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Fill out codegen SSA updater. It's not yet tested. 

llvm-svn: 90395
This commit is contained in:
Evan Cheng 2009-12-03 02:31:43 +00:00
parent 2ca285fc5c
commit 7145382389
4 changed files with 270 additions and 15 deletions
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5
llvm/include/llvm/CodeGen/MachineInstr.h
View File

@ -320,6 +320,11 @@ public:
/// loads the instruction does are invariant (if it does multiple loads).
bool isInvariantLoad(AliasAnalysis *AA) const;
/// isConstantValuePHI - If the specified instruction is a PHI that always
/// merges together the same virtual register, return the register, otherwise
/// return 0.
unsigned isConstantValuePHI() const;
//
// Debugging support
//

29
llvm/include/llvm/CodeGen/MachineSSAUpdater.h
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@ -16,13 +16,18 @@
namespace llvm {
class MachineBasicBlock;
class MachineFunction;
class MachineInstr;
class MachineOperand;
class MachineRegisterInfo;
class TargetInstrInfo;
class TargetRegisterClass;
template<typename T> class SmallVectorImpl;
/// SSAUpdater - This class updates SSA form for a set of values defined in
/// multiple blocks. This is used when code duplication or another unstructured
/// transformation wants to rewrite a set of uses of one value with uses of a
/// set of values.
/// 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 {
/// 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.
@ -35,18 +40,28 @@ class MachineSSAUpdater {
//std::vector<std::pair<MachineBasicBlock*, unsigned > > IncomingPredInfo;
void *IPI;
/// VR - Current virtual register whose uses are being updated.
unsigned VR;
/// VRC - Register class of the current virtual register.
const TargetRegisterClass *VRC;
/// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI
/// nodes that it creates to the vector.
SmallVectorImpl<MachineInstr*> *InsertedPHIs;
const TargetInstrInfo *TII;
MachineRegisterInfo *MRI;
public:
/// MachineSSAUpdater constructor. If InsertedPHIs is specified, it will be
/// filled in with all PHI Nodes created by rewriting.
explicit MachineSSAUpdater(SmallVectorImpl<MachineInstr*> *InsertedPHIs = 0);
explicit MachineSSAUpdater(MachineFunction &MF,
SmallVectorImpl<MachineInstr*> *InsertedPHIs = 0);
~MachineSSAUpdater();
/// Initialize - Reset this object to get ready for a new set of SSA
/// updates.
void Initialize();
void Initialize(unsigned V);
/// AddAvailableValue - Indicate that a rewritten value is available at the
/// end of the specified block with the specified value.
@ -86,7 +101,7 @@ public:
/// will not work if the use is supposed to be rewritten to a value defined in
/// the same block as the use, but above it. Any 'AddAvailableValue's added
/// for the use's block will be considered to be below it.
void RewriteUse(unsigned &U);
void RewriteUse(MachineOperand &U);
private:
unsigned GetValueAtEndOfBlockInternal(MachineBasicBlock *BB);

14
llvm/lib/CodeGen/MachineInstr.cpp
View File

@ -1058,6 +1058,20 @@ bool MachineInstr::isInvariantLoad(AliasAnalysis *AA) const {
return true;
}
/// isConstantValuePHI - If the specified instruction is a PHI that always
/// merges together the same virtual register, return the register, otherwise
/// return 0.
unsigned MachineInstr::isConstantValuePHI() const {
if (getOpcode() != TargetInstrInfo::PHI)
return 0;
unsigned Reg = getOperand(1).getReg();
for (unsigned i = 3, e = getNumOperands(); i < e; i += 2)
if (getOperand(i).getReg() != Reg)
return 0;
return Reg;
}
void MachineInstr::dump() const {
errs() << " " << *this;
}

237
llvm/lib/CodeGen/MachineSSAUpdater.cpp
View File

@ -7,16 +7,25 @@
//
//===----------------------------------------------------------------------===//
//
// This file implements the MachineSSAUpdater class.
// This file implements the MachineSSAUpdater class. It's based on SSAUpdater
// class in lib/Transforms/Utils.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/MachineSSAUpdater.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/ADT/DenseMap.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 DenseMap<MachineBasicBlock*, unsigned> AvailableValsTy;
typedef std::vector<std::pair<MachineBasicBlock*, unsigned> >
IncomingPredInfoTy;
@ -29,8 +38,12 @@ static IncomingPredInfoTy &getIncomingPredInfo(void *IPI) {
}
MachineSSAUpdater::MachineSSAUpdater(SmallVectorImpl<MachineInstr*> *NewPHI)
: AV(0), IPI(0), InsertedPHIs(NewPHI) {}
MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
SmallVectorImpl<MachineInstr*> *NewPHI)
: AV(0), IPI(0), InsertedPHIs(NewPHI) {
TII = MF.getTarget().getInstrInfo();
MRI = &MF.getRegInfo();
}
MachineSSAUpdater::~MachineSSAUpdater() {
delete &getAvailableVals(AV);
@ -39,7 +52,7 @@ MachineSSAUpdater::~MachineSSAUpdater() {
/// Initialize - Reset this object to get ready for a new set of SSA
/// updates. ProtoValue is the value used to name PHI nodes.
void MachineSSAUpdater::Initialize() {
void MachineSSAUpdater::Initialize(unsigned V) {
if (AV == 0)
AV = new AvailableValsTy();
else
@ -49,6 +62,9 @@ void MachineSSAUpdater::Initialize() {
IPI = new IncomingPredInfoTy();
else
getIncomingPredInfo(IPI).clear();
VR = V;
VRC = MRI->getRegClass(VR);
}
/// HasValueForBlock - Return true if the MachineSSAUpdater already has a value for
@ -69,6 +85,18 @@ unsigned MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) {
return GetValueAtEndOfBlockInternal(BB);
}
/// InsertNewPHI - Insert an empty PHI instruction which define a value of the
/// given register class at the start of the specified basic block. It returns
/// the virtual register defined by the PHI instruction.
static
MachineInstr *InsertNewPHI(MachineBasicBlock *BB, const TargetRegisterClass *RC,
MachineRegisterInfo *MRI, const TargetInstrInfo *TII) {
unsigned NewVR = MRI->createVirtualRegister(RC);
return BuildMI(*BB, BB->front(), BB->front().getDebugLoc(),
TII->get(TargetInstrInfo::PHI), NewVR);
}
/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
/// is live in the middle of the specified block.
///
@ -89,14 +117,86 @@ unsigned MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) {
/// merge the appropriate values, and this value isn't live out of the block.
///
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))
return GetValueAtEndOfBlock(BB);
if (BB->pred_empty())
llvm_unreachable("Unreachable block!");
// Otherwise, we have the hard case. Get the live-in values for each
// predecessor.
SmallVector<std::pair<MachineBasicBlock*, unsigned>, 8> PredValues;
unsigned SingularValue = 0;
bool isFirstPred = true;
for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
E = BB->pred_end(); PI != E; ++PI) {
MachineBasicBlock *PredBB = *PI;
unsigned PredVal = GetValueAtEndOfBlockInternal(PredBB);
PredValues.push_back(std::make_pair(PredBB, PredVal));
// Compute SingularValue.
if (isFirstPred) {
SingularValue = PredVal;
isFirstPred = false;
} else if (PredVal != SingularValue)
SingularValue = 0;
}
// Otherwise, if all the merged values are the same, just use it.
if (SingularValue != 0)
return SingularValue;
// Otherwise, we do need a PHI: insert one now.
MachineInstr *InsertedPHI = InsertNewPHI(BB, VRC, MRI, TII);
// Fill in all the predecessors of the PHI.
MachineInstrBuilder MIB(InsertedPHI);
for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
MIB.addReg(PredValues[i].second).addMBB(PredValues[i].first);
// 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()) {
InsertedPHI->eraseFromParent();
return ConstVal;
}
// If the client wants to know about all new instructions, tell it.
if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
DEBUG(errs() << " Inserted PHI: " << *InsertedPHI << "\n");
return InsertedPHI->getOperand(0).getReg();
}
static
MachineBasicBlock *findCorrespondingPred(const MachineInstr *MI,
MachineOperand *U) {
for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
if (&MI->getOperand(i) == U)
return MI->getOperand(i+1).getMBB();
}
llvm_unreachable("MachineOperand::getParent() failure?");
return 0;
}
/// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
/// which use their value in the corresponding predecessor.
void MachineSSAUpdater::RewriteUse(unsigned &U) {
}
void MachineSSAUpdater::RewriteUse(MachineOperand &U) {
MachineInstr *UseMI = U.getParent();
unsigned NewVR = 0;
if (UseMI->getOpcode() == TargetInstrInfo::PHI) {
MachineBasicBlock *SourceBB = findCorrespondingPred(UseMI, &U);
NewVR = GetValueAtEndOfBlock(SourceBB);
} else {
NewVR = GetValueInMiddleOfBlock(UseMI->getParent());
}
U.setReg(NewVR);
}
/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
/// for the specified BB and if so, return it. If not, construct SSA form by
@ -104,5 +204,126 @@ void MachineSSAUpdater::RewriteUse(unsigned &U) {
/// where the value is available.
///
unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
return 0;
AvailableValsTy &AvailableVals = getAvailableVals(AV);
// Query AvailableVals by doing an insertion of null.
std::pair<AvailableValsTy::iterator, bool> InsertRes =
AvailableVals.insert(std::make_pair(BB, 0));
// 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;
// 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.
MachineInstr *NewPHI = InsertNewPHI(BB, VRC, MRI, TII);
unsigned NewVR = NewPHI->getOperand(0).getReg();
InsertRes.first->second = NewVR;
return NewVR;
}
if (BB->pred_empty())
llvm_unreachable("Unreachable block!");
// 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();
// 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;
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));
// Compute SingularValue.
if (isFirstPred) {
SingularValue = PredVal;
isFirstPred = false;
} else if (PredVal != SingularValue)
SingularValue = 0;
}
/// 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];
// 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?");
MRI->replaceRegWith(InsertedVal, SingularValue);
OldVal->eraseFromParent();
} else {
InsertedVal = SingularValue;
}
// Drop the entries we added in IncomingPredInfo to restore the stack.
IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
IncomingPredInfo.end());
return InsertedVal;
}
// Otherwise, we do need a PHI: insert one now if we don't already have one.
MachineInstr *InsertedPHI;
if (InsertedVal == 0) {
InsertedPHI = InsertNewPHI(BB, VRC, MRI, TII);
InsertedVal = InsertedPHI->getOperand(0).getReg();
} else {
InsertedPHI = MRI->getVRegDef(InsertedVal);
}
// 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);
// Drop the entries we added in IncomingPredInfo to restore the stack.
IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
IncomingPredInfo.end());
// 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(errs() << " Inserted PHI: " << *InsertedPHI << "\n");
// If the client wants to know about all new instructions, tell it.
if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
}
return InsertedVal;
}