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