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llvm-project/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp

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//===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This family of functions perform manipulations on basic blocks, and
// instructions contained within basic blocks.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
using namespace llvm;
void llvm::DeleteDeadBlock(BasicBlock *BB) {
assert((pred_begin(BB) == pred_end(BB) ||
// Can delete self loop.
BB->getSinglePredecessor() == BB) && "Block is not dead!");
TerminatorInst *BBTerm = BB->getTerminator();
// Loop through all of our successors and make sure they know that one
// of their predecessors is going away.
for (BasicBlock *Succ : BBTerm->successors())
Succ->removePredecessor(BB);
// Zap all the instructions in the block.
while (!BB->empty()) {
Instruction &I = BB->back();
// If this instruction is used, replace uses with an arbitrary value.
// Because control flow can't get here, we don't care what we replace the
// value with. Note that since this block is unreachable, and all values
// contained within it must dominate their uses, that all uses will
// eventually be removed (they are themselves dead).
if (!I.use_empty())
I.replaceAllUsesWith(UndefValue::get(I.getType()));
BB->getInstList().pop_back();
}
// Zap the block!
BB->eraseFromParent();
}
void llvm::FoldSingleEntryPHINodes(BasicBlock *BB,
MemoryDependenceResults *MemDep) {
if (!isa<PHINode>(BB->begin())) return;
while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
if (PN->getIncomingValue(0) != PN)
PN->replaceAllUsesWith(PN->getIncomingValue(0));
else
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
if (MemDep)
MemDep->removeInstruction(PN); // Memdep updates AA itself.
PN->eraseFromParent();
}
}
bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
// Recursively deleting a PHI may cause multiple PHIs to be deleted
// or RAUW'd undef, so use an array of WeakVH for the PHIs to delete.
SmallVector<WeakVH, 8> PHIs;
for (BasicBlock::iterator I = BB->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I)
PHIs.push_back(PN);
bool Changed = false;
for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
Changed |= RecursivelyDeleteDeadPHINode(PN, TLI);
return Changed;
}
bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT,
LoopInfo *LI,
MemoryDependenceResults *MemDep) {
// Don't merge away blocks who have their address taken.
if (BB->hasAddressTaken()) return false;
// Can't merge if there are multiple predecessors, or no predecessors.
BasicBlock *PredBB = BB->getUniquePredecessor();
if (!PredBB) return false;
// Don't break self-loops.
if (PredBB == BB) return false;
// Don't break unwinding instructions.
if (PredBB->getTerminator()->isExceptional())
return false;
succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
BasicBlock *OnlySucc = BB;
for (; SI != SE; ++SI)
if (*SI != OnlySucc) {
OnlySucc = nullptr; // There are multiple distinct successors!
break;
}
// Can't merge if there are multiple successors.
if (!OnlySucc) return false;
// Can't merge if there is PHI loop.
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
if (PHINode *PN = dyn_cast<PHINode>(BI)) {
for (Value *IncValue : PN->incoming_values())
if (IncValue == PN)
return false;
} else
break;
}
// Begin by getting rid of unneeded PHIs.
if (isa<PHINode>(BB->front()))
FoldSingleEntryPHINodes(BB, MemDep);
// Delete the unconditional branch from the predecessor...
PredBB->getInstList().pop_back();
// Make all PHI nodes that referred to BB now refer to Pred as their
// source...
BB->replaceAllUsesWith(PredBB);
// Move all definitions in the successor to the predecessor...
PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
// Inherit predecessors name if it exists.
if (!PredBB->hasName())
PredBB->takeName(BB);
// Finally, erase the old block and update dominator info.
if (DT)
if (DomTreeNode *DTN = DT->getNode(BB)) {
DomTreeNode *PredDTN = DT->getNode(PredBB);
SmallVector<DomTreeNode *, 8> Children(DTN->begin(), DTN->end());
for (SmallVectorImpl<DomTreeNode *>::iterator DI = Children.begin(),
DE = Children.end();
DI != DE; ++DI)
DT->changeImmediateDominator(*DI, PredDTN);
DT->eraseNode(BB);
}
if (LI)
LI->removeBlock(BB);
if (MemDep)
MemDep->invalidateCachedPredecessors();
BB->eraseFromParent();
return true;
}
void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
BasicBlock::iterator &BI, Value *V) {
Instruction &I = *BI;
// Replaces all of the uses of the instruction with uses of the value
I.replaceAllUsesWith(V);
// Make sure to propagate a name if there is one already.
if (I.hasName() && !V->hasName())
V->takeName(&I);
// Delete the unnecessary instruction now...
BI = BIL.erase(BI);
}
void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
BasicBlock::iterator &BI, Instruction *I) {
assert(I->getParent() == nullptr &&
"ReplaceInstWithInst: Instruction already inserted into basic block!");
// Copy debug location to newly added instruction, if it wasn't already set
// by the caller.
if (!I->getDebugLoc())
I->setDebugLoc(BI->getDebugLoc());
// Insert the new instruction into the basic block...
BasicBlock::iterator New = BIL.insert(BI, I);
// Replace all uses of the old instruction, and delete it.
ReplaceInstWithValue(BIL, BI, I);
// Move BI back to point to the newly inserted instruction
BI = New;
}
void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
BasicBlock::iterator BI(From);
ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
}
BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, DominatorTree *DT,
LoopInfo *LI) {
unsigned SuccNum = GetSuccessorNumber(BB, Succ);
// If this is a critical edge, let SplitCriticalEdge do it.
TerminatorInst *LatchTerm = BB->getTerminator();
if (SplitCriticalEdge(LatchTerm, SuccNum, CriticalEdgeSplittingOptions(DT, LI)
.setPreserveLCSSA()))
return LatchTerm->getSuccessor(SuccNum);
// If the edge isn't critical, then BB has a single successor or Succ has a
// single pred. Split the block.
if (BasicBlock *SP = Succ->getSinglePredecessor()) {
// If the successor only has a single pred, split the top of the successor
// block.
assert(SP == BB && "CFG broken");
SP = nullptr;
return SplitBlock(Succ, &Succ->front(), DT, LI);
}
// Otherwise, if BB has a single successor, split it at the bottom of the
// block.
assert(BB->getTerminator()->getNumSuccessors() == 1 &&
"Should have a single succ!");
return SplitBlock(BB, BB->getTerminator(), DT, LI);
}
unsigned
llvm::SplitAllCriticalEdges(Function &F,
const CriticalEdgeSplittingOptions &Options) {
unsigned NumBroken = 0;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
TerminatorInst *TI = I->getTerminator();
if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI))
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
if (SplitCriticalEdge(TI, i, Options))
++NumBroken;
}
return NumBroken;
}
BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
DominatorTree *DT, LoopInfo *LI) {
BasicBlock::iterator SplitIt = SplitPt->getIterator();
while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
++SplitIt;
BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
// The new block lives in whichever loop the old one did. This preserves
// LCSSA as well, because we force the split point to be after any PHI nodes.
if (LI)
if (Loop *L = LI->getLoopFor(Old))
L->addBasicBlockToLoop(New, *LI);
if (DT)
// Old dominates New. New node dominates all other nodes dominated by Old.
if (DomTreeNode *OldNode = DT->getNode(Old)) {
std::vector<DomTreeNode *> Children;
for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
I != E; ++I)
Children.push_back(*I);
DomTreeNode *NewNode = DT->addNewBlock(New, Old);
for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
E = Children.end(); I != E; ++I)
DT->changeImmediateDominator(*I, NewNode);
}
return New;
}
/// Update DominatorTree, LoopInfo, and LCCSA analysis information.
static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
ArrayRef<BasicBlock *> Preds,
DominatorTree *DT, LoopInfo *LI,
bool PreserveLCSSA, bool &HasLoopExit) {
// Update dominator tree if available.
if (DT)
DT->splitBlock(NewBB);
// The rest of the logic is only relevant for updating the loop structures.
if (!LI)
return;
Loop *L = LI->getLoopFor(OldBB);
// If we need to preserve loop analyses, collect some information about how
// this split will affect loops.
bool IsLoopEntry = !!L;
bool SplitMakesNewLoopHeader = false;
for (ArrayRef<BasicBlock *>::iterator i = Preds.begin(), e = Preds.end();
i != e; ++i) {
BasicBlock *Pred = *i;
// If we need to preserve LCSSA, determine if any of the preds is a loop
// exit.
if (PreserveLCSSA)
if (Loop *PL = LI->getLoopFor(Pred))
if (!PL->contains(OldBB))
HasLoopExit = true;
// If we need to preserve LoopInfo, note whether any of the preds crosses
// an interesting loop boundary.
if (!L)
continue;
if (L->contains(Pred))
IsLoopEntry = false;
else
SplitMakesNewLoopHeader = true;
}
// Unless we have a loop for OldBB, nothing else to do here.
if (!L)
return;
if (IsLoopEntry) {
// Add the new block to the nearest enclosing loop (and not an adjacent
// loop). To find this, examine each of the predecessors and determine which
// loops enclose them, and select the most-nested loop which contains the
// loop containing the block being split.
Loop *InnermostPredLoop = nullptr;
for (ArrayRef<BasicBlock*>::iterator
i = Preds.begin(), e = Preds.end(); i != e; ++i) {
BasicBlock *Pred = *i;
if (Loop *PredLoop = LI->getLoopFor(Pred)) {
// Seek a loop which actually contains the block being split (to avoid
// adjacent loops).
while (PredLoop && !PredLoop->contains(OldBB))
PredLoop = PredLoop->getParentLoop();
// Select the most-nested of these loops which contains the block.
if (PredLoop && PredLoop->contains(OldBB) &&
(!InnermostPredLoop ||
InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
InnermostPredLoop = PredLoop;
}
}
if (InnermostPredLoop)
InnermostPredLoop->addBasicBlockToLoop(NewBB, *LI);
} else {
L->addBasicBlockToLoop(NewBB, *LI);
if (SplitMakesNewLoopHeader)
L->moveToHeader(NewBB);
}
}
/// Update the PHI nodes in OrigBB to include the values coming from NewBB.
/// This also updates AliasAnalysis, if available.
static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
ArrayRef<BasicBlock *> Preds, BranchInst *BI,
bool HasLoopExit) {
// Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end());
for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
PHINode *PN = cast<PHINode>(I++);
// Check to see if all of the values coming in are the same. If so, we
// don't need to create a new PHI node, unless it's needed for LCSSA.
Value *InVal = nullptr;
if (!HasLoopExit) {
InVal = PN->getIncomingValueForBlock(Preds[0]);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
if (!PredSet.count(PN->getIncomingBlock(i)))
continue;
if (!InVal)
InVal = PN->getIncomingValue(i);
else if (InVal != PN->getIncomingValue(i)) {
InVal = nullptr;
break;
}
}
}
if (InVal) {
// If all incoming values for the new PHI would be the same, just don't
// make a new PHI. Instead, just remove the incoming values from the old
// PHI.
// NOTE! This loop walks backwards for a reason! First off, this minimizes
// the cost of removal if we end up removing a large number of values, and
// second off, this ensures that the indices for the incoming values
// aren't invalidated when we remove one.
for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i)
if (PredSet.count(PN->getIncomingBlock(i)))
PN->removeIncomingValue(i, false);
// Add an incoming value to the PHI node in the loop for the preheader
// edge.
PN->addIncoming(InVal, NewBB);
continue;
}
// If the values coming into the block are not the same, we need a new
// PHI.
// Create the new PHI node, insert it into NewBB at the end of the block
PHINode *NewPHI =
PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
// NOTE! This loop walks backwards for a reason! First off, this minimizes
// the cost of removal if we end up removing a large number of values, and
// second off, this ensures that the indices for the incoming values aren't
// invalidated when we remove one.
for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
BasicBlock *IncomingBB = PN->getIncomingBlock(i);
if (PredSet.count(IncomingBB)) {
Value *V = PN->removeIncomingValue(i, false);
NewPHI->addIncoming(V, IncomingBB);
}
}
PN->addIncoming(NewPHI, NewBB);
}
}
BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix, DominatorTree *DT,
LoopInfo *LI, bool PreserveLCSSA) {
// Do not attempt to split that which cannot be split.
if (!BB->canSplitPredecessors())
return nullptr;
// For the landingpads we need to act a bit differently.
// Delegate this work to the SplitLandingPadPredecessors.
if (BB->isLandingPad()) {
SmallVector<BasicBlock*, 2> NewBBs;
std::string NewName = std::string(Suffix) + ".split-lp";
SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(), NewBBs, DT,
LI, PreserveLCSSA);
return NewBBs[0];
}
// Create new basic block, insert right before the original block.
BasicBlock *NewBB = BasicBlock::Create(
BB->getContext(), BB->getName() + Suffix, BB->getParent(), BB);
// The new block unconditionally branches to the old block.
BranchInst *BI = BranchInst::Create(BB, NewBB);
BI->setDebugLoc(BB->getFirstNonPHI()->getDebugLoc());
// Move the edges from Preds to point to NewBB instead of BB.
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
// This is slightly more strict than necessary; the minimum requirement
// is that there be no more than one indirectbr branching to BB. And
// all BlockAddress uses would need to be updated.
assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
"Cannot split an edge from an IndirectBrInst");
Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
}
// Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
// node becomes an incoming value for BB's phi node. However, if the Preds
// list is empty, we need to insert dummy entries into the PHI nodes in BB to
// account for the newly created predecessor.
if (Preds.size() == 0) {
// Insert dummy values as the incoming value.
for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
return NewBB;
}
// Update DominatorTree, LoopInfo, and LCCSA analysis information.
bool HasLoopExit = false;
UpdateAnalysisInformation(BB, NewBB, Preds, DT, LI, PreserveLCSSA,
HasLoopExit);
// Update the PHI nodes in BB with the values coming from NewBB.
UpdatePHINodes(BB, NewBB, Preds, BI, HasLoopExit);
return NewBB;
}
void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix1, const char *Suffix2,
SmallVectorImpl<BasicBlock *> &NewBBs,
DominatorTree *DT, LoopInfo *LI,
bool PreserveLCSSA) {
assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
// Create a new basic block for OrigBB's predecessors listed in Preds. Insert
// it right before the original block.
BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
OrigBB->getName() + Suffix1,
OrigBB->getParent(), OrigBB);
NewBBs.push_back(NewBB1);
// The new block unconditionally branches to the old block.
BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
BI1->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
// Move the edges from Preds to point to NewBB1 instead of OrigBB.
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
// This is slightly more strict than necessary; the minimum requirement
// is that there be no more than one indirectbr branching to BB. And
// all BlockAddress uses would need to be updated.
assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
"Cannot split an edge from an IndirectBrInst");
Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
}
bool HasLoopExit = false;
UpdateAnalysisInformation(OrigBB, NewBB1, Preds, DT, LI, PreserveLCSSA,
HasLoopExit);
// Update the PHI nodes in OrigBB with the values coming from NewBB1.
UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, HasLoopExit);
// Move the remaining edges from OrigBB to point to NewBB2.
SmallVector<BasicBlock*, 8> NewBB2Preds;
for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
i != e; ) {
BasicBlock *Pred = *i++;
if (Pred == NewBB1) continue;
assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
"Cannot split an edge from an IndirectBrInst");
NewBB2Preds.push_back(Pred);
e = pred_end(OrigBB);
}
BasicBlock *NewBB2 = nullptr;
if (!NewBB2Preds.empty()) {
// Create another basic block for the rest of OrigBB's predecessors.
NewBB2 = BasicBlock::Create(OrigBB->getContext(),
OrigBB->getName() + Suffix2,
OrigBB->getParent(), OrigBB);
NewBBs.push_back(NewBB2);
// The new block unconditionally branches to the old block.
BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
BI2->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
// Move the remaining edges from OrigBB to point to NewBB2.
for (SmallVectorImpl<BasicBlock*>::iterator
i = NewBB2Preds.begin(), e = NewBB2Preds.end(); i != e; ++i)
(*i)->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
// Update DominatorTree, LoopInfo, and LCCSA analysis information.
HasLoopExit = false;
UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, DT, LI,
PreserveLCSSA, HasLoopExit);
// Update the PHI nodes in OrigBB with the values coming from NewBB2.
UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, HasLoopExit);
}
LandingPadInst *LPad = OrigBB->getLandingPadInst();
Instruction *Clone1 = LPad->clone();
Clone1->setName(Twine("lpad") + Suffix1);
NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
if (NewBB2) {
Instruction *Clone2 = LPad->clone();
Clone2->setName(Twine("lpad") + Suffix2);
NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
// Create a PHI node for the two cloned landingpad instructions only
// if the original landingpad instruction has some uses.
if (!LPad->use_empty()) {
assert(!LPad->getType()->isTokenTy() &&
"Split cannot be applied if LPad is token type. Otherwise an "
"invalid PHINode of token type would be created.");
PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
PN->addIncoming(Clone1, NewBB1);
PN->addIncoming(Clone2, NewBB2);
LPad->replaceAllUsesWith(PN);
}
LPad->eraseFromParent();
} else {
// There is no second clone. Just replace the landing pad with the first
// clone.
LPad->replaceAllUsesWith(Clone1);
LPad->eraseFromParent();
}
}
ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
BasicBlock *Pred) {
Instruction *UncondBranch = Pred->getTerminator();
// Clone the return and add it to the end of the predecessor.
Instruction *NewRet = RI->clone();
Pred->getInstList().push_back(NewRet);
// If the return instruction returns a value, and if the value was a
// PHI node in "BB", propagate the right value into the return.
for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
i != e; ++i) {
Value *V = *i;
Instruction *NewBC = nullptr;
if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
// Return value might be bitcasted. Clone and insert it before the
// return instruction.
V = BCI->getOperand(0);
NewBC = BCI->clone();
Pred->getInstList().insert(NewRet->getIterator(), NewBC);
*i = NewBC;
}
if (PHINode *PN = dyn_cast<PHINode>(V)) {
if (PN->getParent() == BB) {
if (NewBC)
NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
else
*i = PN->getIncomingValueForBlock(Pred);
}
}
}
// Update any PHI nodes in the returning block to realize that we no
// longer branch to them.
BB->removePredecessor(Pred);
UncondBranch->eraseFromParent();
return cast<ReturnInst>(NewRet);
}
TerminatorInst *
llvm::SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
bool Unreachable, MDNode *BranchWeights,
DominatorTree *DT, LoopInfo *LI) {
BasicBlock *Head = SplitBefore->getParent();
BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
TerminatorInst *HeadOldTerm = Head->getTerminator();
LLVMContext &C = Head->getContext();
BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
TerminatorInst *CheckTerm;
if (Unreachable)
CheckTerm = new UnreachableInst(C, ThenBlock);
else
CheckTerm = BranchInst::Create(Tail, ThenBlock);
CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
BranchInst *HeadNewTerm =
BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
if (DT) {
if (DomTreeNode *OldNode = DT->getNode(Head)) {
std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
for (auto Child : Children)
DT->changeImmediateDominator(Child, NewNode);
// Head dominates ThenBlock.
DT->addNewBlock(ThenBlock, Head);
}
}
if (LI) {
Loop *L = LI->getLoopFor(Head);
L->addBasicBlockToLoop(ThenBlock, *LI);
L->addBasicBlockToLoop(Tail, *LI);
}
return CheckTerm;
}
void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
TerminatorInst **ThenTerm,
TerminatorInst **ElseTerm,
MDNode *BranchWeights) {
BasicBlock *Head = SplitBefore->getParent();
BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
TerminatorInst *HeadOldTerm = Head->getTerminator();
LLVMContext &C = Head->getContext();
BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
*ThenTerm = BranchInst::Create(Tail, ThenBlock);
(*ThenTerm)->setDebugLoc(SplitBefore->getDebugLoc());
*ElseTerm = BranchInst::Create(Tail, ElseBlock);
(*ElseTerm)->setDebugLoc(SplitBefore->getDebugLoc());
BranchInst *HeadNewTerm =
BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond);
HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
}
Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
BasicBlock *&IfFalse) {
PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
BasicBlock *Pred1 = nullptr;
BasicBlock *Pred2 = nullptr;
if (SomePHI) {
if (SomePHI->getNumIncomingValues() != 2)
return nullptr;
Pred1 = SomePHI->getIncomingBlock(0);
Pred2 = SomePHI->getIncomingBlock(1);
} else {
pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
if (PI == PE) // No predecessor
return nullptr;
Pred1 = *PI++;
if (PI == PE) // Only one predecessor
return nullptr;
Pred2 = *PI++;
if (PI != PE) // More than two predecessors
return nullptr;
}
// We can only handle branches. Other control flow will be lowered to
// branches if possible anyway.
BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
if (!Pred1Br || !Pred2Br)
return nullptr;
// Eliminate code duplication by ensuring that Pred1Br is conditional if
// either are.
if (Pred2Br->isConditional()) {
// If both branches are conditional, we don't have an "if statement". In
// reality, we could transform this case, but since the condition will be
// required anyway, we stand no chance of eliminating it, so the xform is
// probably not profitable.
if (Pred1Br->isConditional())
return nullptr;
std::swap(Pred1, Pred2);
std::swap(Pred1Br, Pred2Br);
}
if (Pred1Br->isConditional()) {
// The only thing we have to watch out for here is to make sure that Pred2
// doesn't have incoming edges from other blocks. If it does, the condition
// doesn't dominate BB.
if (!Pred2->getSinglePredecessor())
return nullptr;
// If we found a conditional branch predecessor, make sure that it branches
// to BB and Pred2Br. If it doesn't, this isn't an "if statement".
if (Pred1Br->getSuccessor(0) == BB &&
Pred1Br->getSuccessor(1) == Pred2) {
IfTrue = Pred1;
IfFalse = Pred2;
} else if (Pred1Br->getSuccessor(0) == Pred2 &&
Pred1Br->getSuccessor(1) == BB) {
IfTrue = Pred2;
IfFalse = Pred1;
} else {
// We know that one arm of the conditional goes to BB, so the other must
// go somewhere unrelated, and this must not be an "if statement".
return nullptr;
}
return Pred1Br->getCondition();
}
// Ok, if we got here, both predecessors end with an unconditional branch to
// BB. Don't panic! If both blocks only have a single (identical)
// predecessor, and THAT is a conditional branch, then we're all ok!
BasicBlock *CommonPred = Pred1->getSinglePredecessor();
if (CommonPred == nullptr || CommonPred != Pred2->getSinglePredecessor())
return nullptr;
// Otherwise, if this is a conditional branch, then we can use it!
BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
if (!BI) return nullptr;
assert(BI->isConditional() && "Two successors but not conditional?");
if (BI->getSuccessor(0) == Pred1) {
IfTrue = Pred1;
IfFalse = Pred2;
} else {
IfTrue = Pred2;
IfFalse = Pred1;
}
return BI->getCondition();
}
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