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