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Combine the implementations of the core part of the SSAUpdater and

Browse Source 
MachineSSAUpdater to avoid duplicating all the code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103060 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bob Wilson 2010-05-04 23:18:19 +00:00
parent d2760d1cba
commit 4aad88d1fd
5 changed files with 707 additions and 927 deletions
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18
include/llvm/CodeGen/MachineSSAUpdater.h
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@ -23,6 +23,7 @@ namespace llvm {
class TargetInstrInfo;
class TargetRegisterClass;
template<typename T> class SmallVectorImpl;
template<typename T> class SSAUpdaterTraits;
class BumpPtrAllocator;
/// MachineSSAUpdater - This class updates SSA form for a set of virtual
@ -30,9 +31,7 @@ namespace llvm {
/// or another unstructured transformation wants to rewrite a set of uses of one
/// vreg with uses of a set of vregs.
class MachineSSAUpdater {
public:
class BBInfo;
typedef SmallVectorImpl<BBInfo*> BlockListTy;
friend class SSAUpdaterTraits<MachineSSAUpdater>;
private:
/// AvailableVals - This keeps track of which value to use on a per-block
@ -40,11 +39,6 @@ private:
//typedef DenseMap<MachineBasicBlock*, unsigned > AvailableValsTy;
void *AV;
/// BBMap - The GetValueAtEndOfBlock method maintains this mapping from
/// basic blocks to BBInfo structures.
/// typedef DenseMap<MachineBasicBlock*, BBInfo*> BBMapTy;
void *BM;
/// VR - Current virtual register whose uses are being updated.
unsigned VR;
@ -111,14 +105,6 @@ public:
private:
void ReplaceRegWith(unsigned OldReg, unsigned NewReg);
unsigned GetValueAtEndOfBlockInternal(MachineBasicBlock *BB);
void BuildBlockList(MachineBasicBlock *BB, BlockListTy *BlockList,
BumpPtrAllocator *Allocator);
void FindDominators(BlockListTy *BlockList);
void FindPHIPlacement(BlockListTy *BlockList);
void FindAvailableVals(BlockListTy *BlockList);
void FindExistingPHI(MachineBasicBlock *BB, BlockListTy *BlockList);
bool CheckIfPHIMatches(MachineInstr *PHI);
void RecordMatchingPHI(MachineInstr *PHI);
void operator=(const MachineSSAUpdater&); // DO NOT IMPLEMENT
MachineSSAUpdater(const MachineSSAUpdater&); // DO NOT IMPLEMENT

22
include/llvm/Transforms/Utils/SSAUpdater.h
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@ -19,8 +19,8 @@ namespace llvm {
class BasicBlock;
class Use;
class PHINode;
template<typename T>
class SmallVectorImpl;
template<typename T> class SmallVectorImpl;
template<typename T> class SSAUpdaterTraits;
class BumpPtrAllocator;
/// SSAUpdater - This class updates SSA form for a set of values defined in
@ -28,9 +28,7 @@ namespace llvm {
/// transformation wants to rewrite a set of uses of one value with uses of a
/// set of values.
class SSAUpdater {
public:
class BBInfo;
typedef SmallVectorImpl<BBInfo*> BlockListTy;
friend class SSAUpdaterTraits<SSAUpdater>;
private:
/// AvailableVals - This keeps track of which value to use on a per-block
@ -42,14 +40,10 @@ private:
/// and a type for PHI nodes.
Value *PrototypeValue;
/// BBMap - The GetValueAtEndOfBlock method maintains this mapping from
/// basic blocks to BBInfo structures.
/// typedef DenseMap<BasicBlock*, BBInfo*> BBMapTy;
void *BM;
/// InsertedPHIs - If this is non-null, the SSAUpdater adds all PHI nodes that
/// it creates to the vector.
SmallVectorImpl<PHINode*> *InsertedPHIs;
public:
/// SSAUpdater constructor. If InsertedPHIs is specified, it will be filled
/// in with all PHI Nodes created by rewriting.
@ -102,14 +96,6 @@ public:
private:
Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
void BuildBlockList(BasicBlock *BB, BlockListTy *BlockList,
BumpPtrAllocator *Allocator);
void FindDominators(BlockListTy *BlockList);
void FindPHIPlacement(BlockListTy *BlockList);
void FindAvailableVals(BlockListTy *BlockList);
void FindExistingPHI(BasicBlock *BB, BlockListTy *BlockList);
bool CheckIfPHIMatches(PHINode *PHI);
void RecordMatchingPHI(PHINode *PHI);
void operator=(const SSAUpdater&); // DO NOT IMPLEMENT
SSAUpdater(const SSAUpdater&); // DO NOT IMPLEMENT

463
include/llvm/Transforms/Utils/SSAUpdaterImpl.h Normal file
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@ -0,0 +1,463 @@
//===-- SSAUpdaterImpl.h - SSA Updater Implementation -----------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file provides a template that implements the core algorithm for the
// SSAUpdater and MachineSSAUpdater.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_UTILS_SSAUPDATERIMPL_H
#define LLVM_TRANSFORMS_UTILS_SSAUPDATERIMPL_H
namespace llvm {
template<typename T> class SSAUpdaterTraits;
template<typename UpdaterT>
class SSAUpdaterImpl {
private:
UpdaterT *Updater;
typedef SSAUpdaterTraits<UpdaterT> Traits;
typedef typename Traits::BlkT BlkT;
typedef typename Traits::ValT ValT;
typedef typename Traits::PhiT PhiT;
/// BBInfo - Per-basic block information used internally by SSAUpdaterImpl.
/// The predecessors of each block are cached here since pred_iterator is
/// slow and we need to iterate over the blocks at least a few times.
class BBInfo {
public:
BlkT *BB; // Back-pointer to the corresponding block.
ValT AvailableVal; // Value to use in this block.
BBInfo *DefBB; // Block that defines the available value.
int BlkNum; // Postorder number.
BBInfo *IDom; // Immediate dominator.
unsigned NumPreds; // Number of predecessor blocks.
BBInfo **Preds; // Array[NumPreds] of predecessor blocks.
PhiT *PHITag; // Marker for existing PHIs that match.
BBInfo(BlkT *ThisBB, ValT V)
: BB(ThisBB), AvailableVal(V), DefBB(V ? this : 0), BlkNum(0), IDom(0),
NumPreds(0), Preds(0), PHITag(0) { }
};
typedef DenseMap<BlkT*, ValT> AvailableValsTy;
AvailableValsTy *AvailableVals;
SmallVectorImpl<PhiT*> *InsertedPHIs;
typedef SmallVectorImpl<BBInfo*> BlockListTy;
typedef DenseMap<BlkT*, BBInfo*> BBMapTy;
BBMapTy BBMap;
BumpPtrAllocator Allocator;
public:
explicit SSAUpdaterImpl(UpdaterT *U, AvailableValsTy *A,
SmallVectorImpl<PhiT*> *Ins) :
Updater(U), AvailableVals(A), InsertedPHIs(Ins) { }
/// GetValue - Check to see if AvailableVals has an entry for the specified
/// BB and if so, return it. If not, construct SSA form by first
/// calculating the required placement of PHIs and then inserting new PHIs
/// where needed.
ValT GetValue(BlkT *BB) {
SmallVector<BBInfo*, 100> BlockList;
BuildBlockList(BB, &BlockList);
// Special case: bail out if BB is unreachable.
if (BlockList.size() == 0) {
ValT V = Traits::GetUndefVal(BB, Updater);
(*AvailableVals)[BB] = V;
return V;
}
FindDominators(&BlockList);
FindPHIPlacement(&BlockList);
FindAvailableVals(&BlockList);
return BBMap[BB]->DefBB->AvailableVal;
}
/// BuildBlockList - Starting from the specified basic block, traverse back
/// through its predecessors until reaching blocks with known values.
/// Create BBInfo structures for the blocks and append them to the block
/// list.
void BuildBlockList(BlkT *BB, BlockListTy *BlockList) {
SmallVector<BBInfo*, 10> RootList;
SmallVector<BBInfo*, 64> WorkList;
BBInfo *Info = new (Allocator) BBInfo(BB, 0);
BBMap[BB] = Info;
WorkList.push_back(Info);
// Search backward from BB, creating BBInfos along the way and stopping
// when reaching blocks that define the value. Record those defining
// blocks on the RootList.
SmallVector<BlkT*, 10> Preds;
while (!WorkList.empty()) {
Info = WorkList.pop_back_val();
Preds.clear();
Traits::FindPredecessorBlocks(Info->BB, &Preds);
Info->NumPreds = Preds.size();
Info->Preds = static_cast<BBInfo**>
(Allocator.Allocate(Info->NumPreds * sizeof(BBInfo*),
AlignOf<BBInfo*>::Alignment));
// Treat an unreachable predecessor as a definition with 'undef'.
if (Info->NumPreds == 0) {
Info->AvailableVal = Traits::GetUndefVal(Info->BB, Updater);
Info->DefBB = Info;
RootList.push_back(Info);
continue;
}
for (unsigned p = 0; p != Info->NumPreds; ++p) {
BlkT *Pred = Preds[p];
// Check if BBMap already has a BBInfo for the predecessor block.
typename BBMapTy::value_type &BBMapBucket =
BBMap.FindAndConstruct(Pred);
if (BBMapBucket.second) {
Info->Preds[p] = BBMapBucket.second;
continue;
}
// Create a new BBInfo for the predecessor.
ValT PredVal = AvailableVals->lookup(Pred);
BBInfo *PredInfo = new (Allocator) BBInfo(Pred, PredVal);
BBMapBucket.second = PredInfo;
Info->Preds[p] = PredInfo;
if (PredInfo->AvailableVal) {
RootList.push_back(PredInfo);
continue;
}
WorkList.push_back(PredInfo);
}
}
// Now that we know what blocks are backwards-reachable from the starting
// block, do a forward depth-first traversal to assign postorder numbers
// to those blocks.
BBInfo *PseudoEntry = new (Allocator) BBInfo(0, 0);
unsigned BlkNum = 1;
// Initialize the worklist with the roots from the backward traversal.
while (!RootList.empty()) {
Info = RootList.pop_back_val();
Info->IDom = PseudoEntry;
Info->BlkNum = -1;
WorkList.push_back(Info);
}
while (!WorkList.empty()) {
Info = WorkList.back();
if (Info->BlkNum == -2) {
// All the successors have been handled; assign the postorder number.
Info->BlkNum = BlkNum++;
// If not a root, put it on the BlockList.
if (!Info->AvailableVal)
BlockList->push_back(Info);
WorkList.pop_back();
continue;
}
// Leave this entry on the worklist, but set its BlkNum to mark that its
// successors have been put on the worklist. When it returns to the top
// the list, after handling its successors, it will be assigned a
// number.
Info->BlkNum = -2;
// Add unvisited successors to the work list.
for (typename Traits::BlkSucc_iterator SI =
Traits::BlkSucc_begin(Info->BB),
E = Traits::BlkSucc_end(Info->BB); SI != E; ++SI) {
BBInfo *SuccInfo = BBMap[*SI];
if (!SuccInfo || SuccInfo->BlkNum)
continue;
SuccInfo->BlkNum = -1;
WorkList.push_back(SuccInfo);
}
}
PseudoEntry->BlkNum = BlkNum;
}
/// IntersectDominators - This is the dataflow lattice "meet" operation for
/// finding dominators. Given two basic blocks, it walks up the dominator
/// tree until it finds a common dominator of both. It uses the postorder
/// number of the blocks to determine how to do that.
BBInfo *IntersectDominators(BBInfo *Blk1, BBInfo *Blk2) {
while (Blk1 != Blk2) {
while (Blk1->BlkNum < Blk2->BlkNum) {
Blk1 = Blk1->IDom;
if (!Blk1)
return Blk2;
}
while (Blk2->BlkNum < Blk1->BlkNum) {
Blk2 = Blk2->IDom;
if (!Blk2)
return Blk1;
}
}
return Blk1;
}
/// FindDominators - Calculate the dominator tree for the subset of the CFG
/// corresponding to the basic blocks on the BlockList. This uses the
/// algorithm from: "A Simple, Fast Dominance Algorithm" by Cooper, Harvey
/// and Kennedy, published in Software--Practice and Experience, 2001,
/// 4:1-10. Because the CFG subset does not include any edges leading into
/// blocks that define the value, the results are not the usual dominator
/// tree. The CFG subset has a single pseudo-entry node with edges to a set
/// of root nodes for blocks that define the value. The dominators for this
/// subset CFG are not the standard dominators but they are adequate for
/// placing PHIs within the subset CFG.
void FindDominators(BlockListTy *BlockList) {
bool Changed;
do {
Changed = false;
// Iterate over the list in reverse order, i.e., forward on CFG edges.
for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
E = BlockList->rend(); I != E; ++I) {
BBInfo *Info = *I;
// Start with the first predecessor.
assert(Info->NumPreds > 0 && "unreachable block");
BBInfo *NewIDom = Info->Preds[0];
// Iterate through the block's other predecessors.
for (unsigned p = 1; p != Info->NumPreds; ++p) {
BBInfo *Pred = Info->Preds[p];
NewIDom = IntersectDominators(NewIDom, Pred);
}
// Check if the IDom value has changed.
if (NewIDom != Info->IDom) {
Info->IDom = NewIDom;
Changed = true;
}
}
} while (Changed);
}
/// IsDefInDomFrontier - Search up the dominator tree from Pred to IDom for
/// any blocks containing definitions of the value. If one is found, then
/// the successor of Pred is in the dominance frontier for the definition,
/// and this function returns true.
bool IsDefInDomFrontier(const BBInfo *Pred, const BBInfo *IDom) {
for (; Pred != IDom; Pred = Pred->IDom) {
if (Pred->DefBB == Pred)
return true;
}
return false;
}
/// FindPHIPlacement - PHIs are needed in the iterated dominance frontiers
/// of the known definitions. Iteratively add PHIs in the dom frontiers
/// until nothing changes. Along the way, keep track of the nearest
/// dominating definitions for non-PHI blocks.
void FindPHIPlacement(BlockListTy *BlockList) {
bool Changed;
do {
Changed = false;
// Iterate over the list in reverse order, i.e., forward on CFG edges.
for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
E = BlockList->rend(); I != E; ++I) {
BBInfo *Info = *I;
// If this block already needs a PHI, there is nothing to do here.
if (Info->DefBB == Info)
continue;
// Default to use the same def as the immediate dominator.
BBInfo *NewDefBB = Info->IDom->DefBB;
for (unsigned p = 0; p != Info->NumPreds; ++p) {
if (IsDefInDomFrontier(Info->Preds[p], Info->IDom)) {
// Need a PHI here.
NewDefBB = Info;
break;
}
}
// Check if anything changed.
if (NewDefBB != Info->DefBB) {
Info->DefBB = NewDefBB;
Changed = true;
}
}
} while (Changed);
}
/// FindAvailableVal - If this block requires a PHI, first check if an
/// existing PHI matches the PHI placement and reaching definitions computed
/// earlier, and if not, create a new PHI. Visit all the block's
/// predecessors to calculate the available value for each one and fill in
/// the incoming values for a new PHI.
void FindAvailableVals(BlockListTy *BlockList) {
// Go through the worklist in forward order (i.e., backward through the CFG)
// and check if existing PHIs can be used. If not, create empty PHIs where
// they are needed.
for (typename BlockListTy::iterator I = BlockList->begin(),
E = BlockList->end(); I != E; ++I) {
BBInfo *Info = *I;
// Check if there needs to be a PHI in BB.
if (Info->DefBB != Info)
continue;
// Look for an existing PHI.
FindExistingPHI(Info->BB, BlockList);
if (Info->AvailableVal)
continue;
ValT PHI = Traits::CreateEmptyPHI(Info->BB, Info->NumPreds, Updater);
Info->AvailableVal = PHI;
(*AvailableVals)[Info->BB] = PHI;
}
// Now go back through the worklist in reverse order to fill in the
// arguments for any new PHIs added in the forward traversal.
for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
E = BlockList->rend(); I != E; ++I) {
BBInfo *Info = *I;
if (Info->DefBB != Info) {
// Record the available value at join nodes to speed up subsequent
// uses of this SSAUpdater for the same value.
if (Info->NumPreds > 1)
(*AvailableVals)[Info->BB] = Info->DefBB->AvailableVal;
continue;
}
// Check if this block contains a newly added PHI.
PhiT *PHI = Traits::ValueIsNewPHI(Info->AvailableVal, Updater);
if (!PHI)
continue;
// Iterate through the block's predecessors.
for (unsigned p = 0; p != Info->NumPreds; ++p) {
BBInfo *PredInfo = Info->Preds[p];
BlkT *Pred = PredInfo->BB;
// Skip to the nearest preceding definition.
if (PredInfo->DefBB != PredInfo)
PredInfo = PredInfo->DefBB;
Traits::AddPHIOperand(PHI, PredInfo->AvailableVal, Pred);
}
DEBUG(dbgs() << " Inserted PHI: " << *PHI << "\n");
// If the client wants to know about all new instructions, tell it.
if (InsertedPHIs) InsertedPHIs->push_back(PHI);
}
}
/// FindExistingPHI - Look through the PHI nodes in a block to see if any of
/// them match what is needed.
void FindExistingPHI(BlkT *BB, BlockListTy *BlockList) {
for (typename BlkT::iterator BBI = BB->begin(), BBE = BB->end();
BBI != BBE; ++BBI) {
PhiT *SomePHI = Traits::InstrIsPHI(BBI);
if (!SomePHI)
break;
if (CheckIfPHIMatches(SomePHI)) {
RecordMatchingPHI(SomePHI);
break;
}
// Match failed: clear all the PHITag values.
for (typename BlockListTy::iterator I = BlockList->begin(),
E = BlockList->end(); I != E; ++I)
(*I)->PHITag = 0;
}
}
/// CheckIfPHIMatches - Check if a PHI node matches the placement and values
/// in the BBMap.
bool CheckIfPHIMatches(PhiT *PHI) {
SmallVector<PhiT*, 20> WorkList;
WorkList.push_back(PHI);
// Mark that the block containing this PHI has been visited.
BBMap[PHI->getParent()]->PHITag = PHI;
while (!WorkList.empty()) {
PHI = WorkList.pop_back_val();
// Iterate through the PHI's incoming values.
for (typename Traits::PHI_iterator I = Traits::PHI_begin(PHI),
E = Traits::PHI_end(PHI); I != E; ++I) {
ValT IncomingVal = I.getIncomingValue();
BBInfo *PredInfo = BBMap[I.getIncomingBlock()];
// Skip to the nearest preceding definition.
if (PredInfo->DefBB != PredInfo)
PredInfo = PredInfo->DefBB;
// Check if it matches the expected value.
if (PredInfo->AvailableVal) {
if (IncomingVal == PredInfo->AvailableVal)
continue;
return false;
}
// Check if the value is a PHI in the correct block.
PhiT *IncomingPHIVal = Traits::ValueIsPHI(IncomingVal, Updater);
if (!IncomingPHIVal || IncomingPHIVal->getParent() != PredInfo->BB)
return false;
// If this block has already been visited, check if this PHI matches.
if (PredInfo->PHITag) {
if (IncomingPHIVal == PredInfo->PHITag)
continue;
return false;
}
PredInfo->PHITag = IncomingPHIVal;
WorkList.push_back(IncomingPHIVal);
}
}
return true;
}
/// RecordMatchingPHI - For a PHI node that matches, record it and its input
/// PHIs in both the BBMap and the AvailableVals mapping.
void RecordMatchingPHI(PhiT *PHI) {
SmallVector<PhiT*, 20> WorkList;
WorkList.push_back(PHI);
// Record this PHI.
BlkT *BB = PHI->getParent();
ValT PHIVal = Traits::GetPHIValue(PHI);
(*AvailableVals)[BB] = PHIVal;
BBMap[BB]->AvailableVal = PHIVal;
while (!WorkList.empty()) {
PHI = WorkList.pop_back_val();
// Iterate through the PHI's incoming values.
for (typename Traits::PHI_iterator I = Traits::PHI_begin(PHI),
E = Traits::PHI_end(PHI); I != E; ++I) {
ValT IncomingVal = I.getIncomingValue();
PhiT *IncomingPHI = Traits::ValueIsPHI(IncomingVal, Updater);
if (!IncomingPHI) continue;
BB = IncomingPHI->getParent();
BBInfo *Info = BBMap[BB];
if (!Info || Info->AvailableVal)
continue;
// Record the PHI and add it to the worklist.
(*AvailableVals)[BB] = IncomingVal;
Info->AvailableVal = IncomingVal;
WorkList.push_back(IncomingPHI);
}
}
}
};
} // End llvm namespace
#endif

572
lib/CodeGen/MachineSSAUpdater.cpp
View File

@ -26,39 +26,17 @@
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
using namespace llvm;
/// BBInfo - Per-basic block information used internally by MachineSSAUpdater.
class MachineSSAUpdater::BBInfo {
public:
MachineBasicBlock *BB; // Back-pointer to the corresponding block.
unsigned AvailableVal; // Value to use in this block.
BBInfo *DefBB; // Block that defines the available value.
int BlkNum; // Postorder number.
BBInfo *IDom; // Immediate dominator.
unsigned NumPreds; // Number of predecessor blocks.
BBInfo **Preds; // Array[NumPreds] of predecessor blocks.
MachineInstr *PHITag; // Marker for existing PHIs that match.
BBInfo(MachineBasicBlock *ThisBB, unsigned V)
: BB(ThisBB), AvailableVal(V), DefBB(V ? this : 0), BlkNum(0), IDom(0),
NumPreds(0), Preds(0), PHITag(0) { }
};
typedef DenseMap<MachineBasicBlock*, MachineSSAUpdater::BBInfo*> BBMapTy;
typedef DenseMap<MachineBasicBlock*, unsigned> AvailableValsTy;
static AvailableValsTy &getAvailableVals(void *AV) {
return *static_cast<AvailableValsTy*>(AV);
}
static BBMapTy *getBBMap(void *BM) {
return static_cast<BBMapTy*>(BM);
}
MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
SmallVectorImpl<MachineInstr*> *NewPHI)
: AV(0), BM(0), InsertedPHIs(NewPHI) {
: AV(0), InsertedPHIs(NewPHI) {
TII = MF.getTarget().getInstrInfo();
MRI = &MF.getRegInfo();
}
@ -134,7 +112,8 @@ static
MachineInstr *InsertNewDef(unsigned Opcode,
MachineBasicBlock *BB, MachineBasicBlock::iterator I,
const TargetRegisterClass *RC,
MachineRegisterInfo *MRI, const TargetInstrInfo *TII) {
MachineRegisterInfo *MRI,
const TargetInstrInfo *TII) {
unsigned NewVR = MRI->createVirtualRegister(RC);
return BuildMI(*BB, I, DebugLoc(), TII->get(Opcode), NewVR);
}
@ -263,6 +242,122 @@ void MachineSSAUpdater::ReplaceRegWith(unsigned OldReg, unsigned NewReg) {
I->second = NewReg;
}
/// MachinePHIiter - Iterator for PHI operands. This is used for the
/// PHI_iterator in the SSAUpdaterImpl template.
namespace {
class MachinePHIiter {
private:
MachineInstr *PHI;
unsigned idx;
public:
explicit MachinePHIiter(MachineInstr *P) // begin iterator
: PHI(P), idx(1) {}
MachinePHIiter(MachineInstr *P, bool) // end iterator
: PHI(P), idx(PHI->getNumOperands()) {}
MachinePHIiter &operator++() { idx += 2; return *this; }
bool operator==(const MachinePHIiter& x) const { return idx == x.idx; }
bool operator!=(const MachinePHIiter& x) const { return !operator==(x); }
unsigned getIncomingValue() { return PHI->getOperand(idx).getReg(); }
MachineBasicBlock *getIncomingBlock() {
return PHI->getOperand(idx+1).getMBB();
}
};
}
/// SSAUpdaterTraits<MachineSSAUpdater> - Traits for the SSAUpdaterImpl
/// template, specialized for MachineSSAUpdater.
namespace llvm {
template<>
class SSAUpdaterTraits<MachineSSAUpdater> {
public:
typedef MachineBasicBlock BlkT;
typedef unsigned ValT;
typedef MachineInstr PhiT;
typedef MachineBasicBlock::succ_iterator BlkSucc_iterator;
static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return BB->succ_begin(); }
static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return BB->succ_end(); }
typedef MachinePHIiter PHI_iterator;
static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
static inline PHI_iterator PHI_end(PhiT *PHI) {
return PHI_iterator(PHI, true);
}
/// FindPredecessorBlocks - Put the predecessors of BB into the Preds
/// vector.
static void FindPredecessorBlocks(MachineBasicBlock *BB,
SmallVectorImpl<MachineBasicBlock*> *Preds){
for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
E = BB->pred_end(); PI != E; ++PI)
Preds->push_back(*PI);
}
/// GetUndefVal - Create an IMPLICIT_DEF instruction with a new register.
/// Add it into the specified block and return the register.
static unsigned GetUndefVal(MachineBasicBlock *BB,
MachineSSAUpdater *Updater) {
// Insert an implicit_def to represent an undef value.
MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
BB, BB->getFirstTerminator(),
Updater->VRC, Updater->MRI,
Updater->TII);
return NewDef->getOperand(0).getReg();
}
/// CreateEmptyPHI - Create a PHI instruction that defines a new register.
/// Add it into the specified block and return the register.
static unsigned CreateEmptyPHI(MachineBasicBlock *BB, unsigned NumPreds,
MachineSSAUpdater *Updater) {
MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->front();
MachineInstr *PHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
Updater->VRC, Updater->MRI,
Updater->TII);
return PHI->getOperand(0).getReg();
}
/// AddPHIOperand - Add the specified value as an operand of the PHI for
/// the specified predecessor block.
static void AddPHIOperand(MachineInstr *PHI, unsigned Val,
MachineBasicBlock *Pred) {
PHI->addOperand(MachineOperand::CreateReg(Val, false));
PHI->addOperand(MachineOperand::CreateMBB(Pred));
}
/// InstrIsPHI - Check if an instruction is a PHI.
///
static MachineInstr *InstrIsPHI(MachineInstr *I) {
if (I->isPHI())
return I;
return 0;
}
/// ValueIsPHI - Check if the instruction that defines the specified register
/// is a PHI instruction.
static MachineInstr *ValueIsPHI(unsigned Val, MachineSSAUpdater *Updater) {
return InstrIsPHI(Updater->MRI->getVRegDef(Val));
}
/// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
/// operands, i.e., it was just added.
static MachineInstr *ValueIsNewPHI(unsigned Val, MachineSSAUpdater *Updater) {
MachineInstr *PHI = ValueIsPHI(Val, Updater);
if (PHI && PHI->getNumOperands() <= 1)
return PHI;
return 0;
}
/// GetPHIValue - For the specified PHI instruction, return the register
/// that it defines.
static unsigned GetPHIValue(MachineInstr *PHI) {
return PHI->getOperand(0).getReg();
}
};
} // End llvm namespace
/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
/// for the specified BB and if so, return it. If not, construct SSA form by
/// first calculating the required placement of PHIs and then inserting new
@ -272,429 +367,6 @@ unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
if (unsigned V = AvailableVals[BB])
return V;
// Pool allocation used internally by GetValueAtEndOfBlock.
BumpPtrAllocator Allocator;
BBMapTy BBMapObj;
BM = &BBMapObj;
SmallVector<BBInfo*, 100> BlockList;
BuildBlockList(BB, &BlockList, &Allocator);
// Special case: bail out if BB is unreachable.
if (BlockList.size() == 0) {
BM = 0;
// Insert an implicit_def to represent an undef value.
MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
BB, BB->getFirstTerminator(),
VRC, MRI, TII);
unsigned V = NewDef->getOperand(0).getReg();
AvailableVals[BB] = V;
return V;
}
FindDominators(&BlockList);
FindPHIPlacement(&BlockList);
FindAvailableVals(&BlockList);
BM = 0;
return BBMapObj[BB]->DefBB->AvailableVal;
}
/// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
/// vector, set Info->NumPreds, and allocate space in Info->Preds.
static void FindPredecessorBlocks(MachineSSAUpdater::BBInfo *Info,
SmallVectorImpl<MachineBasicBlock*> *Preds,
BumpPtrAllocator *Allocator) {
MachineBasicBlock *BB = Info->BB;
for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
E = BB->pred_end(); PI != E; ++PI)
Preds->push_back(*PI);
Info->NumPreds = Preds->size();
Info->Preds = static_cast<MachineSSAUpdater::BBInfo**>
(Allocator->Allocate(Info->NumPreds * sizeof(MachineSSAUpdater::BBInfo*),
AlignOf<MachineSSAUpdater::BBInfo*>::Alignment));
}
/// BuildBlockList - Starting from the specified basic block, traverse back
/// through its predecessors until reaching blocks with known values. Create
/// BBInfo structures for the blocks and append them to the block list.
void MachineSSAUpdater::BuildBlockList(MachineBasicBlock *BB,
BlockListTy *BlockList,
BumpPtrAllocator *Allocator) {
AvailableValsTy &AvailableVals = getAvailableVals(AV);
BBMapTy *BBMap = getBBMap(BM);
SmallVector<BBInfo*, 10> RootList;
SmallVector<BBInfo*, 64> WorkList;
BBInfo *Info = new (*Allocator) BBInfo(BB, 0);
(*BBMap)[BB] = Info;
WorkList.push_back(Info);
// Search backward from BB, creating BBInfos along the way and stopping when
// reaching blocks that define the value. Record those defining blocks on
// the RootList.
SmallVector<MachineBasicBlock*, 10> Preds;
while (!WorkList.empty()) {
Info = WorkList.pop_back_val();
Preds.clear();
FindPredecessorBlocks(Info, &Preds, Allocator);
// Treat an unreachable predecessor as a definition with 'undef'.
if (Info->NumPreds == 0) {
// Insert an implicit_def to represent an undef value.
MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
Info->BB,
Info->BB->getFirstTerminator(),
VRC, MRI, TII);
Info->AvailableVal = NewDef->getOperand(0).getReg();
Info->DefBB = Info;
RootList.push_back(Info);
continue;
}
for (unsigned p = 0; p != Info->NumPreds; ++p) {
MachineBasicBlock *Pred = Preds[p];
// Check if BBMap already has a BBInfo for the predecessor block.
BBMapTy::value_type &BBMapBucket = BBMap->FindAndConstruct(Pred);
if (BBMapBucket.second) {
Info->Preds[p] = BBMapBucket.second;
continue;
}
// Create a new BBInfo for the predecessor.
unsigned PredVal = AvailableVals.lookup(Pred);
BBInfo *PredInfo = new (*Allocator) BBInfo(Pred, PredVal);
BBMapBucket.second = PredInfo;
Info->Preds[p] = PredInfo;
if (PredInfo->AvailableVal) {
RootList.push_back(PredInfo);
continue;
}
WorkList.push_back(PredInfo);
}
}
// Now that we know what blocks are backwards-reachable from the starting
// block, do a forward depth-first traversal to assign postorder numbers
// to those blocks.
BBInfo *PseudoEntry = new (*Allocator) BBInfo(0, 0);
unsigned BlkNum = 1;
// Initialize the worklist with the roots from the backward traversal.
while (!RootList.empty()) {
Info = RootList.pop_back_val();
Info->IDom = PseudoEntry;
Info->BlkNum = -1;
WorkList.push_back(Info);
}
while (!WorkList.empty()) {
Info = WorkList.back();
if (Info->BlkNum == -2) {
// All the successors have been handled; assign the postorder number.
Info->BlkNum = BlkNum++;
// If not a root, put it on the BlockList.
if (!Info->AvailableVal)
BlockList->push_back(Info);
WorkList.pop_back();
continue;
}
// Leave this entry on the worklist, but set its BlkNum to mark that its
// successors have been put on the worklist. When it returns to the top
// the list, after handling its successors, it will be assigned a number.
Info->BlkNum = -2;
// Add unvisited successors to the work list.
for (MachineBasicBlock::succ_iterator SI = Info->BB->succ_begin(),
E = Info->BB->succ_end(); SI != E; ++SI) {
BBInfo *SuccInfo = (*BBMap)[*SI];
if (!SuccInfo || SuccInfo->BlkNum)
continue;
SuccInfo->BlkNum = -1;
WorkList.push_back(SuccInfo);
}
}
PseudoEntry->BlkNum = BlkNum;
}
/// IntersectDominators - This is the dataflow lattice "meet" operation for
/// finding dominators. Given two basic blocks, it walks up the dominator
/// tree until it finds a common dominator of both. It uses the postorder
/// number of the blocks to determine how to do that.
static MachineSSAUpdater::BBInfo *
IntersectDominators(MachineSSAUpdater::BBInfo *Blk1,
MachineSSAUpdater::BBInfo *Blk2) {
while (Blk1 != Blk2) {
while (Blk1->BlkNum < Blk2->BlkNum) {
Blk1 = Blk1->IDom;
if (!Blk1)
return Blk2;
}
while (Blk2->BlkNum < Blk1->BlkNum) {
Blk2 = Blk2->IDom;
if (!Blk2)
return Blk1;
}
}
return Blk1;
}
/// FindDominators - Calculate the dominator tree for the subset of the CFG
/// corresponding to the basic blocks on the BlockList. This uses the
/// algorithm from: "A Simple, Fast Dominance Algorithm" by Cooper, Harvey and
/// Kennedy, published in Software--Practice and Experience, 2001, 4:1-10.
/// Because the CFG subset does not include any edges leading into blocks that
/// define the value, the results are not the usual dominator tree. The CFG
/// subset has a single pseudo-entry node with edges to a set of root nodes
/// for blocks that define the value. The dominators for this subset CFG are
/// not the standard dominators but they are adequate for placing PHIs within
/// the subset CFG.
void MachineSSAUpdater::FindDominators(BlockListTy *BlockList) {
bool Changed;
do {
Changed = false;
// Iterate over the list in reverse order, i.e., forward on CFG edges.
for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
E = BlockList->rend(); I != E; ++I) {
BBInfo *Info = *I;
// Start with the first predecessor.
assert(Info->NumPreds > 0 && "unreachable block");
BBInfo *NewIDom = Info->Preds[0];
// Iterate through the block's other predecessors.
for (unsigned p = 1; p != Info->NumPreds; ++p) {
BBInfo *Pred = Info->Preds[p];
NewIDom = IntersectDominators(NewIDom, Pred);
}
// Check if the IDom value has changed.
if (NewIDom != Info->IDom) {
Info->IDom = NewIDom;
Changed = true;
}
}
} while (Changed);
}
/// IsDefInDomFrontier - Search up the dominator tree from Pred to IDom for
/// any blocks containing definitions of the value. If one is found, then the
/// successor of Pred is in the dominance frontier for the definition, and
/// this function returns true.
static bool IsDefInDomFrontier(const MachineSSAUpdater::BBInfo *Pred,
const MachineSSAUpdater::BBInfo *IDom) {
for (; Pred != IDom; Pred = Pred->IDom) {
if (Pred->DefBB == Pred)
return true;
}
return false;
}
/// FindPHIPlacement - PHIs are needed in the iterated dominance frontiers of
/// the known definitions. Iteratively add PHIs in the dom frontiers until
/// nothing changes. Along the way, keep track of the nearest dominating
/// definitions for non-PHI blocks.
void MachineSSAUpdater::FindPHIPlacement(BlockListTy *BlockList) {
bool Changed;
do {
Changed = false;
// Iterate over the list in reverse order, i.e., forward on CFG edges.
for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
E = BlockList->rend(); I != E; ++I) {
BBInfo *Info = *I;
// If this block already needs a PHI, there is nothing to do here.
if (Info->DefBB == Info)
continue;
// Default to use the same def as the immediate dominator.
BBInfo *NewDefBB = Info->IDom->DefBB;
for (unsigned p = 0; p != Info->NumPreds; ++p) {
if (IsDefInDomFrontier(Info->Preds[p], Info->IDom)) {
// Need a PHI here.
NewDefBB = Info;
break;
}
}
// Check if anything changed.
if (NewDefBB != Info->DefBB) {
Info->DefBB = NewDefBB;
Changed = true;
}
}
} while (Changed);
}
/// FindAvailableVal - If this block requires a PHI, first check if an existing
/// PHI matches the PHI placement and reaching definitions computed earlier,
/// and if not, create a new PHI. Visit all the block's predecessors to
/// calculate the available value for each one and fill in the incoming values
/// for a new PHI.
void MachineSSAUpdater::FindAvailableVals(BlockListTy *BlockList) {
AvailableValsTy &AvailableVals = getAvailableVals(AV);
// Go through the worklist in forward order (i.e., backward through the CFG)
// and check if existing PHIs can be used. If not, create empty PHIs where
// they are needed.
for (BlockListTy::iterator I = BlockList->begin(), E = BlockList->end();
I != E; ++I) {
BBInfo *Info = *I;
// Check if there needs to be a PHI in BB.
if (Info->DefBB != Info)
continue;
// Look for an existing PHI.
FindExistingPHI(Info->BB, BlockList);
if (Info->AvailableVal)
continue;
MachineBasicBlock::iterator Loc =
Info->BB->empty() ? Info->BB->end() : Info->BB->front();
MachineInstr *InsertedPHI = InsertNewDef(TargetOpcode::PHI, Info->BB, Loc,
VRC, MRI, TII);
unsigned PHI = InsertedPHI->getOperand(0).getReg();
Info->AvailableVal = PHI;
AvailableVals[Info->BB] = PHI;
}
// Now go back through the worklist in reverse order to fill in the arguments
// for any new PHIs added in the forward traversal.
for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
E = BlockList->rend(); I != E; ++I) {
BBInfo *Info = *I;
if (Info->DefBB != Info) {
// Record the available value at join nodes to speed up subsequent
// uses of this SSAUpdater for the same value.
if (Info->NumPreds > 1)
AvailableVals[Info->BB] = Info->DefBB->AvailableVal;
continue;
}
// Check if this block contains a newly added PHI.
unsigned PHI = Info->AvailableVal;
MachineInstr *InsertedPHI = MRI->getVRegDef(PHI);
if (!InsertedPHI->isPHI() || InsertedPHI->getNumOperands() > 1)
continue;
// Iterate through the block's predecessors.
MachineInstrBuilder MIB(InsertedPHI);
for (unsigned p = 0; p != Info->NumPreds; ++p) {
BBInfo *PredInfo = Info->Preds[p];
MachineBasicBlock *Pred = PredInfo->BB;
// Skip to the nearest preceding definition.
if (PredInfo->DefBB != PredInfo)
PredInfo = PredInfo->DefBB;
MIB.addReg(PredInfo->AvailableVal).addMBB(Pred);
}
DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
// If the client wants to know about all new instructions, tell it.
if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
}
}
/// FindExistingPHI - Look through the PHI nodes in a block to see if any of
/// them match what is needed.
void MachineSSAUpdater::FindExistingPHI(MachineBasicBlock *BB,
BlockListTy *BlockList) {
for (MachineBasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
BBI != BBE && BBI->isPHI(); ++BBI) {
if (CheckIfPHIMatches(BBI)) {
RecordMatchingPHI(BBI);
break;
}
// Match failed: clear all the PHITag values.
for (BlockListTy::iterator I = BlockList->begin(), E = BlockList->end();
I != E; ++I)
(*I)->PHITag = 0;
}
}
/// CheckIfPHIMatches - Check if a PHI node matches the placement and values
/// in the BBMap.
bool MachineSSAUpdater::CheckIfPHIMatches(MachineInstr *PHI) {
BBMapTy *BBMap = getBBMap(BM);
SmallVector<MachineInstr*, 20> WorkList;
WorkList.push_back(PHI);
// Mark that the block containing this PHI has been visited.
(*BBMap)[PHI->getParent()]->PHITag = PHI;
while (!WorkList.empty()) {
PHI = WorkList.pop_back_val();
// Iterate through the PHI's incoming values.
for (unsigned i = 1, e = PHI->getNumOperands(); i != e; i += 2) {
unsigned IncomingVal = PHI->getOperand(i).getReg();
BBInfo *PredInfo = (*BBMap)[PHI->getOperand(i+1).getMBB()];
// Skip to the nearest preceding definition.
if (PredInfo->DefBB != PredInfo)
PredInfo = PredInfo->DefBB;
// Check if it matches the expected value.
if (PredInfo->AvailableVal) {
if (IncomingVal == PredInfo->AvailableVal)
continue;
return false;
}
// Check if the value is a PHI in the correct block.
MachineInstr *IncomingPHIVal = MRI->getVRegDef(IncomingVal);
if (!IncomingPHIVal->isPHI() ||
IncomingPHIVal->getParent() != PredInfo->BB)
return false;
// If this block has already been visited, check if this PHI matches.
if (PredInfo->PHITag) {
if (IncomingPHIVal == PredInfo->PHITag)
continue;
return false;
}
PredInfo->PHITag = IncomingPHIVal;
WorkList.push_back(IncomingPHIVal);
}
}
return true;
}
/// RecordMatchingPHI - For a PHI node that matches, record it and its input
/// PHIs in both the BBMap and the AvailableVals mapping.
void MachineSSAUpdater::RecordMatchingPHI(MachineInstr *PHI) {
BBMapTy *BBMap = getBBMap(BM);
AvailableValsTy &AvailableVals = getAvailableVals(AV);
SmallVector<MachineInstr*, 20> WorkList;
WorkList.push_back(PHI);
// Record this PHI.
MachineBasicBlock *BB = PHI->getParent();
AvailableVals[BB] = PHI->getOperand(0).getReg();
(*BBMap)[BB]->AvailableVal = PHI->getOperand(0).getReg();
while (!WorkList.empty()) {
PHI = WorkList.pop_back_val();
// Iterate through the PHI's incoming values.
for (unsigned i = 1, e = PHI->getNumOperands(); i != e; i += 2) {
unsigned IncomingVal = PHI->getOperand(i).getReg();
MachineInstr *IncomingPHIVal = MRI->getVRegDef(IncomingVal);
if (!IncomingPHIVal->isPHI()) continue;
BB = IncomingPHIVal->getParent();
BBInfo *Info = (*BBMap)[BB];
if (!Info || Info->AvailableVal)
continue;
// Record the PHI and add it to the worklist.
AvailableVals[BB] = IncomingVal;
Info->AvailableVal = IncomingVal;
WorkList.push_back(IncomingPHIVal);
}
}
SSAUpdaterImpl<MachineSSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
return Impl.GetValue(BB);
}

559
lib/Transforms/Utils/SSAUpdater.cpp
View File

@ -12,7 +12,6 @@
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ssaupdater"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Instructions.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/Support/AlignOf.h"
@ -20,40 +19,17 @@
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
using namespace llvm;
/// BBInfo - Per-basic block information used internally by SSAUpdater.
/// The predecessors of each block are cached here since pred_iterator is
/// slow and we need to iterate over the blocks at least a few times.
class SSAUpdater::BBInfo {
public:
BasicBlock *BB; // Back-pointer to the corresponding block.
Value *AvailableVal; // Value to use in this block.
BBInfo *DefBB; // Block that defines the available value.
int BlkNum; // Postorder number.
BBInfo *IDom; // Immediate dominator.
unsigned NumPreds; // Number of predecessor blocks.
BBInfo **Preds; // Array[NumPreds] of predecessor blocks.
PHINode *PHITag; // Marker for existing PHIs that match.
BBInfo(BasicBlock *ThisBB, Value *V)
: BB(ThisBB), AvailableVal(V), DefBB(V ? this : 0), BlkNum(0), IDom(0),
NumPreds(0), Preds(0), PHITag(0) { }
};
typedef DenseMap<BasicBlock*, SSAUpdater::BBInfo*> BBMapTy;
typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
static AvailableValsTy &getAvailableVals(void *AV) {
return *static_cast<AvailableValsTy*>(AV);
}
static BBMapTy *getBBMap(void *BM) {
return static_cast<BBMapTy*>(BM);
}
SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
: AV(0), PrototypeValue(0), BM(0), InsertedPHIs(NewPHI) {}
: AV(0), PrototypeValue(0), InsertedPHIs(NewPHI) {}
SSAUpdater::~SSAUpdater() {
delete &getAvailableVals(AV);
@ -105,9 +81,7 @@ static bool IsEquivalentPHI(PHINode *PHI,
/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
/// live at the end of the specified block.
Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
assert(BM == 0 && "Unexpected Internal State");
Value *Res = GetValueAtEndOfBlockInternal(BB);
assert(BM == 0 && "Unexpected Internal State");
return Res;
}
@ -231,6 +205,117 @@ void SSAUpdater::RewriteUse(Use &U) {
U.set(V);
}
/// PHIiter - Iterator for PHI operands. This is used for the PHI_iterator
/// in the SSAUpdaterImpl template.
namespace {
class PHIiter {
private:
PHINode *PHI;
unsigned idx;
public:
explicit PHIiter(PHINode *P) // begin iterator
: PHI(P), idx(0) {}
PHIiter(PHINode *P, bool) // end iterator
: PHI(P), idx(PHI->getNumIncomingValues()) {}
PHIiter &operator++() { ++idx; return *this; }
bool operator==(const PHIiter& x) const { return idx == x.idx; }
bool operator!=(const PHIiter& x) const { return !operator==(x); }
Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
};
}
/// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template,
/// specialized for SSAUpdater.
namespace llvm {
template<>
class SSAUpdaterTraits<SSAUpdater> {
public:
typedef BasicBlock BlkT;
typedef Value *ValT;
typedef PHINode PhiT;
typedef succ_iterator BlkSucc_iterator;
static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
typedef PHIiter PHI_iterator;
static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
static inline PHI_iterator PHI_end(PhiT *PHI) {
return PHI_iterator(PHI, true);
}
/// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
/// vector, set Info->NumPreds, and allocate space in Info->Preds.
static void FindPredecessorBlocks(BasicBlock *BB,
SmallVectorImpl<BasicBlock*> *Preds) {
// We can get our predecessor info by walking the pred_iterator list,
// but it is relatively slow. If we already have PHI nodes in this
// block, walk one of them to get the predecessor list instead.
if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
Preds->push_back(SomePhi->getIncomingBlock(PI));
} else {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
Preds->push_back(*PI);
}
}
/// GetUndefVal - Get an undefined value of the same type as the value
/// being handled.
static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
return UndefValue::get(Updater->PrototypeValue->getType());
}
/// CreateEmptyPHI - Create a new PHI instruction in the specified block.
/// Reserve space for the operands but do not fill them in yet.
static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
SSAUpdater *Updater) {
PHINode *PHI = PHINode::Create(Updater->PrototypeValue->getType(),
Updater->PrototypeValue->getName(),
&BB->front());
PHI->reserveOperandSpace(NumPreds);
return PHI;
}
/// AddPHIOperand - Add the specified value as an operand of the PHI for
/// the specified predecessor block.
static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
PHI->addIncoming(Val, Pred);
}
/// InstrIsPHI - Check if an instruction is a PHI.
///
static PHINode *InstrIsPHI(Instruction *I) {
return dyn_cast<PHINode>(I);
}
/// ValueIsPHI - Check if a value is a PHI.
///
static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
return dyn_cast<PHINode>(Val);
}
/// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
/// operands, i.e., it was just added.
static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
PHINode *PHI = ValueIsPHI(Val, Updater);
if (PHI && PHI->getNumIncomingValues() == 0)
return PHI;
return 0;
}
/// GetPHIValue - For the specified PHI instruction, return the value
/// that it defines.
static Value *GetPHIValue(PHINode *PHI) {
return PHI;
}
};
} // End llvm namespace
/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
/// for the specified BB and if so, return it. If not, construct SSA form by
/// first calculating the required placement of PHIs and then inserting new
@ -240,418 +325,6 @@ Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
if (Value *V = AvailableVals[BB])
return V;
// Pool allocation used internally by GetValueAtEndOfBlock.
BumpPtrAllocator Allocator;
BBMapTy BBMapObj;
BM = &BBMapObj;
SmallVector<BBInfo*, 100> BlockList;
BuildBlockList(BB, &BlockList, &Allocator);
// Special case: bail out if BB is unreachable.
if (BlockList.size() == 0) {
BM = 0;
return UndefValue::get(PrototypeValue->getType());
}
FindDominators(&BlockList);
FindPHIPlacement(&BlockList);
FindAvailableVals(&BlockList);
BM = 0;
return BBMapObj[BB]->DefBB->AvailableVal;
}
/// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
/// vector, set Info->NumPreds, and allocate space in Info->Preds.
static void FindPredecessorBlocks(SSAUpdater::BBInfo *Info,
SmallVectorImpl<BasicBlock*> *Preds,
BumpPtrAllocator *Allocator) {
// We can get our predecessor info by walking the pred_iterator list,
// but it is relatively slow. If we already have PHI nodes in this
// block, walk one of them to get the predecessor list instead.
BasicBlock *BB = Info->BB;
if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
Preds->push_back(SomePhi->getIncomingBlock(PI));
} else {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
Preds->push_back(*PI);
}
Info->NumPreds = Preds->size();
Info->Preds = static_cast<SSAUpdater::BBInfo**>
(Allocator->Allocate(Info->NumPreds * sizeof(SSAUpdater::BBInfo*),
AlignOf<SSAUpdater::BBInfo*>::Alignment));
}
/// BuildBlockList - Starting from the specified basic block, traverse back
/// through its predecessors until reaching blocks with known values. Create
/// BBInfo structures for the blocks and append them to the block list.
void SSAUpdater::BuildBlockList(BasicBlock *BB, BlockListTy *BlockList,
BumpPtrAllocator *Allocator) {
AvailableValsTy &AvailableVals = getAvailableVals(AV);
BBMapTy *BBMap = getBBMap(BM);
SmallVector<BBInfo*, 10> RootList;
SmallVector<BBInfo*, 64> WorkList;
BBInfo *Info = new (*Allocator) BBInfo(BB, 0);
(*BBMap)[BB] = Info;
WorkList.push_back(Info);
// Search backward from BB, creating BBInfos along the way and stopping when
// reaching blocks that define the value. Record those defining blocks on
// the RootList.
SmallVector<BasicBlock*, 10> Preds;
while (!WorkList.empty()) {
Info = WorkList.pop_back_val();
Preds.clear();
FindPredecessorBlocks(Info, &Preds, Allocator);
// Treat an unreachable predecessor as a definition with 'undef'.
if (Info->NumPreds == 0) {
Info->AvailableVal = UndefValue::get(PrototypeValue->getType());
Info->DefBB = Info;
RootList.push_back(Info);
continue;
}
for (unsigned p = 0; p != Info->NumPreds; ++p) {
BasicBlock *Pred = Preds[p];
// Check if BBMap already has a BBInfo for the predecessor block.
BBMapTy::value_type &BBMapBucket = BBMap->FindAndConstruct(Pred);
if (BBMapBucket.second) {
Info->Preds[p] = BBMapBucket.second;
continue;
}
// Create a new BBInfo for the predecessor.
Value *PredVal = AvailableVals.lookup(Pred);
BBInfo *PredInfo = new (*Allocator) BBInfo(Pred, PredVal);
BBMapBucket.second = PredInfo;
Info->Preds[p] = PredInfo;
if (PredInfo->AvailableVal) {
RootList.push_back(PredInfo);
continue;
}
WorkList.push_back(PredInfo);
}
}
// Now that we know what blocks are backwards-reachable from the starting
// block, do a forward depth-first traversal to assign postorder numbers
// to those blocks.
BBInfo *PseudoEntry = new (*Allocator) BBInfo(0, 0);
unsigned BlkNum = 1;
// Initialize the worklist with the roots from the backward traversal.
while (!RootList.empty()) {
Info = RootList.pop_back_val();
Info->IDom = PseudoEntry;
Info->BlkNum = -1;
WorkList.push_back(Info);
}
while (!WorkList.empty()) {
Info = WorkList.back();
if (Info->BlkNum == -2) {
// All the successors have been handled; assign the postorder number.
Info->BlkNum = BlkNum++;
// If not a root, put it on the BlockList.
if (!Info->AvailableVal)
BlockList->push_back(Info);
WorkList.pop_back();
continue;
}
// Leave this entry on the worklist, but set its BlkNum to mark that its
// successors have been put on the worklist. When it returns to the top
// the list, after handling its successors, it will be assigned a number.
Info->BlkNum = -2;
// Add unvisited successors to the work list.
for (succ_iterator SI = succ_begin(Info->BB), E = succ_end(Info->BB);
SI != E; ++SI) {
BBInfo *SuccInfo = (*BBMap)[*SI];
if (!SuccInfo || SuccInfo->BlkNum)
continue;
SuccInfo->BlkNum = -1;
WorkList.push_back(SuccInfo);
}
}
PseudoEntry->BlkNum = BlkNum;
}
/// IntersectDominators - This is the dataflow lattice "meet" operation for
/// finding dominators. Given two basic blocks, it walks up the dominator
/// tree until it finds a common dominator of both. It uses the postorder
/// number of the blocks to determine how to do that.
static SSAUpdater::BBInfo *IntersectDominators(SSAUpdater::BBInfo *Blk1,
SSAUpdater::BBInfo *Blk2) {
while (Blk1 != Blk2) {
while (Blk1->BlkNum < Blk2->BlkNum) {
Blk1 = Blk1->IDom;
if (!Blk1)
return Blk2;
}
while (Blk2->BlkNum < Blk1->BlkNum) {
Blk2 = Blk2->IDom;
if (!Blk2)
return Blk1;
}
}
return Blk1;
}
/// FindDominators - Calculate the dominator tree for the subset of the CFG
/// corresponding to the basic blocks on the BlockList. This uses the
/// algorithm from: "A Simple, Fast Dominance Algorithm" by Cooper, Harvey and
/// Kennedy, published in Software--Practice and Experience, 2001, 4:1-10.
/// Because the CFG subset does not include any edges leading into blocks that
/// define the value, the results are not the usual dominator tree. The CFG
/// subset has a single pseudo-entry node with edges to a set of root nodes
/// for blocks that define the value. The dominators for this subset CFG are
/// not the standard dominators but they are adequate for placing PHIs within
/// the subset CFG.
void SSAUpdater::FindDominators(BlockListTy *BlockList) {
bool Changed;
do {
Changed = false;
// Iterate over the list in reverse order, i.e., forward on CFG edges.
for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
E = BlockList->rend(); I != E; ++I) {
BBInfo *Info = *I;
// Start with the first predecessor.
assert(Info->NumPreds > 0 && "unreachable block");
BBInfo *NewIDom = Info->Preds[0];
// Iterate through the block's other predecessors.
for (unsigned p = 1; p != Info->NumPreds; ++p) {
BBInfo *Pred = Info->Preds[p];
NewIDom = IntersectDominators(NewIDom, Pred);
}
// Check if the IDom value has changed.
if (NewIDom != Info->IDom) {
Info->IDom = NewIDom;
Changed = true;
}
}
} while (Changed);
}
/// IsDefInDomFrontier - Search up the dominator tree from Pred to IDom for
/// any blocks containing definitions of the value. If one is found, then the
/// successor of Pred is in the dominance frontier for the definition, and
/// this function returns true.
static bool IsDefInDomFrontier(const SSAUpdater::BBInfo *Pred,
const SSAUpdater::BBInfo *IDom) {
for (; Pred != IDom; Pred = Pred->IDom) {
if (Pred->DefBB == Pred)
return true;
}
return false;
}
/// FindPHIPlacement - PHIs are needed in the iterated dominance frontiers of
/// the known definitions. Iteratively add PHIs in the dom frontiers until
/// nothing changes. Along the way, keep track of the nearest dominating
/// definitions for non-PHI blocks.
void SSAUpdater::FindPHIPlacement(BlockListTy *BlockList) {
bool Changed;
do {
Changed = false;
// Iterate over the list in reverse order, i.e., forward on CFG edges.
for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
E = BlockList->rend(); I != E; ++I) {
BBInfo *Info = *I;
// If this block already needs a PHI, there is nothing to do here.
if (Info->DefBB == Info)
continue;
// Default to use the same def as the immediate dominator.
BBInfo *NewDefBB = Info->IDom->DefBB;
for (unsigned p = 0; p != Info->NumPreds; ++p) {
if (IsDefInDomFrontier(Info->Preds[p], Info->IDom)) {
// Need a PHI here.
NewDefBB = Info;
break;
}
}
// Check if anything changed.
if (NewDefBB != Info->DefBB) {
Info->DefBB = NewDefBB;
Changed = true;
}
}
} while (Changed);
}
/// FindAvailableVal - If this block requires a PHI, first check if an existing
/// PHI matches the PHI placement and reaching definitions computed earlier,
/// and if not, create a new PHI. Visit all the block's predecessors to
/// calculate the available value for each one and fill in the incoming values
/// for a new PHI.
void SSAUpdater::FindAvailableVals(BlockListTy *BlockList) {
AvailableValsTy &AvailableVals = getAvailableVals(AV);
// Go through the worklist in forward order (i.e., backward through the CFG)
// and check if existing PHIs can be used. If not, create empty PHIs where
// they are needed.
for (BlockListTy::iterator I = BlockList->begin(), E = BlockList->end();
I != E; ++I) {
BBInfo *Info = *I;
// Check if there needs to be a PHI in BB.
if (Info->DefBB != Info)
continue;
// Look for an existing PHI.
FindExistingPHI(Info->BB, BlockList);
if (Info->AvailableVal)
continue;
PHINode *PHI = PHINode::Create(PrototypeValue->getType(),
PrototypeValue->getName(),
&Info->BB->front());
PHI->reserveOperandSpace(Info->NumPreds);
Info->AvailableVal = PHI;
AvailableVals[Info->BB] = PHI;
}
// Now go back through the worklist in reverse order to fill in the arguments
// for any new PHIs added in the forward traversal.
for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
E = BlockList->rend(); I != E; ++I) {
BBInfo *Info = *I;
if (Info->DefBB != Info) {
// Record the available value at join nodes to speed up subsequent
// uses of this SSAUpdater for the same value.
if (Info->NumPreds > 1)
AvailableVals[Info->BB] = Info->DefBB->AvailableVal;
continue;
}
// Check if this block contains a newly added PHI.
PHINode *PHI = dyn_cast<PHINode>(Info->AvailableVal);
if (!PHI || PHI->getNumIncomingValues() == Info->NumPreds)
continue;
// Iterate through the block's predecessors.
for (unsigned p = 0; p != Info->NumPreds; ++p) {
BBInfo *PredInfo = Info->Preds[p];
BasicBlock *Pred = PredInfo->BB;
// Skip to the nearest preceding definition.
if (PredInfo->DefBB != PredInfo)
PredInfo = PredInfo->DefBB;
PHI->addIncoming(PredInfo->AvailableVal, Pred);
}
DEBUG(dbgs() << " Inserted PHI: " << *PHI << "\n");
// If the client wants to know about all new instructions, tell it.
if (InsertedPHIs) InsertedPHIs->push_back(PHI);
}
}
/// FindExistingPHI - Look through the PHI nodes in a block to see if any of
/// them match what is needed.
void SSAUpdater::FindExistingPHI(BasicBlock *BB, BlockListTy *BlockList) {
PHINode *SomePHI;
for (BasicBlock::iterator It = BB->begin();
(SomePHI = dyn_cast<PHINode>(It)); ++It) {
if (CheckIfPHIMatches(SomePHI)) {
RecordMatchingPHI(SomePHI);
break;
}
// Match failed: clear all the PHITag values.
for (BlockListTy::iterator I = BlockList->begin(), E = BlockList->end();
I != E; ++I)
(*I)->PHITag = 0;
}
}
/// CheckIfPHIMatches - Check if a PHI node matches the placement and values
/// in the BBMap.
bool SSAUpdater::CheckIfPHIMatches(PHINode *PHI) {
BBMapTy *BBMap = getBBMap(BM);
SmallVector<PHINode*, 20> WorkList;
WorkList.push_back(PHI);
// Mark that the block containing this PHI has been visited.
(*BBMap)[PHI->getParent()]->PHITag = PHI;
while (!WorkList.empty()) {
PHI = WorkList.pop_back_val();
// Iterate through the PHI's incoming values.
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
Value *IncomingVal = PHI->getIncomingValue(i);
BBInfo *PredInfo = (*BBMap)[PHI->getIncomingBlock(i)];
// Skip to the nearest preceding definition.
if (PredInfo->DefBB != PredInfo)
PredInfo = PredInfo->DefBB;
// Check if it matches the expected value.
if (PredInfo->AvailableVal) {
if (IncomingVal == PredInfo->AvailableVal)
continue;
return false;
}
// Check if the value is a PHI in the correct block.
PHINode *IncomingPHIVal = dyn_cast<PHINode>(IncomingVal);
if (!IncomingPHIVal || IncomingPHIVal->getParent() != PredInfo->BB)
return false;
// If this block has already been visited, check if this PHI matches.
if (PredInfo->PHITag) {
if (IncomingPHIVal == PredInfo->PHITag)
continue;
return false;
}
PredInfo->PHITag = IncomingPHIVal;
WorkList.push_back(IncomingPHIVal);
}
}
return true;
}
/// RecordMatchingPHI - For a PHI node that matches, record it and its input
/// PHIs in both the BBMap and the AvailableVals mapping.
void SSAUpdater::RecordMatchingPHI(PHINode *PHI) {
BBMapTy *BBMap = getBBMap(BM);
AvailableValsTy &AvailableVals = getAvailableVals(AV);
SmallVector<PHINode*, 20> WorkList;
WorkList.push_back(PHI);
// Record this PHI.
BasicBlock *BB = PHI->getParent();
AvailableVals[BB] = PHI;
(*BBMap)[BB]->AvailableVal = PHI;
while (!WorkList.empty()) {
PHI = WorkList.pop_back_val();
// Iterate through the PHI's incoming values.
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
PHINode *IncomingPHIVal = dyn_cast<PHINode>(PHI->getIncomingValue(i));
if (!IncomingPHIVal) continue;
BB = IncomingPHIVal->getParent();
BBInfo *Info = (*BBMap)[BB];
if (!Info || Info->AvailableVal)
continue;
// Record the PHI and add it to the worklist.
AvailableVals[BB] = IncomingPHIVal;
Info->AvailableVal = IncomingPHIVal;
WorkList.push_back(IncomingPHIVal);
}
}
SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
return Impl.GetValue(BB);
}