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This code was both incredibly complex and incredibly broken. Fix it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12456 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
parent
df22f9c41b
commit
c1a0623e86
@ -8,156 +8,76 @@
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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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// virtual register computed by an Instruction 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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// AllocaInst inserted. After this function is called on an instruction, we are
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// guaranteed that the only user of the instruction is a store that is
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// immediately after it.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/Local.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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#include "llvm/Instructions.h"
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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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/// DemoteRegToStack - This function takes a virtual register computed by an
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/// Instruction and replaces it with a slot in the stack frame, allocated via
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/// alloca. This allows the CFG to be changed around without fear of
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/// invalidating the SSA information for the value. It returns the pointer to
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/// the alloca inserted to create a stack slot for I.
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///
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AllocaInst* llvm::DemoteRegToStack(Instruction &I) {
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if (I.use_empty()) return 0; // nothing to do!
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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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// Create a stack slot to hold the value.
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Function *F = I.getParent()->getParent();
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AllocaInst *Slot = new AllocaInst(I.getType(), 0, I.getName(),
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F->getEntryBlock().begin());
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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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// Change all of the users of the instruction to read from the stack slot
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// instead.
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while (!I.use_empty()) {
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Instruction *U = cast<Instruction>(I.use_back());
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if (PHINode *PN = dyn_cast<PHINode>(U)) {
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// If this is a PHI node, we can't insert a load of the value before the
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// use. Instead, insert the load in the predecessor block corresponding
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// to the incoming value.
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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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// Note that if there are multiple edges from a basic block to this PHI
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// node that we'll insert multiple loads. Since DemoteRegToStack requires
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// a mem2reg pass after it (to produce reasonable code), we don't care.
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
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if (PN->getIncomingValue(i) == &I) {
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// Insert the load into the predecessor block
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Value *V = new LoadInst(Slot, I.getName()+".reload",
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PN->getIncomingBlock(i)->getTerminator());
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PN->setIncomingValue(i, V);
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}
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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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// If this is a normal instruction, just insert a load.
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Value *V = new LoadInst(Slot, I.getName()+".reload", U);
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U->replaceUsesOfWith(&I, V);
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}
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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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// Insert stores of the computed value into the stack slot. We have to be
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// careful is I is an invoke instruction though, because we can't insert the
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// store AFTER the terminator instruction.
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if (!isa<TerminatorInst>(I)) {
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BasicBlock::iterator InsertPt = &I;
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for (++InsertPt; isa<PHINode>(InsertPt); ++InsertPt)
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/* empty */; // Don't insert before any PHI nodes.
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new StoreInst(&I, Slot, InsertPt);
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} else {
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// FIXME: We cannot yet demote invoke instructions to the stack, because
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// doing so would require breaking critical edges. This should be fixed
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// eventually.
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assert(0 &&
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"Cannot demote the value computed by an invoke instruction yet!");
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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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return Slot;
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}
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