstr *> IntegerInstructionMap;
/// The vector of unsigned integers that the module is mapped to.
std::vector<unsigned> UnsignedVec;
/// \brief Stores the location of the instruction associated with the integer
/// at index i in \p UnsignedVec for each index i.
std::vector<MachineBasicBlock::iterator> InstrList;
/// \brief Maps \p *It to a legal integer.
///
/// Updates \p InstrList, \p UnsignedVec, \p InstructionIntegerMap,
/// \p IntegerInstructionMap, and \p LegalInstrNumber.
///
/// \returns The integer that \p *It was mapped to.
unsigned mapToLegalUnsigned(MachineBasicBlock::iterator &It) {
// Get the integer for this instruction or give it the current
// LegalInstrNumber.
InstrList.push_back(It);
MachineInstr &MI = *It;
bool WasInserted;
DenseMap<MachineInstr *, unsigned, MachineInstrExpressionTrait>::iterator
ResultIt;
std::tie(ResultIt, WasInserted) =
InstructionIntegerMap.insert(std::make_pair(&MI, LegalInstrNumber));
unsigned MINumber = ResultIt->second;
// There was an insertion.
if (WasInserted) {
LegalInstrNumber++;
IntegerInstructionMap.insert(std::make_pair(MINumber, &MI));
}
UnsignedVec.push_back(MINumber);
// Make sure we don't overflow or use any integers reserved by the DenseMap.
if (LegalInstrNumber >= IllegalInstrNumber)
report_fatal_error("Instruction mapping overflow!");
assert(LegalInstrNumber != DenseMapInfo<unsigned>::getEmptyKey()
&& "Tried to assign DenseMap tombstone or empty key to instruction.");
assert(LegalInstrNumber != DenseMapInfo<unsigned>::getTombstoneKey()
&& "Tried to assign DenseMap tombstone or empty key to instruction.");
return MINumber;
}
/// Maps \p *It to an illegal integer.
///
/// Updates \p InstrList, \p UnsignedVec, and \p IllegalInstrNumber.
///
/// \returns The integer that \p *It was mapped to.
unsigned mapToIllegalUnsigned(MachineBasicBlock::iterator &It) {
unsigned MINumber = IllegalInstrNumber;
InstrList.push_back(It);
UnsignedVec.push_back(IllegalInstrNumber);
IllegalInstrNumber--;
assert(LegalInstrNumber < IllegalInstrNumber &&
"Instruction mapping overflow!");
assert(IllegalInstrNumber !=
DenseMapInfo<unsigned>::getEmptyKey() &&
"IllegalInstrNumber cannot be DenseMap tombstone or empty key!");
assert(IllegalInstrNumber !=
DenseMapInfo<unsigned>::getTombstoneKey() &&
"IllegalInstrNumber cannot be DenseMap tombstone or empty key!");
return MINumber;
}
/// \brief Transforms a \p MachineBasicBlock into a \p vector of \p unsigneds
/// and appends it to \p UnsignedVec and \p InstrList.
///
/// Two instructions are assigned the same integer if they are identical.
/// If an instruction is deemed unsafe to outline, then it will be assigned an
/// unique integer. The resulting mapping is placed into a suffix tree and
/// queried for candidates.
///
/// \param MBB The \p MachineBasicBlock to be translated into integers.
/// \param TRI \p TargetRegisterInfo for the module.
/// \param TII \p TargetInstrInfo for the module.
void convertToUnsignedVec(MachineBasicBlock &MBB,
const TargetRegisterInfo &TRI,
const TargetInstrInfo &TII) {
for (MachineBasicBlock::iterator It = MBB.begin(), Et = MBB.end(); It != Et;
It++) {
// Keep track of where this instruction is in the module.
switch(TII.getOutliningType(*It)) {
case TargetInstrInfo::MachineOutlinerInstrType::Illegal:
mapToIllegalUnsigned(It);
break;
case TargetInstrInfo::MachineOutlinerInstrType::Legal:
mapToLegalUnsigned(It);
break;
case TargetInstrInfo::MachineOutlinerInstrType::Invisible:
break;
}
}
// After we're done every insertion, uniquely terminate this part of the
// "string". This makes sure we won't match across basic block or function
// boundaries since the "end" is encoded uniquely and thus appears in no
// repeated substring.
InstrList.push_back(MBB.end());
UnsignedVec.push_back(IllegalInstrNumber);
IllegalInstrNumber--;
}
InstructionMapper() {
// Make sure that the implementation of DenseMapInfo<unsigned> hasn't
// changed.
assert(DenseMapInfo<unsigned>::getEmptyKey() == (unsigned)-1 &&
"DenseMapInfo<unsigned>'s empty key isn't -1!");
assert(DenseMapInfo<unsigned>::getTombstoneKey() == (unsigned)-2 &&
"DenseMapInfo<unsigned>'s tombstone key isn't -2!");
}
};
/// \brief An interprocedural pass which finds repeated sequences of
/// instructions and replaces them with calls to functions.
///
/// Each instruction is mapped to an unsigned integer and placed in a string.
/// The resulting mapping is then placed in a \p SuffixTree. The \p SuffixTree
/// is then repeatedly queried for repeated sequences of instructions. Each
/// non-overlapping repeated sequence is then placed in its own
/// \p MachineFunction and each instance is then replaced with a call to that
/// function.
struct MachineOutliner : public ModulePass {
static char ID;
StringRef getPassName() const override { return "Machine Outliner"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineModuleInfo>();
AU.addPreserved<MachineModuleInfo>();
AU.setPreservesAll();
ModulePass::getAnalysisUsage(AU);
}
MachineOutliner() : ModulePass(ID) {
initializeMachineOutlinerPass(*PassRegistry::getPassRegistry());
}
/// \brief Replace the sequences of instructions represented by the
/// \p Candidates in \p CandidateList with calls to \p MachineFunctions
/// described in \p FunctionList.
///
/// \param M The module we are outlining from.
/// \param CandidateList A list of candidates to be outlined.
/// \param FunctionList A list of functions to be inserted into the module.
/// \param Mapper Contains the instruction mappings for the module.
bool outline(Module &M, const ArrayRef<Candidate> &CandidateList,
std::vector<OutlinedFunction> &FunctionList,
InstructionMapper &Mapper);
/// Creates a function for \p OF and inserts it into the module.
MachineFunction *createOutlinedFunction(Module &M, const OutlinedFunction &OF,
InstructionMapper &Mapper);
/// Find potential outlining candidates and store them in \p CandidateList.
///
/// For each type of potential candidate, also build an \p OutlinedFunction
/// struct containing the information to build the function for that
/// candidate.
///
/// \param[out] CandidateList Filled with outlining candidates for the module.
/// \param[out] FunctionList Filled with functions corresponding to each type
/// of \p Candidate.
/// \param ST The suffix tree for the module.
/// \param TII TargetInstrInfo for the module.
///
/// \returns The length of the longest candidate found. 0 if there are none.
unsigned buildCandidateList(std::vector<Candidate> &CandidateList,
std::vector<OutlinedFunction> &FunctionList,
SuffixTree &ST,
InstructionMapper &Mapper,
const TargetInstrInfo &TII);
/// \brief Remove any overlapping candidates that weren't handled by the
/// suffix tree's pruning method.
///
/// Pruning from the suffix tree doesn't necessarily remove all overlaps.
/// If a short candidate is chosen for outlining, then a longer candidate
/// which has that short candidate as a suffix is chosen, the tree's pruning
/// method will not find it. Thus, we need to prune before outlining as well.
///
/// \param[in,out] CandidateList A list of outlining candidates.
/// \param[in,out] FunctionList A list of functions to be outlined.
/// \param MaxCandidateLen The length of the longest candidate.
/// \param TII TargetInstrInfo for the module.
void pruneOverlaps(std::vector<Candidate> &CandidateList,
std::vector<OutlinedFunction> &FunctionList,
unsigned MaxCandidateLen,
const TargetInstrInfo &TII);
/// Construct a suffix tree on the instructions in \p M and outline repeated
/// strings from that tree.
bool runOnModule(Module &M) override;
};
} // Anonymous namespace.
char MachineOutliner::ID = 0;
namespace llvm {
ModulePass *createMachineOutlinerPass() { return new MachineOutliner(); }
}
INITIALIZE_PASS(MachineOutliner, "machine-outliner",
"Machine Function Outliner", false, false)
void MachineOutliner::pruneOverlaps(std::vector<Candidate> &CandidateList,
std::vector<OutlinedFunction> &FunctionList,
unsigned MaxCandidateLen,
const TargetInstrInfo &TII) {
// TODO: Experiment with interval trees or other interval-checking structures
// to lower the time complexity of this function.
// TODO: Can we do better than the simple greedy choice?
// Check for overlaps in the range.
// This is O(MaxCandidateLen * CandidateList.size()).
for (auto It = CandidateList.begin(), Et = CandidateList.end(); It != Et;
It++) {
Candidate &C1 = *It;
OutlinedFunction &F1 = FunctionList[C1.FunctionIdx];
// If we removed this candidate, skip it.
if (!C1.InCandidateList)
continue;
// Is it still worth it to outline C1?
if (F1.Benefit < 1 || F1.OccurrenceCount < 2) {
assert(F1.OccurrenceCount > 0 &&
"Can't remove OutlinedFunction with no occurrences!");
F1.OccurrenceCount--;
C1.InCandidateList = false;
continue;
}
// The minimum start index of any candidate that could overlap with this
// one.
unsigned FarthestPossibleIdx = 0;
// Either the index is 0, or it's at most MaxCandidateLen indices away.
if (C1.StartIdx > MaxCandidateLen)
FarthestPossibleIdx = C1.StartIdx - MaxCandidateLen;
// Compare against the candidates in the list that start at at most
// FarthestPossibleIdx indices away from C1. There are at most
// MaxCandidateLen of these.
for (auto Sit = It + 1; Sit != Et; Sit++) {
Candidate &C2 = *Sit;
OutlinedFunction &F2 = FunctionList[C2.FunctionIdx];
// Is this candidate too far away to overlap?
if (C2.StartIdx < FarthestPossibleIdx)
break;
// Did we already remove this candidate in a previous step?
if (!C2.InCandidateList)
continue;
// Is the function beneficial to outline?
if (F2.OccurrenceCount < 2 || F2.Benefit < 1) {
// If not, remove this candidate and move to the next one.
assert(F2.OccurrenceCount > 0 &&
"Can't remove OutlinedFunction with no occurrences!");
F2.OccurrenceCount--;
C2.InCandidateList = false;
continue;
}
size_t C2End = C2.StartIdx + C2.Len - 1;
// Do C1 and C2 overlap?
//
// Not overlapping:
// High indices... [C1End ... C1Start][C2End ... C2Start] ...Low indices
//
// We sorted our candidate list so C2Start <= C1Start. We know that
// C2End > C2Start since each candidate has length >= 2. Therefore, all we
// have to check is C2End < C2Start to see if we overlap.
if (C2End < C1.StartIdx)
continue;
// C1 and C2 overlap.
// We need to choose the better of the two.
//
// Approximate this by picking the one which would have saved us the
// most instructions before any pruning.
if (C1.Benefit >= C2.Benefit) {
// C1 is better, so remove C2 and update C2's OutlinedFunction to
// reflect the removal.
assert(F2.OccurrenceCount > 0 &&
"Can't remove OutlinedFunction with no occurrences!");
F2.OccurrenceCount--;
F2.Benefit = TII.getOutliningBenefit(F2.Sequence.size(),
F2.OccurrenceCount,
F2.IsTailCall
);
C2.InCandidateList = false;
DEBUG (
dbgs() << "- Removed C2. \n";
dbgs() << "--- Num fns left for C2: " << F2.OccurrenceCount << "\n";
dbgs() << "--- C2's benefit: " << F2.Benefit << "\n";
);
} else {
// C2 is better, so remove C1 and update C1's OutlinedFunction to
// reflect the removal.
assert(F1.OccurrenceCount > 0 &&
"Can't remove OutlinedFunction with no occurrences!");
F1.OccurrenceCount--;
F1.Benefit = TII.getOutliningBenefit(F1.Sequence.size(),
F1.OccurrenceCount,
F1.IsTailCall
);
C1.InCandidateList = false;
DEBUG (
dbgs() << "- Removed C1. \n";
dbgs() << "--- Num fns left for C1: " << F1.OccurrenceCount << "\n";
dbgs() << "--- C1's benefit: " << F1.Benefit << "\n";
);
// C1 is out, so we don't have to compare it against anyone else.
break;
}
}
}
}
unsigned
MachineOutliner::buildCandidateList(std::vector<Candidate> &CandidateList,
std::vector<OutlinedFunction> &FunctionList,
SuffixTree &ST,
InstructionMapper &Mapper,
const TargetInstrInfo &TII) {
std::vector<unsigned> CandidateSequence; // Current outlining candidate.
size_t MaxCandidateLen = 0; // Length of the longest candidate.
// Function for maximizing query in the suffix tree.
// This allows us to define more fine-grained types of things to outline in
// the target without putting target-specific info in the suffix tree.
auto BenefitFn = [&TII, &Mapper](const SuffixTreeNode &Curr,
size_t StringLen, unsigned EndVal) {
// The root represents the empty string.
if (Curr.isRoot())
return 0u;
// Is this long enough to outline?
// TODO: Let the target decide how "long" a string is in terms of the sizes
// of the instructions in the string. For example, if a call instruction
// is smaller than a one instruction string, we should outline that string.
if (StringLen < 2)
return 0u;
size_t Occurrences = Curr.OccurrenceCount;
// Anything we want to outline has to appear at least twice.
if (Occurrences < 2)
return 0u;
// Check if the last instruction in the sequence is a return.
MachineInstr *LastInstr =
Mapper.IntegerInstructionMap[EndVal];
assert(LastInstr && "Last instruction in sequence was unmapped!");
// The only way a terminator could be mapped as legal is if it was safe to
// tail call.
bool IsTailCall = LastInstr->isTerminator();
return TII.getOutliningBenefit(StringLen, Occurrences, IsTailCall);
};
MaxCandidateLen = ST.findCandidates(CandidateList, FunctionList, BenefitFn);
for (auto &OF : FunctionList)
OF.IsTailCall = Mapper.
IntegerInstructionMap[OF.Sequence.back()]->isTerminator();
// Sort the candidates in decending order. This will simplify the outlining
// process when we have to remove the candidates from the mapping by
// allowing us to cut them out without keeping track of an offset.
std::stable_sort(CandidateList.begin(), CandidateList.end());
return MaxCandidateLen;
}
MachineFunction *
MachineOutliner::createOutlinedFunction(Module &M, const OutlinedFunction &OF,
InstructionMapper &Mapper) {
// Create the function name. This should be unique. For now, just hash the
// module name and include it in the function name plus the number of this
// function.
std::ostringstream NameStream;
NameStream << "OUTLINED_FUNCTION" << "_" << OF.Name;
// Create the function using an IR-level function.
LLVMContext &C = M.getContext();
Function *F = dyn_cast<Function>(
M.getOrInsertFunction(NameStream.str(), Type::getVoidTy(C)));
assert(F && "Function was null!");
// NOTE: If this is linkonceodr, then we can take advantage of linker deduping
// which gives us better results when we outline from linkonceodr functions.
F->setLinkage(GlobalValue::PrivateLinkage);
F->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
BasicBlock *EntryBB = BasicBlock::Create(C, "entry", F);
IRBuilder<> Builder(EntryBB);
Builder.CreateRetVoid();
MachineModuleInfo &MMI = getAnalysis<MachineModuleInfo>();
MachineFunction &MF = MMI.getMachineFunction(*F);
MachineBasicBlock &MBB = *MF.CreateMachineBasicBlock();
const TargetSubtargetInfo &STI = MF.getSubtarget();
const TargetInstrInfo &TII = *STI.getInstrInfo();
// Insert the new function into the module.
MF.insert(MF.begin(), &MBB);
TII.insertOutlinerPrologue(MBB, MF, OF.IsTailCall);
// Copy over the instructions for the function using the integer mappings in
// its sequence.
for (unsigned Str : OF.Sequence) {
MachineInstr *NewMI =
MF.CloneMachineInstr(Mapper.IntegerInstructionMap.find(Str)->second);
NewMI->dropMemRefs();
// Don't keep debug information for outlined instructions.
// FIXME: This means outlined functions are currently undebuggable.
NewMI->setDebugLoc(DebugLoc());
MBB.insert(MBB.end(), NewMI);
}
TII.insertOutlinerEpilogue(MBB, MF, OF.IsTailCall);
return &MF;
}
bool MachineOutliner::outline(Module &M,
const ArrayRef<Candidate> &CandidateList,
std::vector<OutlinedFunction> &FunctionList,
InstructionMapper &Mapper) {
bool OutlinedSomething = false;
// Replace the candidates with calls to their respective outlined functions.
for (const Candidate &C : CandidateList) {
// Was the candidate removed during pruneOverlaps?
if (!C.InCandidateList)
continue;
// If not, then look at its OutlinedFunction.
OutlinedFunction &OF = FunctionList[C.FunctionIdx];
// Was its OutlinedFunction made unbeneficial during pruneOverlaps?
if (OF.OccurrenceCount < 2 || OF.Benefit < 1)
continue;
// If not, then outline it.
assert(C.StartIdx < Mapper.InstrList.size() && "Candidate out of bounds!");
MachineBasicBlock *MBB = (*Mapper.InstrList[C.StartIdx]).getParent();
MachineBasicBlock::iterator StartIt = Mapper.InstrList[C.StartIdx];
unsigned EndIdx = C.StartIdx + C.Len - 1;
assert(EndIdx < Mapper.InstrList.size() && "Candidate out of bounds!");
MachineBasicBlock::iterator EndIt = Mapper.InstrList[EndIdx];
assert(EndIt != MBB->end() && "EndIt out of bounds!");
EndIt++; // Erase needs one past the end index.
// Does this candidate have a function yet?
if (!OF.MF) {
OF.MF = createOutlinedFunction(M, OF, Mapper);
FunctionsCreated++;
}
MachineFunction *MF = OF.MF;
const TargetSubtargetInfo &STI = MF->getSubtarget();
const TargetInstrInfo &TII = *STI.getInstrInfo();
// Insert a call to the new function and erase the old sequence.
TII.insertOutlinedCall(M, *MBB, StartIt, *MF, OF.IsTailCall);
StartIt = Mapper.InstrList[C.StartIdx];
MBB->erase(StartIt, EndIt);
OutlinedSomething = true;
// Statistics.
NumOutlined++;
}
DEBUG (
dbgs() << "OutlinedSomething = " << OutlinedSomething << "\n";
);
return OutlinedSomething;
}
bool MachineOutliner::runOnModule(Module &M) {
// Is there anything in the module at all?
if (M.empty())
return false;
MachineModuleInfo &MMI = getAnalysis<MachineModuleInfo>();
const TargetSubtargetInfo &STI = MMI.getMachineFunction(*M.begin())
.getSubtarget();
const TargetRegisterInfo *TRI = STI.getRegisterInfo();
const TargetInstrInfo *TII = STI.getInstrInfo();
InstructionMapper Mapper;
// Build instruction mappings for each function in the module.
for (Function &F : M) {
MachineFunction &MF = MMI.getMachineFunction(F);
// Is the function empty? Safe to outline from?
if (F.empty() || !TII->isFunctionSafeToOutlineFrom(MF))
continue;
// If it is, look at each MachineBasicBlock in the function.
for (MachineBasicBlock &MBB : MF) {
// Is there anything in MBB?
if (MBB.empty())
continue;
// If yes, map it.
Mapper.convertToUnsignedVec(MBB, *TRI, *TII);
}
}
// Construct a suffix tree, use it to find candidates, and then outline them.
SuffixTree ST(Mapper.UnsignedVec);
std::vector<Candidate> CandidateList;
std::vector<OutlinedFunction> FunctionList;
// Find all of the outlining candidates.
unsigned MaxCandidateLen =
buildCandidateList(CandidateList, FunctionList, ST, Mapper, *TII);
// Remove candidates that overlap with other candidates.
pruneOverlaps(CandidateList, FunctionList, MaxCandidateLen, *TII);
// Outline each of the candidates and return true if something was outlined.
return outline(M, CandidateList, FunctionList, Mapper);
}
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