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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10727 91177308-0d34-0410-b5e6-96231b3b80d8
164 lines
6.4 KiB
C++
164 lines
6.4 KiB
C++
//===- DemoteRegToStack.cpp - Move a virtual register to the stack --------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file provide the function DemoteRegToStack(). This function takes a
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// virtual register computed by an Instruction& X and replaces it with a slot in
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// the stack frame, allocated via alloca. It returns the pointer to the
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// AllocaInst inserted.
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//
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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/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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using namespace llvm;
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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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static inline void PushOperandsOnWorkList(std::vector<Instruction*>& workList,
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PhiSet& phisToGo, PHINode* phiN) {
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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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Instruction* opI = cast<Instruction>(OI);
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if (!isa<PHINode>(opI) || !phisToGo.count(cast<PHINode>(opI)))
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workList.push_back(opI);
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}
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}
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static void FindPhis(Instruction& X, PhiSet& phisToGo) {
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std::vector<Instruction*> workList;
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workList.push_back(&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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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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while (!workList.empty()) {
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Instruction *I = workList.back();
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workList.pop_back();
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for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++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_back(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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// 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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static void LoadBeforeUses(Instruction* def, AllocaInst* XSlot) {
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for (unsigned nPhis = 0; def->use_size() - nPhis > 0; ) {
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Instruction* useI = cast<Instruction>(def->use_back());
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if (!isa<PHINode>(useI)) {
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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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} else
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++nPhis;
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}
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}
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static void AddLoadsAndStores(AllocaInst* XSlot, Instruction& X,
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PhiSet& phisToGo) {
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for (PhiSetIterator PI=phisToGo.begin(), PE=phisToGo.end(); PI != PE; ++PI) {
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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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Value* phiOp = pn->getIncomingValue(i);
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if (phiOp != &X &&
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(!isa<PHINode>(phiOp) || !phisToGo.count(cast<PHINode>(phiOp)))) {
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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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} 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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//----------------------------------------------------------------------------
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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* llvm::DemoteRegToStack(Instruction& X) {
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if (X.getType() == Type::VoidTy)
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return 0; // 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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Function* parentFunc = X.getParent()->getParent();
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AllocaInst *XSlot = new AllocaInst(X.getType(), 0, X.getName(),
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parentFunc->getEntryBlock().begin());
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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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for (PhiSetIterator PI = phisToGo.begin(), E = phisToGo.end(); PI != E; ++PI)
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(*PI)->getParent()->getInstList().erase(*PI);
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return XSlot;
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}
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