| //===- DemoteRegToStack.cpp - Move a virtual register to the stack --------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file provide the function DemoteRegToStack(). This function takes a |
| // virtual register computed by an Instruction and replaces it with a slot in |
| // the stack frame, allocated via alloca. It returns the pointer to the |
| // AllocaInst inserted. After this function is called on an instruction, we are |
| // guaranteed that the only user of the instruction is a store that is |
| // immediately after it. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Function.h" |
| #include "llvm/Instructions.h" |
| using namespace llvm; |
| |
| /// DemoteRegToStack - This function takes a virtual register computed by an |
| /// Instruction and replaces it with a slot in the stack frame, allocated via |
| /// alloca. This allows the CFG to be changed around without fear of |
| /// invalidating the SSA information for the value. It returns the pointer to |
| /// the alloca inserted to create a stack slot for I. |
| /// |
| AllocaInst* llvm::DemoteRegToStack(Instruction &I) { |
| if (I.use_empty()) return 0; // nothing to do! |
| |
| // Create a stack slot to hold the value. |
| Function *F = I.getParent()->getParent(); |
| AllocaInst *Slot = new AllocaInst(I.getType(), 0, I.getName(), |
| F->getEntryBlock().begin()); |
| |
| // Change all of the users of the instruction to read from the stack slot |
| // instead. |
| while (!I.use_empty()) { |
| Instruction *U = cast<Instruction>(I.use_back()); |
| if (PHINode *PN = dyn_cast<PHINode>(U)) { |
| // If this is a PHI node, we can't insert a load of the value before the |
| // use. Instead, insert the load in the predecessor block corresponding |
| // to the incoming value. |
| // |
| // Note that if there are multiple edges from a basic block to this PHI |
| // node that we'll insert multiple loads. Since DemoteRegToStack requires |
| // a mem2reg pass after it (to produce reasonable code), we don't care. |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) |
| if (PN->getIncomingValue(i) == &I) { |
| // Insert the load into the predecessor block |
| Value *V = new LoadInst(Slot, I.getName()+".reload", |
| PN->getIncomingBlock(i)->getTerminator()); |
| PN->setIncomingValue(i, V); |
| } |
| |
| } else { |
| // If this is a normal instruction, just insert a load. |
| Value *V = new LoadInst(Slot, I.getName()+".reload", U); |
| U->replaceUsesOfWith(&I, V); |
| } |
| } |
| |
| |
| // Insert stores of the computed value into the stack slot. We have to be |
| // careful is I is an invoke instruction though, because we can't insert the |
| // store AFTER the terminator instruction. |
| if (!isa<TerminatorInst>(I)) { |
| BasicBlock::iterator InsertPt = &I; |
| for (++InsertPt; isa<PHINode>(InsertPt); ++InsertPt) |
| /* empty */; // Don't insert before any PHI nodes. |
| new StoreInst(&I, Slot, InsertPt); |
| } else { |
| // FIXME: We cannot yet demote invoke instructions to the stack, because |
| // doing so would require breaking critical edges. This should be fixed |
| // eventually. |
| assert(0 && |
| "Cannot demote the value computed by an invoke instruction yet!"); |
| } |
| |
| return Slot; |
| } |