//===- 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 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
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
+#include "llvm/Type.h"
+#include <map>
using namespace llvm;
/// DemoteRegToStack - This function takes a virtual register computed by an
/// 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 0;
+ }
+
// 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(), 0,
+ I.getName()+".reg2mem", AllocaPoint);
+ } else {
+ Function *F = I.getParent()->getParent();
+ Slot = new AllocaInst(I.getType(), 0, I.getName()+".reg2mem",
+ F->getEntryBlock().begin());
+ }
+
// Change all of the users of the instruction to read from the stack slot
// instead.
while (!I.use_empty()) {
// 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 multiple loads. The problem is that the resultant
+ // 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
+ // and reuse loads we insert.
+ std::map<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 == 0) {
+ // 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.
+ 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;
+ ++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!");
+ // We cannot demote invoke instructions to the stack if their normal edge
+ // is critical.
+ InvokeInst &II = cast<InvokeInst>(I);
+ assert(II.getNormalDest()->getSinglePredecessor() &&
+ "Cannot demote invoke with a critical successor!");
+ InsertPt = II.getNormalDest()->begin();
+ }
+
+ for (; isa<PHINode>(InsertPt); ++InsertPt)
+ /* empty */; // Don't insert before any PHI nodes.
+ 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 and it returns the pointer to the alloca inserted.
+AllocaInst* llvm::DemotePHIToStack(PHINode *P, Instruction *AllocaPoint) {
+ if (P->use_empty()) {
+ P->eraseFromParent();
+ return 0;
}
+ // Create a stack slot to hold the value.
+ AllocaInst *Slot;
+ if (AllocaPoint) {
+ Slot = new AllocaInst(P->getType(), 0,
+ P->getName()+".reg2mem", AllocaPoint);
+ } else {
+ Function *F = P->getParent()->getParent();
+ Slot = new AllocaInst(P->getType(), 0, P->getName()+".reg2mem",
+ F->getEntryBlock().begin());
+ }
+
+ // Iterate over each operand, insert 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"); II=II;
+ }
+ new StoreInst(P->getIncomingValue(i), Slot,
+ P->getIncomingBlock(i)->getTerminator());
+ }
+
+ // Insert load in place of the phi and replace all uses.
+ Value *V = new LoadInst(Slot, P->getName()+".reload", P);
+ P->replaceAllUsesWith(V);
+
+ // Delete phi.
+ P->eraseFromParent();
+
return Slot;
}
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