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Move IDF Calculation to a separate file, expose an interface to it. 

Summary:
MemorySSA uses this algorithm as well, and this enables us to reuse the code in both places.

There are no actual algorithm or datastructure changes in here, just code movement.

Reviewers: qcolombet, chandlerc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9118

llvm-svn: 235406
This commit is contained in:
Daniel Berlin 2015-04-21 19:13:02 +00:00
parent 0d7c6942a1
commit 2372a193ba
4 changed files with 224 additions and 130 deletions
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96
llvm/include/llvm/Analysis/IteratedDominanceFrontier.h Normal file
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@ -0,0 +1,96 @@
//===- IteratedDominanceFrontier.h - Calculate IDF --------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \brief Compute iterated dominance frontiers using a linear time algorithm.
///
/// The algorithm used here is based on:
///
/// Sreedhar and Gao. A linear time algorithm for placing phi-nodes.
/// In Proceedings of the 22nd ACM SIGPLAN-SIGACT Symposium on Principles of
/// Programming Languages
/// POPL '95. ACM, New York, NY, 62-73.
///
/// It has been modified to not explicitly use the DJ graph data structure and
/// to directly compute pruned SSA using per-variable liveness information.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_IDF_H
#define LLVM_ANALYSIS_IDF_H
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
namespace llvm {
class BasicBlock;
template <class T> class DomTreeNodeBase;
typedef DomTreeNodeBase<BasicBlock> DomTreeNode;
class DominatorTree;
/// \brief Determine the iterated dominance frontier, given a set of defining
/// blocks, and optionally, a set of live-in blocks.
///
/// In turn, the results can be used to place phi nodes.
///
/// This algorithm is a linear time computation of Iterated Dominance Frontiers,
/// pruned using the live-in set.
/// By default, liveness is not used to prune the IDF computation.
class IDFCalculator {
public:
IDFCalculator(DominatorTree &DT) : DT(DT), useLiveIn(false) {}
/// \brief Give the IDF calculator the set of blocks in which the value is
/// defined. This is equivalent to the set of starting blocks it should be
/// calculating the IDF for (though later gets pruned based on liveness).
///
/// Note: This set *must* live for the entire lifetime of the IDF calculator.
void setDefiningBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
DefBlocks = &Blocks;
}
/// \brief Give the IDF calculator the set of blocks in which the value is
/// live on entry to the block. This is used to prune the IDF calculation to
/// not include blocks where any phi insertion would be dead.
///
/// Note: This set *must* live for the entire lifetime of the IDF calculator.
void setLiveInBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
LiveInBlocks = &Blocks;
useLiveIn = true;
}
/// \brief Reset the live-in block set to be empty, and tell the IDF
/// calculator to not use liveness anymore.
void resetLiveInBlocks() {
LiveInBlocks = nullptr;
useLiveIn = false;
}
/// \brief Calculate iterated dominance frontiers
///
/// This uses the linear-time phi algorithm based on DJ-graphs mentioned in
/// the file-level comment. It performs DF->IDF pruning using the live-in
/// set, to avoid computing the IDF for blocks where an inserted PHI node
/// would be dead.
void calculate(SmallVectorImpl<BasicBlock *> &IDFBlocks);
private:
DominatorTree &DT;
bool useLiveIn;
DenseMap<DomTreeNode *, unsigned> DomLevels;
const SmallPtrSetImpl<BasicBlock *> *LiveInBlocks;
const SmallPtrSetImpl<BasicBlock *> *DefBlocks;
SmallVector<BasicBlock *, 32> PHIBlocks;
};
}
#endif

1
llvm/lib/Analysis/CMakeLists.txt
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@ -28,6 +28,7 @@ add_llvm_library(LLVMAnalysis
InstructionSimplify.cpp
Interval.cpp
IntervalPartition.cpp
IteratedDominanceFrontier.cpp
LazyCallGraph.cpp
LazyValueInfo.cpp
LibCallAliasAnalysis.cpp

95
llvm/lib/Analysis/IteratedDominanceFrontier.cpp Normal file
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@ -0,0 +1,95 @@
//===- IteratedDominanceFrontier.cpp - Compute IDF ------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \brief Compute iterated dominance frontiers using a linear time algorithm.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/IteratedDominanceFrontier.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Dominators.h"
#include <queue>
using namespace llvm;
void IDFCalculator::calculate(SmallVectorImpl<BasicBlock *> &PHIBlocks) {
// If we haven't computed dominator tree levels, do so now.
if (DomLevels.empty()) {
for (auto DFI = df_begin(DT.getRootNode()), DFE = df_end(DT.getRootNode());
DFI != DFE; ++DFI) {
DomLevels[*DFI] = DFI.getPathLength() - 1;
}
}
// Use a priority queue keyed on dominator tree level so that inserted nodes
// are handled from the bottom of the dominator tree upwards.
typedef std::pair<DomTreeNode *, unsigned> DomTreeNodePair;
typedef std::priority_queue<DomTreeNodePair, SmallVector<DomTreeNodePair, 32>,
less_second> IDFPriorityQueue;
IDFPriorityQueue PQ;
for (BasicBlock *BB : *DefBlocks) {
if (DomTreeNode *Node = DT.getNode(BB))
PQ.push(std::make_pair(Node, DomLevels.lookup(Node)));
}
SmallVector<DomTreeNode *, 32> Worklist;
SmallPtrSet<DomTreeNode *, 32> VisitedPQ;
SmallPtrSet<DomTreeNode *, 32> VisitedWorklist;
while (!PQ.empty()) {
DomTreeNodePair RootPair = PQ.top();
PQ.pop();
DomTreeNode *Root = RootPair.first;
unsigned RootLevel = RootPair.second;
// Walk all dominator tree children of Root, inspecting their CFG edges with
// targets elsewhere on the dominator tree. Only targets whose level is at
// most Root's level are added to the iterated dominance frontier of the
// definition set.
Worklist.clear();
Worklist.push_back(Root);
VisitedWorklist.insert(Root);
while (!Worklist.empty()) {
DomTreeNode *Node = Worklist.pop_back_val();
BasicBlock *BB = Node->getBlock();
for (auto Succ : successors(BB)) {
DomTreeNode *SuccNode = DT.getNode(Succ);
// Quickly skip all CFG edges that are also dominator tree edges instead
// of catching them below.
if (SuccNode->getIDom() == Node)
continue;
unsigned SuccLevel = DomLevels.lookup(SuccNode);
if (SuccLevel > RootLevel)
continue;
if (!VisitedPQ.insert(SuccNode).second)
continue;
BasicBlock *SuccBB = SuccNode->getBlock();
if (useLiveIn && !LiveInBlocks->count(SuccBB))
continue;
PHIBlocks.emplace_back(SuccBB);
if (!DefBlocks->count(SuccBB))
PQ.push(std::make_pair(SuccNode, SuccLevel));
}
for (auto DomChild : *Node) {
if (VisitedWorklist.insert(DomChild).second)
Worklist.push_back(DomChild);
}
}
}
}

162
llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
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@ -13,16 +13,6 @@
// traversing the function in depth-first order to rewrite loads and stores as
// appropriate.
//
// The algorithm used here is based on:
//
// Sreedhar and Gao. A linear time algorithm for placing phi-nodes.
// In Proceedings of the 22nd ACM SIGPLAN-SIGACT Symposium on Principles of
// Programming Languages
// POPL '95. ACM, New York, NY, 62-73.
//
// It has been modified to not explicitly use the DJ graph data structure and to
// directly compute pruned SSA using per-variable liveness information.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
@ -34,6 +24,7 @@
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasSetTracker.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/IteratedDominanceFrontier.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
@ -48,7 +39,6 @@
#include "llvm/IR/Module.h"
#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
#include <queue>
using namespace llvm;
#define DEBUG_TYPE "mem2reg"
@ -275,9 +265,6 @@ struct PromoteMem2Reg {
/// behavior.
DenseMap<BasicBlock *, unsigned> BBNumbers;
/// Maps DomTreeNodes to their level in the dominator tree.
DenseMap<DomTreeNode *, unsigned> DomLevels;
/// Lazily compute the number of predecessors a block has.
DenseMap<const BasicBlock *, unsigned> BBNumPreds;
@ -304,8 +291,6 @@ private:
return NP - 1;
}
void DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum,
AllocaInfo &Info);
void ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info,
const SmallPtrSetImpl<BasicBlock *> &DefBlocks,
SmallPtrSetImpl<BasicBlock *> &LiveInBlocks);
@ -532,6 +517,7 @@ void PromoteMem2Reg::run() {
AllocaInfo Info;
LargeBlockInfo LBI;
IDFCalculator IDF(DT);
for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
AllocaInst *AI = Allocas[AllocaNum];
@ -579,31 +565,12 @@ void PromoteMem2Reg::run() {
continue;
}
// If we haven't computed dominator tree levels, do so now.
if (DomLevels.empty()) {
SmallVector<DomTreeNode *, 32> Worklist;
DomTreeNode *Root = DT.getRootNode();
DomLevels[Root] = 0;
Worklist.push_back(Root);
while (!Worklist.empty()) {
DomTreeNode *Node = Worklist.pop_back_val();
unsigned ChildLevel = DomLevels[Node] + 1;
for (DomTreeNode::iterator CI = Node->begin(), CE = Node->end();
CI != CE; ++CI) {
DomLevels[*CI] = ChildLevel;
Worklist.push_back(*CI);
}
}
}
// If we haven't computed a numbering for the BB's in the function, do so
// now.
if (BBNumbers.empty()) {
unsigned ID = 0;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
BBNumbers[I] = ID++;
for (auto &BB : F)
BBNumbers[&BB] = ID++;
}
// If we have an AST to keep updated, remember some pointer value that is
@ -622,7 +589,34 @@ void PromoteMem2Reg::run() {
// the standard SSA construction algorithm. Determine which blocks need PHI
// nodes and see if we can optimize out some work by avoiding insertion of
// dead phi nodes.
DetermineInsertionPoint(AI, AllocaNum, Info);
// Unique the set of defining blocks for efficient lookup.
SmallPtrSet<BasicBlock *, 32> DefBlocks;
DefBlocks.insert(Info.DefiningBlocks.begin(), Info.DefiningBlocks.end());
// Determine which blocks the value is live in. These are blocks which lead
// to uses.
SmallPtrSet<BasicBlock *, 32> LiveInBlocks;
ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks);
// At this point, we're committed to promoting the alloca using IDF's, and
// the standard SSA construction algorithm. Determine which blocks need phi
// nodes and see if we can optimize out some work by avoiding insertion of
// dead phi nodes.
IDF.setLiveInBlocks(LiveInBlocks);
IDF.setDefiningBlocks(DefBlocks);
SmallVector<BasicBlock *, 32> PHIBlocks;
IDF.calculate(PHIBlocks);
if (PHIBlocks.size() > 1)
std::sort(PHIBlocks.begin(), PHIBlocks.end(),
[this](BasicBlock *A, BasicBlock *B) {
return BBNumbers.lookup(A) < BBNumbers.lookup(B);
});
unsigned CurrentVersion = 0;
for (unsigned i = 0, e = PHIBlocks.size(); i != e; ++i)
QueuePhiNode(PHIBlocks[i], AllocaNum, CurrentVersion);
}
if (Allocas.empty())
@ -844,98 +838,6 @@ void PromoteMem2Reg::ComputeLiveInBlocks(
}
}
/// At this point, we're committed to promoting the alloca using IDF's, and the
/// standard SSA construction algorithm. Determine which blocks need phi nodes
/// and see if we can optimize out some work by avoiding insertion of dead phi
/// nodes.
void PromoteMem2Reg::DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum,
AllocaInfo &Info) {
// Unique the set of defining blocks for efficient lookup.
SmallPtrSet<BasicBlock *, 32> DefBlocks;
DefBlocks.insert(Info.DefiningBlocks.begin(), Info.DefiningBlocks.end());
// Determine which blocks the value is live in. These are blocks which lead
// to uses.
SmallPtrSet<BasicBlock *, 32> LiveInBlocks;
ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks);
// Use a priority queue keyed on dominator tree level so that inserted nodes
// are handled from the bottom of the dominator tree upwards.
typedef std::pair<DomTreeNode *, unsigned> DomTreeNodePair;
typedef std::priority_queue<DomTreeNodePair, SmallVector<DomTreeNodePair, 32>,
less_second> IDFPriorityQueue;
IDFPriorityQueue PQ;
for (BasicBlock *BB : DefBlocks) {
if (DomTreeNode *Node = DT.getNode(BB))
PQ.push(std::make_pair(Node, DomLevels[Node]));
}
SmallVector<std::pair<unsigned, BasicBlock *>, 32> DFBlocks;
SmallVector<DomTreeNode *, 32> Worklist;
SmallPtrSet<DomTreeNode *, 32> VisitedPQ;
SmallPtrSet<DomTreeNode *, 32> VisitedWorklist;
while (!PQ.empty()) {
DomTreeNodePair RootPair = PQ.top();
PQ.pop();
DomTreeNode *Root = RootPair.first;
unsigned RootLevel = RootPair.second;
// Walk all dominator tree children of Root, inspecting their CFG edges with
// targets elsewhere on the dominator tree. Only targets whose level is at
// most Root's level are added to the iterated dominance frontier of the
// definition set.
Worklist.clear();
Worklist.push_back(Root);
VisitedWorklist.insert(Root);
while (!Worklist.empty()) {
DomTreeNode *Node = Worklist.pop_back_val();
BasicBlock *BB = Node->getBlock();
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
++SI) {
DomTreeNode *SuccNode = DT.getNode(*SI);
// Quickly skip all CFG edges that are also dominator tree edges instead
// of catching them below.
if (SuccNode->getIDom() == Node)
continue;
unsigned SuccLevel = DomLevels[SuccNode];
if (SuccLevel > RootLevel)
continue;
if (!VisitedPQ.insert(SuccNode).second)
continue;
BasicBlock *SuccBB = SuccNode->getBlock();
if (!LiveInBlocks.count(SuccBB))
continue;
DFBlocks.push_back(std::make_pair(BBNumbers[SuccBB], SuccBB));
if (!DefBlocks.count(SuccBB))
PQ.push(std::make_pair(SuccNode, SuccLevel));
}
for (DomTreeNode::iterator CI = Node->begin(), CE = Node->end(); CI != CE;
++CI) {
if (VisitedWorklist.insert(*CI).second)
Worklist.push_back(*CI);
}
}
}
if (DFBlocks.size() > 1)
std::sort(DFBlocks.begin(), DFBlocks.end());
unsigned CurrentVersion = 0;
for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i)
QueuePhiNode(DFBlocks[i].second, AllocaNum, CurrentVersion);
}
/// \brief Queue a phi-node to be added to a basic-block for a specific Alloca.
///
/// Returns true if there wasn't already a phi-node for that variable