/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the
/// old header into the preheader. If there were uses of the values produced by
/// these instruction that were outside of the loop, we have to insert PHI nodes
/// to merge the two values. Do this now.
static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
BasicBlock *OrigPreheader,
ValueToValueMapTy &ValueMap) {
// Remove PHI node entries that are no longer live.
BasicBlock::iterator I, E = OrigHeader->end();
for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreheader));
// Now fix up users of the instructions in OrigHeader, inserting PHI nodes
// as necessary.
SSAUpdater SSA;
for (I = OrigHeader->begin(); I != E; ++I) {
Value *OrigHeaderVal = &*I;
// If there are no uses of the value (e.g. because it returns void), there
// is nothing to rewrite.
if (OrigHeaderVal->use_empty())
continue;
Value *OrigPreHeaderVal = ValueMap.lookup(OrigHeaderVal);
// The value now exits in two versions: the initial value in the preheader
// and the loop "next" value in the original header.
SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName());
SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
SSA.AddAvailableValue(OrigPreheader, OrigPreHeaderVal);
// Visit each use of the OrigHeader instruction.
for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
UE = OrigHeaderVal->use_end(); UI != UE; ) {
// Grab the use before incrementing the iterator.
Use &U = *UI;
// Increment the iterator before removing the use from the list.
++UI;
// SSAUpdater can't handle a non-PHI use in the same block as an
// earlier def. We can easily handle those cases manually.
Instruction *UserInst = cast<Instruction>(U.getUser());
if (!isa<PHINode>(UserInst)) {
BasicBlock *UserBB = UserInst->getParent();
// The original users in the OrigHeader are already using the
// original definitions.
if (UserBB == OrigHeader)
continue;
// Users in the OrigPreHeader need to use the value to which the
// original definitions are mapped.
if (UserBB == OrigPreheader) {
U = OrigPreHeaderVal;
continue;
}
}
// Anything else can be handled by SSAUpdater.
SSA.RewriteUse(U);
}
// Replace MetadataAsValue(ValueAsMetadata(OrigHeaderVal)) uses in debug
// intrinsics.
LLVMContext &C = OrigHeader->getContext();
if (auto *VAM = ValueAsMetadata::getIfExists(OrigHeaderVal)) {
if (auto *MAV = MetadataAsValue::getIfExists(C, VAM)) {
for (auto UI = MAV->use_begin(), E = MAV->use_end(); UI != E; ) {
// Grab the use before incrementing the iterator. Otherwise, altering
// the Use will invalidate the iterator.
Use &U = *UI++;
DbgInfoIntrinsic *UserInst = dyn_cast<DbgInfoIntrinsic>(U.getUser());
if (!UserInst) continue;
// The original users in the OrigHeader are already using the original
// definitions.
BasicBlock *UserBB = UserInst->getParent();
if (UserBB == OrigHeader)
continue;
// Users in the OrigPreHeader need to use the value to which the
// original definitions are mapped and anything else can be handled by
// the SSAUpdater. To avoid adding PHINodes, check if the value is
// available in UserBB, if not substitute undef.
Value *NewVal;
if (UserBB == OrigPreheader)
NewVal = OrigPreHeaderVal;
else if (SSA.HasValueForBlock(UserBB))
NewVal = SSA.GetValueInMiddleOfBlock(UserBB);
else
NewVal = UndefValue::get(OrigHeaderVal->getType());
U = MetadataAsValue::get(C, ValueAsMetadata::get(NewVal));
}
}
}
}
}
/// ProcessInstruction - Given an instruction in the loop, check to see if it
/// has any uses that are outside the current loop. If so, insert LCSSA PHI
/// nodes and rewrite the uses.
bool LCSSA::ProcessInstruction(Instruction *Inst,
const SmallVectorImpl<BasicBlock*> &ExitBlocks) {
SmallVector<Use*, 16> UsesToRewrite;
BasicBlock *InstBB = Inst->getParent();
for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end();
UI != E; ++UI) {
User *U = *UI;
BasicBlock *UserBB = cast<Instruction>(U)->getParent();
if (PHINode *PN = dyn_cast<PHINode>(U))
UserBB = PN->getIncomingBlock(UI);
if (InstBB != UserBB && !inLoop(UserBB))
UsesToRewrite.push_back(&UI.getUse());
}
// If there are no uses outside the loop, exit with no change.
if (UsesToRewrite.empty()) return false;
++NumLCSSA; // We are applying the transformation
// Invoke instructions are special in that their result value is not available
// along their unwind edge. The code below tests to see whether DomBB dominates
// the value, so adjust DomBB to the normal destination block, which is
// effectively where the value is first usable.
BasicBlock *DomBB = Inst->getParent();
if (InvokeInst *Inv = dyn_cast<InvokeInst>(Inst))
DomBB = Inv->getNormalDest();
DomTreeNode *DomNode = DT->getNode(DomBB);
SSAUpdater SSAUpdate;
SSAUpdate.Initialize(Inst->getType(), Inst->getName());
// Insert the LCSSA phi's into all of the exit blocks dominated by the
// value, and add them to the Phi's map.
for (SmallVectorImpl<BasicBlock*>::const_iterator BBI = ExitBlocks.begin(),
BBE = ExitBlocks.end(); BBI != BBE; ++BBI) {
BasicBlock *ExitBB = *BBI;
if (!DT->dominates(DomNode, DT->getNode(ExitBB))) continue;
// If we already inserted something for this BB, don't reprocess it.
if (SSAUpdate.HasValueForBlock(ExitBB)) continue;
PHINode *PN = PHINode::Create(Inst->getType(), Inst->getName()+".lcssa",
ExitBB->begin());
PN->reserveOperandSpace(PredCache.GetNumPreds(ExitBB));
// Add inputs from inside the loop for this PHI.
for (BasicBlock **PI = PredCache.GetPreds(ExitBB); *PI; ++PI) {
PN->addIncoming(Inst, *PI);
// If the exit block has a predecessor not within the loop, arrange for
// the incoming value use corresponding to that predecessor to be
// rewritten in terms of a different LCSSA PHI.
if (!inLoop(*PI))
UsesToRewrite.push_back(
&PN->getOperandUse(
PN->getOperandNumForIncomingValue(PN->getNumIncomingValues()-1)));
}
// Remember that this phi makes the value alive in this block.
SSAUpdate.AddAvailableValue(ExitBB, PN);
}
// Rewrite all uses outside the loop in terms of the new PHIs we just
// inserted.
for (unsigned i = 0, e = UsesToRewrite.size(); i != e; ++i) {
// If this use is in an exit block, rewrite to use the newly inserted PHI.
// This is required for correctness because SSAUpdate doesn't handle uses in
// the same block. It assumes the PHI we inserted is at the end of the
// block.
Instruction *User = cast<Instruction>(UsesToRewrite[i]->getUser());
BasicBlock *UserBB = User->getParent();
if (PHINode *PN = dyn_cast<PHINode>(User))
UserBB = PN->getIncomingBlock(*UsesToRewrite[i]);
if (isa<PHINode>(UserBB->begin()) &&
isExitBlock(UserBB, ExitBlocks)) {
UsesToRewrite[i]->set(UserBB->begin());
continue;
}
// Otherwise, do full PHI insertion.
SSAUpdate.RewriteUse(*UsesToRewrite[i]);
}
return true;
}
/// Given an instruction in the loop, check to see if it has any uses that are
/// outside the current loop. If so, insert LCSSA PHI nodes and rewrite the
/// uses.
static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
const SmallVectorImpl<BasicBlock *> &ExitBlocks,
PredIteratorCache &PredCache, LoopInfo *LI) {
SmallVector<Use *, 16> UsesToRewrite;
// Tokens cannot be used in PHI nodes, so we skip over them.
// We can run into tokens which are live out of a loop with catchswitch
// instructions in Windows EH if the catchswitch has one catchpad which
// is inside the loop and another which is not.
if (Inst.getType()->isTokenTy())
return false;
BasicBlock *InstBB = Inst.getParent();
for (Use &U : Inst.uses()) {
Instruction *User = cast<Instruction>(U.getUser());
BasicBlock *UserBB = User->getParent();
if (PHINode *PN = dyn_cast<PHINode>(User))
UserBB = PN->getIncomingBlock(U);
if (InstBB != UserBB && !L.contains(UserBB))
UsesToRewrite.push_back(&U);
}
// If there are no uses outside the loop, exit with no change.
if (UsesToRewrite.empty())
return false;
++NumLCSSA; // We are applying the transformation
// Invoke instructions are special in that their result value is not available
// along their unwind edge. The code below tests to see whether DomBB
// dominates the value, so adjust DomBB to the normal destination block,
// which is effectively where the value is first usable.
BasicBlock *DomBB = Inst.getParent();
if (InvokeInst *Inv = dyn_cast<InvokeInst>(&Inst))
DomBB = Inv->getNormalDest();
DomTreeNode *DomNode = DT.getNode(DomBB);
SmallVector<PHINode *, 16> AddedPHIs;
SmallVector<PHINode *, 8> PostProcessPHIs;
SSAUpdater SSAUpdate;
SSAUpdate.Initialize(Inst.getType(), Inst.getName());
// Insert the LCSSA phi's into all of the exit blocks dominated by the
// value, and add them to the Phi's map.
for (BasicBlock *ExitBB : ExitBlocks) {
if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
continue;
// If we already inserted something for this BB, don't reprocess it.
if (SSAUpdate.HasValueForBlock(ExitBB))
continue;
PHINode *PN = PHINode::Create(Inst.getType(), PredCache.size(ExitBB),
Inst.getName() + ".lcssa", &ExitBB->front());
// Add inputs from inside the loop for this PHI.
for (BasicBlock *Pred : PredCache.get(ExitBB)) {
PN->addIncoming(&Inst, Pred);
// If the exit block has a predecessor not within the loop, arrange for
// the incoming value use corresponding to that predecessor to be
// rewritten in terms of a different LCSSA PHI.
if (!L.contains(Pred))
UsesToRewrite.push_back(
&PN->getOperandUse(PN->getOperandNumForIncomingValue(
PN->getNumIncomingValues() - 1)));
}
AddedPHIs.push_back(PN);
// Remember that this phi makes the value alive in this block.
SSAUpdate.AddAvailableValue(ExitBB, PN);
// LoopSimplify might fail to simplify some loops (e.g. when indirect
// branches are involved). In such situations, it might happen that an exit
// for Loop L1 is the header of a disjoint Loop L2. Thus, when we create
// PHIs in such an exit block, we are also inserting PHIs into L2's header.
// This could break LCSSA form for L2 because these inserted PHIs can also
// have uses outside of L2. Remember all PHIs in such situation as to
// revisit than later on. FIXME: Remove this if indirectbr support into
// LoopSimplify gets improved.
if (auto *OtherLoop = LI->getLoopFor(ExitBB))
if (!L.contains(OtherLoop))
PostProcessPHIs.push_back(PN);
}
// Rewrite all uses outside the loop in terms of the new PHIs we just
// inserted.
for (Use *UseToRewrite : UsesToRewrite) {
// If this use is in an exit block, rewrite to use the newly inserted PHI.
// This is required for correctness because SSAUpdate doesn't handle uses in
// the same block. It assumes the PHI we inserted is at the end of the
// block.
Instruction *User = cast<Instruction>(UseToRewrite->getUser());
BasicBlock *UserBB = User->getParent();
if (PHINode *PN = dyn_cast<PHINode>(User))
UserBB = PN->getIncomingBlock(*UseToRewrite);
if (isa<PHINode>(UserBB->begin()) && isExitBlock(UserBB, ExitBlocks)) {
// Tell the VHs that the uses changed. This updates SCEV's caches.
if (UseToRewrite->get()->hasValueHandle())
ValueHandleBase::ValueIsRAUWd(*UseToRewrite, &UserBB->front());
UseToRewrite->set(&UserBB->front());
continue;
}
// Otherwise, do full PHI insertion.
SSAUpdate.RewriteUse(*UseToRewrite);
}
// Post process PHI instructions that were inserted into another disjoint loop
// and update their exits properly.
for (auto *I : PostProcessPHIs) {
if (I->use_empty())
continue;
BasicBlock *PHIBB = I->getParent();
Loop *OtherLoop = LI->getLoopFor(PHIBB);
SmallVector<BasicBlock *, 8> EBs;
OtherLoop->getExitBlocks(EBs);
if (EBs.empty())
continue;
// Recurse and re-process each PHI instruction. FIXME: we should really
// convert this entire thing to a worklist approach where we process a
// vector of instructions...
processInstruction(*OtherLoop, *I, DT, EBs, PredCache, LI);
}
// Remove PHI nodes that did not have any uses rewritten.
for (PHINode *PN : AddedPHIs)
if (PN->use_empty())
PN->eraseFromParent();
return true;
}
