[llvm-commits] [llvm] r102353 - in /llvm/trunk: include/llvm/CodeGen/MachineSSAUpdater.h lib/CodeGen/MachineSSAUpdater.cpp
Bob Wilson
bob.wilson at apple.com
Mon Apr 26 10:40:49 PDT 2010
Author: bwilson
Date: Mon Apr 26 12:40:49 2010
New Revision: 102353
URL: http://llvm.org/viewvc/llvm-project?rev=102353&view=rev
Log:
Update MachineSSAUpdater with the same changes I made for the IR-level
SSAUpdater. I'm going to try to refactor this to share most of the code
between them.
Modified:
llvm/trunk/include/llvm/CodeGen/MachineSSAUpdater.h
llvm/trunk/lib/CodeGen/MachineSSAUpdater.cpp
Modified: llvm/trunk/include/llvm/CodeGen/MachineSSAUpdater.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/MachineSSAUpdater.h?rev=102353&r1=102352&r2=102353&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/MachineSSAUpdater.h (original)
+++ llvm/trunk/include/llvm/CodeGen/MachineSSAUpdater.h Mon Apr 26 12:40:49 2010
@@ -23,22 +23,27 @@
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 @@
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
};
Modified: llvm/trunk/lib/CodeGen/MachineSSAUpdater.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineSSAUpdater.cpp?rev=102353&r1=102352&r2=102353&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineSSAUpdater.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineSSAUpdater.cpp Mon Apr 26 12:40:49 2010
@@ -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 @@
else
getAvailableVals(AV).clear();
- if (IPI == 0)
- IPI = new IncomingPredInfoTy();
- else
- getIncomingPredInfo(IPI).clear();
-
VR = V;
VRC = MRI->getRegClass(VR);
}
@@ -127,7 +138,7 @@
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 @@
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 @@
/// 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));
-
- // 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.
- 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()) {
+ // 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);
- 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();
-
- // 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;
+ 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) {
- 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));
+}
+
+/// 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;
+ }
- /// 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?");
- ReplaceRegWith(InsertedVal, SingularValue);
- OldVal->eraseFromParent();
- }
-
- InsertedVal = SingularValue;
-
- // Drop the entries we added in IncomingPredInfo to restore the stack.
- IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
- IncomingPredInfo.end());
- return InsertedVal;
+ 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;
+ }
- // 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);
+ // 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;
+}
- // 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());
+/// 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);
}
+}
+
+/// 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);
- return InsertedVal;
+ // 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);
+ }
+ }
}
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