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Update MachineSSAUpdater with the same changes I made for the IR-level

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SSAUpdater.  I'm going to try to refactor this to share most of the code
between them.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@102353 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bob Wilson 2010-04-26 17:40:49 +00:00
parent 7c8e7965e1
commit 211678a0d7
2 changed files with 446 additions and 126 deletions
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24
include/llvm/CodeGen/MachineSSAUpdater.h
View File

@ -23,22 +23,27 @@ namespace llvm {
class TargetInstrInfo;
class TargetRegisterClass;
template<typename T> class SmallVectorImpl;
class BumpPtrAllocator;
/// MachineSSAUpdater - This class updates SSA form for a set of virtual
/// registers defined in multiple blocks. This is used when code duplication
/// 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;
private:
/// AvailableVals - This keeps track of which value to use on a per-block
/// basis. When we insert PHI nodes, we keep track of them here.
//typedef DenseMap<MachineBasicBlock*, unsigned > AvailableValsTy;
void *AV;
/// IncomingPredInfo - We use this as scratch space when doing our recursive
/// walk. This should only be used in GetValueInBlockInternal, normally it
/// should be empty.
//std::vector<std::pair<MachineBasicBlock*, unsigned > > IncomingPredInfo;
void *IPI;
/// 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;
@ -106,6 +111,15 @@ 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
};

548
lib/CodeGen/MachineSSAUpdater.cpp
View File

@ -21,34 +21,50 @@
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/AlignOf.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
typedef DenseMap<MachineBasicBlock*, unsigned> AvailableValsTy;
typedef std::vector<std::pair<MachineBasicBlock*, unsigned> >
IncomingPredInfoTy;
/// 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 IncomingPredInfoTy &getIncomingPredInfo(void *IPI) {
return *static_cast<IncomingPredInfoTy*>(IPI);
static BBMapTy *getBBMap(void *BM) {
return static_cast<BBMapTy*>(BM);
}
MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
SmallVectorImpl<MachineInstr*> *NewPHI)
: AV(0), IPI(0), InsertedPHIs(NewPHI) {
: AV(0), BM(0), InsertedPHIs(NewPHI) {
TII = MF.getTarget().getInstrInfo();
MRI = &MF.getRegInfo();
}
MachineSSAUpdater::~MachineSSAUpdater() {
delete &getAvailableVals(AV);
delete &getIncomingPredInfo(IPI);
}
/// Initialize - Reset this object to get ready for a new set of SSA
@ -59,11 +75,6 @@ void MachineSSAUpdater::Initialize(unsigned V) {
else
getAvailableVals(AV).clear();
if (IPI == 0)
IPI = new IncomingPredInfoTy();
else
getIncomingPredInfo(IPI).clear();
VR = V;
VRC = MRI->getRegClass(VR);
}
@ -127,7 +138,7 @@ MachineInstr *InsertNewDef(unsigned Opcode,
unsigned NewVR = MRI->createVirtualRegister(RC);
return BuildMI(*BB, I, DebugLoc(), TII->get(Opcode), NewVR);
}
/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
/// is live in the middle of the specified block.
///
@ -150,7 +161,7 @@ MachineInstr *InsertNewDef(unsigned Opcode,
unsigned MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB) {
// If there is no definition of the renamed variable in this block, just use
// GetValueAtEndOfBlock to do our work.
if (!getAvailableVals(AV).count(BB))
if (!HasValueForBlock(BB))
return GetValueAtEndOfBlockInternal(BB);
// If there are no predecessors, just return undef.
@ -254,141 +265,436 @@ void MachineSSAUpdater::ReplaceRegWith(unsigned OldReg, unsigned NewReg) {
/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
/// for the specified BB and if so, return it. If not, construct SSA form by
/// walking predecessors inserting PHI nodes as needed until we get to a block
/// where the value is available.
///
/// first calculating the required placement of PHIs and then inserting new
/// PHIs where needed.
unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
AvailableValsTy &AvailableVals = getAvailableVals(AV);
if (unsigned V = AvailableVals[BB])
return V;
// Query AvailableVals by doing an insertion of null.
std::pair<AvailableValsTy::iterator, bool> InsertRes =
AvailableVals.insert(std::make_pair(BB, 0));
// Pool allocation used internally by GetValueAtEndOfBlock.
BumpPtrAllocator Allocator;
BBMapTy BBMapObj;
BM = &BBMapObj;
// Handle the case when the insertion fails because we have already seen BB.
if (!InsertRes.second) {
// If the insertion failed, there are two cases. The first case is that the
// value is already available for the specified block. If we get this, just
// return the value.
if (InsertRes.first->second != 0)
return InsertRes.first->second;
SmallVector<BBInfo*, 100> BlockList;
BuildBlockList(BB, &BlockList, &Allocator);
// Otherwise, if the value we find is null, then this is the value is not
// known but it is being computed elsewhere in our recursion. This means
// that we have a cycle. Handle this by inserting a PHI node and returning
// it. When we get back to the first instance of the recursion we will fill
// in the PHI node.
MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->front();
MachineInstr *NewPHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
VRC, MRI,TII);
unsigned NewVR = NewPHI->getOperand(0).getReg();
InsertRes.first->second = NewVR;
return NewVR;
}
// If there are no predecessors, then we must have found an unreachable block
// just return 'undef'. Since there are no predecessors, InsertRes must not
// be invalidated.
if (BB->pred_empty()) {
// 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);
return InsertRes.first->second = NewDef->getOperand(0).getReg();
unsigned V = NewDef->getOperand(0).getReg();
AvailableVals[BB] = V;
return V;
}
// Okay, the value isn't in the map and we just inserted a null in the entry
// to indicate that we're processing the block. Since we have no idea what
// value is in this block, we have to recurse through our predecessors.
//
// While we're walking our predecessors, we keep track of them in a vector,
// then insert a PHI node in the end if we actually need one. We could use a
// smallvector here, but that would take a lot of stack space for every level
// of the recursion, just use IncomingPredInfo as an explicit stack.
IncomingPredInfoTy &IncomingPredInfo = getIncomingPredInfo(IPI);
unsigned FirstPredInfoEntry = IncomingPredInfo.size();
FindDominators(&BlockList);
FindPHIPlacement(&BlockList);
FindAvailableVals(&BlockList);
// As we're walking the predecessors, keep track of whether they are all
// producing the same value. If so, this value will capture it, if not, it
// will get reset to null. We distinguish the no-predecessor case explicitly
// below.
unsigned SingularValue = 0;
bool isFirstPred = true;
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) {
MachineBasicBlock *PredBB = *PI;
unsigned PredVal = GetValueAtEndOfBlockInternal(PredBB);
IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal));
E = BB->pred_end(); PI != E; ++PI)
Preds->push_back(*PI);
// Compute SingularValue.
if (isFirstPred) {
SingularValue = PredVal;
isFirstPred = false;
} else if (PredVal != SingularValue)
SingularValue = 0;
}
Info->NumPreds = Preds->size();
Info->Preds = static_cast<MachineSSAUpdater::BBInfo**>
(Allocator->Allocate(Info->NumPreds * sizeof(MachineSSAUpdater::BBInfo*),
AlignOf<MachineSSAUpdater::BBInfo*>::Alignment));
}
/// Look up BB's entry in AvailableVals. 'InsertRes' may be invalidated. If
/// this block is involved in a loop, a no-entry PHI node will have been
/// inserted as InsertedVal. Otherwise, we'll still have the null we inserted
/// above.
unsigned &InsertedVal = AvailableVals[BB];
/// 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;
// If all the predecessor values are the same then we don't need to insert a
// PHI. This is the simple and common case.
if (SingularValue) {
// If a PHI node got inserted, replace it with the singlar value and delete
// it.
if (InsertedVal) {
MachineInstr *OldVal = MRI->getVRegDef(InsertedVal);
// Be careful about dead loops. These RAUW's also update InsertedVal.
assert(InsertedVal != SingularValue && "Dead loop?");
ReplaceRegWith(InsertedVal, SingularValue);
OldVal->eraseFromParent();
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;
}
InsertedVal = SingularValue;
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;
}
// Drop the entries we added in IncomingPredInfo to restore the stack.
IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
IncomingPredInfo.end());
return InsertedVal;
// 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;
// Otherwise, we do need a PHI: insert one now if we don't already have one.
MachineInstr *InsertedPHI;
if (InsertedVal == 0) {
MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->front();
InsertedPHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
VRC, MRI, TII);
InsertedVal = InsertedPHI->getOperand(0).getReg();
} else {
InsertedPHI = MRI->getVRegDef(InsertedVal);
// 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);
}
// Fill in all the predecessors of the PHI.
MachineInstrBuilder MIB(InsertedPHI);
for (IncomingPredInfoTy::iterator I =
IncomingPredInfo.begin()+FirstPredInfoEntry,
E = IncomingPredInfo.end(); I != E; ++I)
MIB.addReg(I->second).addMBB(I->first);
while (!WorkList.empty()) {
Info = WorkList.back();
// Drop the entries we added in IncomingPredInfo to restore the stack.
IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
IncomingPredInfo.end());
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);
}
// See if the PHI node can be merged to a single value. This can happen in
// loop cases when we get a PHI of itself and one other value.
if (unsigned ConstVal = InsertedPHI->isConstantValuePHI()) {
MRI->replaceRegWith(InsertedVal, ConstVal);
InsertedPHI->eraseFromParent();
InsertedVal = ConstVal;
} else {
DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
// If the client wants to know about all new instructions, tell it.
if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
}
return InsertedVal;
}
/// 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);
}
}
}