llvm-6502/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
2004-09-15 01:02:54 +00:00

745 lines
31 KiB
C++

//===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file promote memory references to be register references. It promotes
// alloca instructions which only have loads and stores as uses (or that have
// PHI nodes which are only loaded from). An alloca is transformed by using
// dominator frontiers to place PHI nodes, then traversing the function in
// depth-first order to rewrite loads and stores as appropriate. This is just
// the standard SSA construction algorithm to construct "pruned" SSA form.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Constant.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/AliasSetTracker.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/StableBasicBlockNumbering.h"
#include <algorithm>
using namespace llvm;
/// isAllocaPromotable - Return true if this alloca is legal for promotion.
/// This is true if there are only loads and stores to the alloca... of if there
/// is a PHI node using the address which can be trivially transformed.
///
bool llvm::isAllocaPromotable(const AllocaInst *AI, const TargetData &TD) {
// FIXME: If the memory unit is of pointer or integer type, we can permit
// assignments to subsections of the memory unit.
// Only allow direct loads and stores...
for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
UI != UE; ++UI) // Loop over all of the uses of the alloca
if (isa<LoadInst>(*UI)) {
// noop
} else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
if (SI->getOperand(0) == AI)
return false; // Don't allow a store OF the AI, only INTO the AI.
} else if (const PHINode *PN = dyn_cast<PHINode>(*UI)) {
// We only support PHI nodes in a few simple cases. The PHI node is only
// allowed to have one use, which must be a load instruction, and can only
// use alloca instructions (no random pointers). Also, there cannot be
// any accesses to AI between the PHI node and the use of the PHI.
if (!PN->hasOneUse()) return false;
// Our transformation causes the unconditional loading of all pointer
// operands to the PHI node. Because this could cause a fault if there is
// a critical edge in the CFG and if one of the pointers is illegal, we
// refuse to promote PHI nodes unless they are obviously safe. For now,
// obviously safe means that all of the operands are allocas.
//
// If we wanted to extend this code to break critical edges, this
// restriction could be relaxed, and we could even handle uses of the PHI
// node that are volatile loads or stores.
//
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (!isa<AllocaInst>(PN->getIncomingValue(i)))
return false;
// Now make sure the one user instruction is in the same basic block as
// the PHI, and that there are no loads or stores between the PHI node and
// the access.
BasicBlock::const_iterator UI = cast<Instruction>(PN->use_back());
if (!isa<LoadInst>(UI) || cast<LoadInst>(UI)->isVolatile()) return false;
// Scan looking for memory accesses.
// FIXME: this should REALLY use alias analysis.
for (--UI; !isa<PHINode>(UI); --UI)
if (isa<LoadInst>(UI) || isa<StoreInst>(UI) || isa<CallInst>(UI))
return false;
// If we got this far, we can promote the PHI use.
} else if (const SelectInst *SI = dyn_cast<SelectInst>(*UI)) {
// We only support selects in a few simple cases. The select is only
// allowed to have one use, which must be a load instruction, and can only
// use alloca instructions (no random pointers). Also, there cannot be
// any accesses to AI between the PHI node and the use of the PHI.
if (!SI->hasOneUse()) return false;
// Our transformation causes the unconditional loading of all pointer
// operands of the select. Because this could cause a fault if there is a
// critical edge in the CFG and if one of the pointers is illegal, we
// refuse to promote the select unless it is obviously safe. For now,
// obviously safe means that all of the operands are allocas.
//
if (!isa<AllocaInst>(SI->getOperand(1)) ||
!isa<AllocaInst>(SI->getOperand(2)))
return false;
// Now make sure the one user instruction is in the same basic block as
// the PHI, and that there are no loads or stores between the PHI node and
// the access.
BasicBlock::const_iterator UI = cast<Instruction>(SI->use_back());
if (!isa<LoadInst>(UI) || cast<LoadInst>(UI)->isVolatile()) return false;
// Scan looking for memory accesses.
// FIXME: this should REALLY use alias analysis.
for (--UI; &*UI != SI; --UI)
if (isa<LoadInst>(UI) || isa<StoreInst>(UI) || isa<CallInst>(UI))
return false;
// If we got this far, we can promote the select use.
} else {
return false; // Not a load, store, or promotable PHI?
}
return true;
}
namespace {
struct PromoteMem2Reg {
/// Allocas - The alloca instructions being promoted.
///
std::vector<AllocaInst*> Allocas;
DominatorTree &DT;
DominanceFrontier &DF;
const TargetData &TD;
/// AST - An AliasSetTracker object to update. If null, don't update it.
///
AliasSetTracker *AST;
/// AllocaLookup - Reverse mapping of Allocas.
///
std::map<AllocaInst*, unsigned> AllocaLookup;
/// NewPhiNodes - The PhiNodes we're adding.
///
std::map<BasicBlock*, std::vector<PHINode*> > NewPhiNodes;
/// PointerAllocaValues - If we are updating an AliasSetTracker, then for
/// each alloca that is of pointer type, we keep track of what to copyValue
/// to the inserted PHI nodes here.
///
std::vector<Value*> PointerAllocaValues;
/// Visited - The set of basic blocks the renamer has already visited.
///
std::set<BasicBlock*> Visited;
/// BBNumbers - Contains a stable numbering of basic blocks to avoid
/// non-determinstic behavior.
StableBasicBlockNumbering BBNumbers;
public:
PromoteMem2Reg(const std::vector<AllocaInst*> &A, DominatorTree &dt,
DominanceFrontier &df, const TargetData &td,
AliasSetTracker *ast)
: Allocas(A), DT(dt), DF(df), TD(td), AST(ast) {}
void run();
private:
void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
std::set<PHINode*> &DeadPHINodes);
void PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
void PromoteLocallyUsedAllocas(BasicBlock *BB,
const std::vector<AllocaInst*> &AIs);
void RenamePass(BasicBlock *BB, BasicBlock *Pred,
std::vector<Value*> &IncVals);
bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version,
std::set<PHINode*> &InsertedPHINodes);
};
} // end of anonymous namespace
void PromoteMem2Reg::run() {
Function &F = *DF.getRoot()->getParent();
// LocallyUsedAllocas - Keep track of all of the alloca instructions which are
// only used in a single basic block. These instructions can be efficiently
// promoted by performing a single linear scan over that one block. Since
// individual basic blocks are sometimes large, we group together all allocas
// that are live in a single basic block by the basic block they are live in.
std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas;
if (AST) PointerAllocaValues.resize(Allocas.size());
for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
AllocaInst *AI = Allocas[AllocaNum];
assert(isAllocaPromotable(AI, TD) &&
"Cannot promote non-promotable alloca!");
assert(AI->getParent()->getParent() == &F &&
"All allocas should be in the same function, which is same as DF!");
if (AI->use_empty()) {
// If there are no uses of the alloca, just delete it now.
if (AST) AST->deleteValue(AI);
AI->getParent()->getInstList().erase(AI);
// Remove the alloca from the Allocas list, since it has been processed
Allocas[AllocaNum] = Allocas.back();
Allocas.pop_back();
--AllocaNum;
continue;
}
// Calculate the set of read and write-locations for each alloca. This is
// analogous to finding the 'uses' and 'definitions' of each variable.
std::vector<BasicBlock*> DefiningBlocks;
std::vector<BasicBlock*> UsingBlocks;
BasicBlock *OnlyBlock = 0;
bool OnlyUsedInOneBlock = true;
// As we scan the uses of the alloca instruction, keep track of stores, and
// decide whether all of the loads and stores to the alloca are within the
// same basic block.
RestartUseScan:
Value *AllocaPointerVal = 0;
for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E;++U){
Instruction *User = cast<Instruction>(*U);
if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
// Remember the basic blocks which define new values for the alloca
DefiningBlocks.push_back(SI->getParent());
AllocaPointerVal = SI->getOperand(0);
} else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
// Otherwise it must be a load instruction, keep track of variable reads
UsingBlocks.push_back(LI->getParent());
AllocaPointerVal = LI;
} else if (SelectInst *SI = dyn_cast<SelectInst>(User)) {
// Because of the restrictions we placed on Select instruction uses
// above things are very simple. Transform the select of addresses into
// a select of loaded values.
LoadInst *Load = cast<LoadInst>(SI->use_back());
std::string LoadName = Load->getName(); Load->setName("");
Value *TrueVal = new LoadInst(SI->getOperand(1),
SI->getOperand(1)->getName()+".val", SI);
Value *FalseVal = new LoadInst(SI->getOperand(2),
SI->getOperand(2)->getName()+".val", SI);
Value *NewSI = new SelectInst(SI->getOperand(0), TrueVal,
FalseVal, Load->getName(), SI);
if (AST && isa<PointerType>(Load->getType())) {
AST->copyValue(Load, TrueVal);
AST->copyValue(Load, FalseVal);
AST->copyValue(Load, NewSI);
AST->deleteValue(Load);
}
Load->replaceAllUsesWith(NewSI);
Load->getParent()->getInstList().erase(Load);
SI->getParent()->getInstList().erase(SI);
// Restart our scan of uses...
DefiningBlocks.clear();
UsingBlocks.clear();
goto RestartUseScan;
} else {
// Because of the restrictions we placed on PHI node uses above, the PHI
// node reads the block in any using predecessors. Transform the PHI of
// addresses into a PHI of loaded values.
PHINode *PN = cast<PHINode>(User);
assert(PN->hasOneUse() && "Cannot handle PHI Node with != 1 use!");
LoadInst *PNUser = cast<LoadInst>(PN->use_back());
std::string PNUserName = PNUser->getName(); PNUser->setName("");
// Create the new PHI node and insert load instructions as appropriate.
PHINode *NewPN = new PHINode(AI->getAllocatedType(), PNUserName, PN);
std::map<BasicBlock*, LoadInst*> NewLoads;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *Pred = PN->getIncomingBlock(i);
LoadInst *&NewLoad = NewLoads[Pred];
if (NewLoad == 0) // Insert the new load in the predecessor
NewLoad = new LoadInst(PN->getIncomingValue(i),
PN->getIncomingValue(i)->getName()+".val",
Pred->getTerminator());
NewPN->addIncoming(NewLoad, Pred);
}
if (AST && isa<PointerType>(NewPN->getType())) {
for (std::map<BasicBlock*, LoadInst*>::iterator I = NewLoads.begin(),
E = NewLoads.end(); I != E; ++I)
AST->copyValue(PNUser, I->second);
AST->copyValue(PNUser, NewPN);
AST->deleteValue(PNUser);
AST->deleteValue(PN);
}
// Remove the old load.
PNUser->replaceAllUsesWith(NewPN);
PNUser->getParent()->getInstList().erase(PNUser);
// Remove the old PHI node.
PN->getParent()->getInstList().erase(PN);
// Restart our scan of uses...
DefiningBlocks.clear();
UsingBlocks.clear();
goto RestartUseScan;
}
if (OnlyUsedInOneBlock) {
if (OnlyBlock == 0)
OnlyBlock = User->getParent();
else if (OnlyBlock != User->getParent())
OnlyUsedInOneBlock = false;
}
}
// If the alloca is only read and written in one basic block, just perform a
// linear sweep over the block to eliminate it.
if (OnlyUsedInOneBlock) {
LocallyUsedAllocas[OnlyBlock].push_back(AI);
// Remove the alloca from the Allocas list, since it will be processed.
Allocas[AllocaNum] = Allocas.back();
Allocas.pop_back();
--AllocaNum;
continue;
}
if (AST)
PointerAllocaValues[AllocaNum] = AllocaPointerVal;
// If we haven't computed a numbering for the BB's in the function, do so
// now.
BBNumbers.compute(F);
// Compute the locations where PhiNodes need to be inserted. Look at the
// dominance frontier of EACH basic-block we have a write in.
//
unsigned CurrentVersion = 0;
std::set<PHINode*> InsertedPHINodes;
std::vector<unsigned> DFBlocks;
while (!DefiningBlocks.empty()) {
BasicBlock *BB = DefiningBlocks.back();
DefiningBlocks.pop_back();
// Look up the DF for this write, add it to PhiNodes
DominanceFrontier::const_iterator it = DF.find(BB);
if (it != DF.end()) {
const DominanceFrontier::DomSetType &S = it->second;
// In theory we don't need the indirection through the DFBlocks vector.
// In practice, the order of calling QueuePhiNode would depend on the
// (unspecified) ordering of basic blocks in the dominance frontier,
// which would give PHI nodes non-determinstic subscripts. Fix this by
// processing blocks in order of the occurance in the function.
for (DominanceFrontier::DomSetType::iterator P = S.begin(),PE = S.end();
P != PE; ++P)
DFBlocks.push_back(BBNumbers.getNumber(*P));
// Sort by which the block ordering in the function.
std::sort(DFBlocks.begin(), DFBlocks.end());
for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) {
BasicBlock *BB = BBNumbers.getBlock(DFBlocks[i]);
if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes))
DefiningBlocks.push_back(BB);
}
DFBlocks.clear();
}
}
// Now that we have inserted PHI nodes along the Iterated Dominance Frontier
// of the writes to the variable, scan through the reads of the variable,
// marking PHI nodes which are actually necessary as alive (by removing them
// from the InsertedPHINodes set). This is not perfect: there may PHI
// marked alive because of loads which are dominated by stores, but there
// will be no unmarked PHI nodes which are actually used.
//
for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i)
MarkDominatingPHILive(UsingBlocks[i], AllocaNum, InsertedPHINodes);
UsingBlocks.clear();
// If there are any PHI nodes which are now known to be dead, remove them!
for (std::set<PHINode*>::iterator I = InsertedPHINodes.begin(),
E = InsertedPHINodes.end(); I != E; ++I) {
PHINode *PN = *I;
std::vector<PHINode*> &BBPNs = NewPhiNodes[PN->getParent()];
BBPNs[AllocaNum] = 0;
// Check to see if we just removed the last inserted PHI node from this
// basic block. If so, remove the entry for the basic block.
bool HasOtherPHIs = false;
for (unsigned i = 0, e = BBPNs.size(); i != e; ++i)
if (BBPNs[i]) {
HasOtherPHIs = true;
break;
}
if (!HasOtherPHIs)
NewPhiNodes.erase(PN->getParent());
if (AST && isa<PointerType>(PN->getType()))
AST->deleteValue(PN);
PN->getParent()->getInstList().erase(PN);
}
// Keep the reverse mapping of the 'Allocas' array.
AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
}
// Process all allocas which are only used in a single basic block.
for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I =
LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){
const std::vector<AllocaInst*> &Allocas = I->second;
assert(!Allocas.empty() && "empty alloca list??");
// It's common for there to only be one alloca in the list. Handle it
// efficiently.
if (Allocas.size() == 1)
PromoteLocallyUsedAlloca(I->first, Allocas[0]);
else
PromoteLocallyUsedAllocas(I->first, Allocas);
}
if (Allocas.empty())
return; // All of the allocas must have been trivial!
// Set the incoming values for the basic block to be null values for all of
// the alloca's. We do this in case there is a load of a value that has not
// been stored yet. In this case, it will get this null value.
//
std::vector<Value *> Values(Allocas.size());
for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
Values[i] = Constant::getNullValue(Allocas[i]->getAllocatedType());
// Walks all basic blocks in the function performing the SSA rename algorithm
// and inserting the phi nodes we marked as necessary
//
RenamePass(F.begin(), 0, Values);
// The renamer uses the Visited set to avoid infinite loops. Clear it now.
Visited.clear();
// Remove the allocas themselves from the function...
for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
Instruction *A = Allocas[i];
// If there are any uses of the alloca instructions left, they must be in
// sections of dead code that were not processed on the dominance frontier.
// Just delete the users now.
//
if (!A->use_empty())
A->replaceAllUsesWith(Constant::getNullValue(A->getType()));
if (AST) AST->deleteValue(A);
A->getParent()->getInstList().erase(A);
}
// At this point, the renamer has added entries to PHI nodes for all reachable
// code. Unfortunately, there may be blocks which are not reachable, which
// the renamer hasn't traversed. If this is the case, the PHI nodes may not
// have incoming values for all predecessors. Loop over all PHI nodes we have
// created, inserting null constants if they are missing any incoming values.
//
for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I =
NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first));
std::vector<PHINode*> &PNs = I->second;
assert(!PNs.empty() && "Empty PHI node list??");
// Only do work here if there the PHI nodes are missing incoming values. We
// know that all PHI nodes that were inserted in a block will have the same
// number of incoming values, so we can just check any PHI node.
PHINode *FirstPHI;
for (unsigned i = 0; (FirstPHI = PNs[i]) == 0; ++i)
/*empty*/;
if (Preds.size() != FirstPHI->getNumIncomingValues()) {
// Ok, now we know that all of the PHI nodes are missing entries for some
// basic blocks. Start by sorting the incoming predecessors for efficient
// access.
std::sort(Preds.begin(), Preds.end());
// Now we loop through all BB's which have entries in FirstPHI and remove
// them from the Preds list.
for (unsigned i = 0, e = FirstPHI->getNumIncomingValues(); i != e; ++i) {
// Do a log(n) search of the Preds list for the entry we want.
std::vector<BasicBlock*>::iterator EntIt =
std::lower_bound(Preds.begin(), Preds.end(),
FirstPHI->getIncomingBlock(i));
assert(EntIt != Preds.end() && *EntIt == FirstPHI->getIncomingBlock(i)&&
"PHI node has entry for a block which is not a predecessor!");
// Remove the entry
Preds.erase(EntIt);
}
// At this point, the blocks left in the preds list must have dummy
// entries inserted into every PHI nodes for the block.
for (unsigned i = 0, e = PNs.size(); i != e; ++i)
if (PHINode *PN = PNs[i]) {
Value *NullVal = Constant::getNullValue(PN->getType());
for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred)
PN->addIncoming(NullVal, Preds[pred]);
}
}
}
}
// MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not
// "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF
// as usual (inserting the PHI nodes in the DeadPHINodes set), then processes
// each read of the variable. For each block that reads the variable, this
// function is called, which removes used PHI nodes from the DeadPHINodes set.
// After all of the reads have been processed, any PHI nodes left in the
// DeadPHINodes set are removed.
//
void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
std::set<PHINode*> &DeadPHINodes) {
// Scan the immediate dominators of this block looking for a block which has a
// PHI node for Alloca num. If we find it, mark the PHI node as being alive!
for (DominatorTree::Node *N = DT[BB]; N; N = N->getIDom()) {
BasicBlock *DomBB = N->getBlock();
std::map<BasicBlock*, std::vector<PHINode*> >::iterator
I = NewPhiNodes.find(DomBB);
if (I != NewPhiNodes.end() && I->second[AllocaNum]) {
// Ok, we found an inserted PHI node which dominates this value.
PHINode *DominatingPHI = I->second[AllocaNum];
// Find out if we previously thought it was dead.
std::set<PHINode*>::iterator DPNI = DeadPHINodes.find(DominatingPHI);
if (DPNI != DeadPHINodes.end()) {
// Ok, until now, we thought this PHI node was dead. Mark it as being
// alive/needed.
DeadPHINodes.erase(DPNI);
// Now that we have marked the PHI node alive, also mark any PHI nodes
// which it might use as being alive as well.
for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB);
PI != PE; ++PI)
MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes);
}
}
}
}
/// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic
/// block. If this is the case, avoid traversing the CFG and inserting a lot of
/// potentially useless PHI nodes by just performing a single linear pass over
/// the basic block using the Alloca.
///
void PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
assert(!AI->use_empty() && "There are no uses of the alloca!");
// Handle degenerate cases quickly.
if (AI->hasOneUse()) {
Instruction *U = cast<Instruction>(AI->use_back());
if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
// Must be a load of uninitialized value.
LI->replaceAllUsesWith(Constant::getNullValue(AI->getAllocatedType()));
if (AST && isa<PointerType>(LI->getType()))
AST->deleteValue(LI);
} else {
// Otherwise it must be a store which is never read.
assert(isa<StoreInst>(U));
}
BB->getInstList().erase(U);
} else {
// Uses of the uninitialized memory location shall get zero...
Value *CurVal = Constant::getNullValue(AI->getAllocatedType());
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
Instruction *Inst = I++;
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
if (LI->getOperand(0) == AI) {
// Loads just returns the "current value"...
LI->replaceAllUsesWith(CurVal);
if (AST && isa<PointerType>(LI->getType()))
AST->deleteValue(LI);
BB->getInstList().erase(LI);
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (SI->getOperand(1) == AI) {
// Store updates the "current value"...
CurVal = SI->getOperand(0);
BB->getInstList().erase(SI);
}
}
}
}
// After traversing the basic block, there should be no more uses of the
// alloca, remove it now.
assert(AI->use_empty() && "Uses of alloca from more than one BB??");
if (AST) AST->deleteValue(AI);
AI->getParent()->getInstList().erase(AI);
}
/// PromoteLocallyUsedAllocas - This method is just like
/// PromoteLocallyUsedAlloca, except that it processes multiple alloca
/// instructions in parallel. This is important in cases where we have large
/// basic blocks, as we don't want to rescan the entire basic block for each
/// alloca which is locally used in it (which might be a lot).
void PromoteMem2Reg::
PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) {
std::map<AllocaInst*, Value*> CurValues;
for (unsigned i = 0, e = AIs.size(); i != e; ++i)
CurValues[AIs[i]] = 0; // Insert with null value
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
Instruction *Inst = I++;
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
// Is this a load of an alloca we are tracking?
if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) {
std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
if (AIt != CurValues.end()) {
// Loads just returns the "current value"...
if (AIt->second == 0) // Uninitialized value??
AIt->second =Constant::getNullValue(AIt->first->getAllocatedType());
LI->replaceAllUsesWith(AIt->second);
if (AST && isa<PointerType>(LI->getType()))
AST->deleteValue(LI);
BB->getInstList().erase(LI);
}
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) {
std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
if (AIt != CurValues.end()) {
// Store updates the "current value"...
AIt->second = SI->getOperand(0);
BB->getInstList().erase(SI);
}
}
}
}
}
// QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
// Alloca returns true if there wasn't already a phi-node for that variable
//
bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
unsigned &Version,
std::set<PHINode*> &InsertedPHINodes) {
// Look up the basic-block in question.
std::vector<PHINode*> &BBPNs = NewPhiNodes[BB];
if (BBPNs.empty()) BBPNs.resize(Allocas.size());
// If the BB already has a phi node added for the i'th alloca then we're done!
if (BBPNs[AllocaNo]) return false;
// Create a PhiNode using the dereferenced type... and add the phi-node to the
// BasicBlock.
PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
Allocas[AllocaNo]->getName() + "." +
utostr(Version++), BB->begin());
BBPNs[AllocaNo] = PN;
InsertedPHINodes.insert(PN);
if (AST && isa<PointerType>(PN->getType()))
AST->copyValue(PointerAllocaValues[AllocaNo], PN);
return true;
}
// RenamePass - Recursively traverse the CFG of the function, renaming loads and
// stores to the allocas which we are promoting. IncomingVals indicates what
// value each Alloca contains on exit from the predecessor block Pred.
//
void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
std::vector<Value*> &IncomingVals) {
// If this BB needs a PHI node, update the PHI node for each variable we need
// PHI nodes for.
std::map<BasicBlock*, std::vector<PHINode *> >::iterator
BBPNI = NewPhiNodes.find(BB);
if (BBPNI != NewPhiNodes.end()) {
std::vector<PHINode *> &BBPNs = BBPNI->second;
for (unsigned k = 0; k != BBPNs.size(); ++k)
if (PHINode *PN = BBPNs[k]) {
// Add this incoming value to the PHI node.
PN->addIncoming(IncomingVals[k], Pred);
// The currently active variable for this block is now the PHI.
IncomingVals[k] = PN;
}
}
// don't revisit nodes
if (Visited.count(BB)) return;
// mark as visited
Visited.insert(BB);
for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) {
Instruction *I = II++; // get the instruction, increment iterator
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) {
std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src);
if (AI != AllocaLookup.end()) {
Value *V = IncomingVals[AI->second];
// walk the use list of this load and replace all uses with r
LI->replaceAllUsesWith(V);
if (AST && isa<PointerType>(LI->getType()))
AST->deleteValue(LI);
BB->getInstList().erase(LI);
}
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
// Delete this instruction and mark the name as the current holder of the
// value
if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) {
std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
if (ai != AllocaLookup.end()) {
// what value were we writing?
IncomingVals[ai->second] = SI->getOperand(0);
BB->getInstList().erase(SI);
}
}
}
}
// Recurse to our successors.
TerminatorInst *TI = BB->getTerminator();
for (unsigned i = 0; i != TI->getNumSuccessors(); i++) {
std::vector<Value*> OutgoingVals(IncomingVals);
RenamePass(TI->getSuccessor(i), BB, OutgoingVals);
}
}
/// PromoteMemToReg - Promote the specified list of alloca instructions into
/// scalar registers, inserting PHI nodes as appropriate. This function makes
/// use of DominanceFrontier information. This function does not modify the CFG
/// of the function at all. All allocas must be from the same function.
///
/// If AST is specified, the specified tracker is updated to reflect changes
/// made to the IR.
///
void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
DominatorTree &DT, DominanceFrontier &DF,
const TargetData &TD, AliasSetTracker *AST) {
// If there is nothing to do, bail out...
if (Allocas.empty()) return;
PromoteMem2Reg(Allocas, DT, DF, TD, AST).run();
}