llvm/lib/Transforms/Utils/DemoteRegToStack.cpp
2003-05-29 15:12:27 +00:00

192 lines
7.0 KiB
C++

//===- DemoteRegToStack.cpp - Move a virtual reg. to stack ------*- C++ -*-===//
//
// This file provide the function DemoteRegToStack(). This function takes a
// virtual register computed by an Instruction& X and replaces it with a slot in
// the stack frame, allocated via alloca. It returns the pointer to the
// AllocaInst inserted.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/DemoteRegToStack.h"
#include "llvm/Function.h"
#include "llvm/iMemory.h"
#include "llvm/iPHINode.h"
#include "llvm/iTerminators.h"
#include "llvm/Type.h"
#include "Support/hash_set"
#include <stack>
//----------------------------------------------------------------------------
// function DemoteRegToStack()
//
//----------------------------------------------------------------------------
typedef hash_set<PHINode*> PhiSet;
typedef hash_set<PHINode*>::iterator PhiSetIterator;
// Helper function to push a phi *and* all its operands to the worklist!
// Do not push an instruction if it is already in the result set of Phis to go.
inline void PushOperandsOnWorkList(std::stack<Instruction*>& workList,
PhiSet& phisToGo, PHINode* phiN) {
for (User::op_iterator OI = phiN->op_begin(), OE = phiN->op_end();
OI != OE; ++OI)
if (Instruction* opI = dyn_cast<Instruction>(OI))
if (!isa<PHINode>(opI) ||
phisToGo.find(cast<PHINode>(opI)) == phisToGo.end())
workList.push(opI);
}
void FindPhis(Instruction& X, PhiSet& phisToGo)
{
std::stack<Instruction*> workList;
workList.push(&X);
// Handle the case that X itself is a Phi!
if (PHINode* phiX = dyn_cast<PHINode>(&X))
{
phisToGo.insert(phiX);
PushOperandsOnWorkList(workList, phisToGo, phiX);
}
// Now use a worklist to find all phis reachable from X, and
// (recursively) all phis reachable from operands of such phis.
for (Instruction* workI; !workList.empty(); workList.pop())
{
workI = workList.top();
for (Value::use_iterator UI=workI->use_begin(), UE=workI->use_end();
UI != UE; ++UI)
if (PHINode* phiN = dyn_cast<PHINode>(*UI))
if (phisToGo.find(phiN) == phisToGo.end())
{ // Seeing this phi for the first time: it must go!
phisToGo.insert(phiN);
workList.push(phiN);
PushOperandsOnWorkList(workList, phisToGo, phiN);
}
}
}
// Create the Alloca for X
AllocaInst* CreateAllocaForX(Instruction& X)
{
Function* parentFunc = X.getParent()->getParent();
Instruction* entryInst = parentFunc->getEntryNode().begin();
return new AllocaInst(X.getType(), /*arraySize*/ NULL,
X.hasName()? X.getName()+std::string("OnStack")
: "DemotedTmp",
entryInst);
}
// Insert loads before all uses of I, except uses in Phis
// since all such Phis *must* be deleted.
void LoadBeforeUses(Instruction* def, AllocaInst* XSlot)
{
for (unsigned nPhis = 0; def->use_size() - nPhis > 0; )
{
Instruction* useI = cast<Instruction>(def->use_back());
if (!isa<PHINode>(useI))
{
LoadInst* loadI =
new LoadInst(XSlot, std::string("Load")+XSlot->getName(), useI);
useI->replaceUsesOfWith(def, loadI);
}
else
++nPhis;
}
}
void AddLoadsAndStores(AllocaInst* XSlot, Instruction& X, PhiSet& phisToGo)
{
for (PhiSetIterator PI=phisToGo.begin(), PE=phisToGo.end(); PI != PE; ++PI)
{
PHINode* pn = *PI;
// First, insert loads before all uses except uses in Phis.
// Do this first because new stores will appear as uses also!
LoadBeforeUses(pn, XSlot);
// For every incoming operand of the Phi, insert a store either
// just after the instruction defining the value or just before the
// predecessor of the Phi if the value is a formal, not an instruction.
//
for (unsigned i=0, N=pn->getNumIncomingValues(); i < N; ++i)
{
Value* phiOp = pn->getIncomingValue(i);
if (phiOp != &X &&
(!isa<PHINode>(phiOp) ||
phisToGo.find(cast<PHINode>(phiOp)) == phisToGo.end()))
{ // This operand is not a phi that will be deleted: need to store.
assert(!isa<TerminatorInst>(phiOp));
Instruction* storeBefore;
if (Instruction* I = dyn_cast<Instruction>(phiOp))
{ // phiOp is an instruction, store its result right after it.
assert(I->getNext() && "Non-terminator without successor?");
storeBefore = I->getNext();
}
else
{ // If not, it must be a formal: store it at the end of the
// predecessor block of the Phi (*not* at function entry!).
storeBefore = pn->getIncomingBlock(i)->getTerminator();
}
// Create instr. to store the value of phiOp before `insertBefore'
StoreInst* storeI = new StoreInst(phiOp, XSlot, storeBefore);
}
}
}
}
void DeletePhis(PhiSet& phisToGo)
{
for (PhiSetIterator PI=phisToGo.begin(), PE=phisToGo.end(); PI != PE; ++PI)
{
assert((*PI)->use_size() == 0 && "This PHI should be DEAD!");
(*PI)->getParent()->getInstList().remove(*PI);
delete *PI;
}
phisToGo.clear();
}
//----------------------------------------------------------------------------
// function DemoteRegToStack()
//
// This function takes a virtual register computed by an
// Instruction& X and replaces it with a slot in the stack frame,
// allocated via alloca. It has to:
// (1) Identify all Phi operations that have X as an operand and
// transitively other Phis that use such Phis;
// (2) Store all values merged with X via Phi operations to the stack slot;
// (3) Load the value from the stack slot just before any use of X or any
// of the Phis that were eliminated; and
// (4) Delete all the Phis, which should all now be dead.
//
// Returns the pointer to the alloca inserted to create a stack slot for X.
//----------------------------------------------------------------------------
AllocaInst* DemoteRegToStack(Instruction& X)
{
if (X.getType() == Type::VoidTy)
return NULL; // nothing to do!
// Find all Phis involving X or recursively using such Phis or Phis
// involving operands of such Phis (essentially all Phis in the "web" of X)
PhiSet phisToGo;
FindPhis(X, phisToGo);
// Create a stack slot to hold X
AllocaInst* XSlot = CreateAllocaForX(X);
// Insert loads before all uses of X and (*only then*) insert store after X
assert(X.getNext() && "Non-terminator (since non-void) with no successor?");
LoadBeforeUses(&X, XSlot);
StoreInst* storeI = new StoreInst(&X, XSlot, X.getNext());
// Do the same for all the phis that will be deleted
AddLoadsAndStores(XSlot, X, phisToGo);
// Delete the phis and return the alloca instruction
DeletePhis(phisToGo);
return XSlot;
}