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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207196 91177308-0d34-0410-b5e6-96231b3b80d8
150 lines
5.8 KiB
C++
150 lines
5.8 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 is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/Analysis/CFG.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Type.h"
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#include "llvm/Transforms/Utils/Local.h"
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using namespace llvm;
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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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AllocaInst *llvm::DemoteRegToStack(Instruction &I, bool VolatileLoads,
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Instruction *AllocaPoint) {
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if (I.use_empty()) {
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I.eraseFromParent();
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return nullptr;
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}
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// Create a stack slot to hold the value.
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AllocaInst *Slot;
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if (AllocaPoint) {
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Slot = new AllocaInst(I.getType(), nullptr,
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I.getName()+".reg2mem", AllocaPoint);
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} else {
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Function *F = I.getParent()->getParent();
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Slot = new AllocaInst(I.getType(), nullptr, I.getName()+".reg2mem",
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F->getEntryBlock().begin());
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}
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// Change all of the users of the instruction to read from the stack slot.
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while (!I.use_empty()) {
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Instruction *U = cast<Instruction>(I.user_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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// Note that if there are multiple edges from a basic block to this PHI
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// node that we cannot have multiple loads. The problem is that the
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// resulting PHI node will have multiple values (from each load) coming in
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// from the same block, which is illegal SSA form. For this reason, we
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// keep track of and reuse loads we insert.
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DenseMap<BasicBlock*, Value*> Loads;
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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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Value *&V = Loads[PN->getIncomingBlock(i)];
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if (!V) {
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// Insert the load into the predecessor block
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V = new LoadInst(Slot, I.getName()+".reload", VolatileLoads,
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PN->getIncomingBlock(i)->getTerminator());
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}
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PN->setIncomingValue(i, V);
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}
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} else {
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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", VolatileLoads, U);
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U->replaceUsesOfWith(&I, V);
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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 if I is an invoke instruction, because we can't insert the store
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// AFTER the terminator instruction.
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BasicBlock::iterator InsertPt;
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if (!isa<TerminatorInst>(I)) {
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InsertPt = &I;
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++InsertPt;
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} else {
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InvokeInst &II = cast<InvokeInst>(I);
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if (II.getNormalDest()->getSinglePredecessor())
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InsertPt = II.getNormalDest()->getFirstInsertionPt();
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else {
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// We cannot demote invoke instructions to the stack if their normal edge
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// is critical. Therefore, split the critical edge and insert the store
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// in the newly created basic block.
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unsigned SuccNum = GetSuccessorNumber(I.getParent(), II.getNormalDest());
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TerminatorInst *TI = &cast<TerminatorInst>(I);
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assert (isCriticalEdge(TI, SuccNum) &&
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"Expected a critical edge!");
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BasicBlock *BB = SplitCriticalEdge(TI, SuccNum);
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assert (BB && "Unable to split critical edge.");
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InsertPt = BB->getFirstInsertionPt();
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}
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}
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for (; isa<PHINode>(InsertPt) || isa<LandingPadInst>(InsertPt); ++InsertPt)
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/* empty */; // Don't insert before PHI nodes or landingpad instrs.
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new StoreInst(&I, Slot, InsertPt);
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return Slot;
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}
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/// DemotePHIToStack - This function takes a virtual register computed by a PHI
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/// node and replaces it with a slot in the stack frame allocated via alloca.
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/// The PHI node is deleted. It returns the pointer to the alloca inserted.
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AllocaInst *llvm::DemotePHIToStack(PHINode *P, Instruction *AllocaPoint) {
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if (P->use_empty()) {
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P->eraseFromParent();
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return nullptr;
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}
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// Create a stack slot to hold the value.
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AllocaInst *Slot;
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if (AllocaPoint) {
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Slot = new AllocaInst(P->getType(), nullptr,
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P->getName()+".reg2mem", AllocaPoint);
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} else {
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Function *F = P->getParent()->getParent();
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Slot = new AllocaInst(P->getType(), nullptr, P->getName()+".reg2mem",
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F->getEntryBlock().begin());
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}
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// Iterate over each operand inserting a store in each predecessor.
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for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
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if (InvokeInst *II = dyn_cast<InvokeInst>(P->getIncomingValue(i))) {
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assert(II->getParent() != P->getIncomingBlock(i) &&
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"Invoke edge not supported yet"); (void)II;
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}
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new StoreInst(P->getIncomingValue(i), Slot,
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P->getIncomingBlock(i)->getTerminator());
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}
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// Insert a load in place of the PHI and replace all uses.
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BasicBlock::iterator InsertPt = P;
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for (; isa<PHINode>(InsertPt) || isa<LandingPadInst>(InsertPt); ++InsertPt)
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/* empty */; // Don't insert before PHI nodes or landingpad instrs.
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Value *V = new LoadInst(Slot, P->getName()+".reload", InsertPt);
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P->replaceAllUsesWith(V);
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// Delete PHI.
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P->eraseFromParent();
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return Slot;
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}
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