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

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//===- BasicBlockUtils.cpp - BasicBlock Utilities --------------------------==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This family of functions perform manipulations on basic blocks, and
// instructions contained within basic blocks.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Analysis/MemorySSAUpdater.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/PseudoProbe.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
#include <cassert>
#include <cstdint>
#include <string>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "basicblock-utils"
void llvm::DetatchDeadBlocks(
ArrayRef<BasicBlock *> BBs,
SmallVectorImpl<DominatorTree::UpdateType> *Updates,
bool KeepOneInputPHIs) {
for (auto *BB : BBs) {
// Loop through all of our successors and make sure they know that one
// of their predecessors is going away.
SmallPtrSet<BasicBlock *, 4> UniqueSuccessors;
for (BasicBlock *Succ : successors(BB)) {
Succ->removePredecessor(BB, KeepOneInputPHIs);
if (Updates && UniqueSuccessors.insert(Succ).second)
Updates->push_back({DominatorTree::Delete, BB, Succ});
}
// 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();
}
new UnreachableInst(BB->getContext(), BB);
assert(BB->getInstList().size() == 1 &&
isa<UnreachableInst>(BB->getTerminator()) &&
"The successor list of BB isn't empty before "
"applying corresponding DTU updates.");
}
}
void llvm::DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU,
bool KeepOneInputPHIs) {
DeleteDeadBlocks({BB}, DTU, KeepOneInputPHIs);
}
void llvm::DeleteDeadBlocks(ArrayRef <BasicBlock *> BBs, DomTreeUpdater *DTU,
bool KeepOneInputPHIs) {
#ifndef NDEBUG
// Make sure that all predecessors of each dead block is also dead.
SmallPtrSet<BasicBlock *, 4> Dead(BBs.begin(), BBs.end());
assert(Dead.size() == BBs.size() && "Duplicating blocks?");
for (auto *BB : Dead)
for (BasicBlock *Pred : predecessors(BB))
assert(Dead.count(Pred) && "All predecessors must be dead!");
#endif
SmallVector<DominatorTree::UpdateType, 4> Updates;
DetatchDeadBlocks(BBs, DTU ? &Updates : nullptr, KeepOneInputPHIs);
if (DTU)
DTU->applyUpdates(Updates);
for (BasicBlock *BB : BBs)
if (DTU)
DTU->deleteBB(BB);
else
BB->eraseFromParent();
}
bool llvm::EliminateUnreachableBlocks(Function &F, DomTreeUpdater *DTU,
bool KeepOneInputPHIs) {
df_iterator_default_set<BasicBlock*> Reachable;
// Mark all reachable blocks.
for (BasicBlock *BB : depth_first_ext(&F, Reachable))
(void)BB/* Mark all reachable blocks */;
// Collect all dead blocks.
std::vector<BasicBlock*> DeadBlocks;
for (BasicBlock &BB : F)
if (!Reachable.count(&BB))
DeadBlocks.push_back(&BB);
// Delete the dead blocks.
DeleteDeadBlocks(DeadBlocks, DTU, KeepOneInputPHIs);
return !DeadBlocks.empty();
}
bool llvm::FoldSingleEntryPHINodes(BasicBlock *BB,
MemoryDependenceResults *MemDep) {
if (!isa<PHINode>(BB->begin()))
return false;
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();
}
return true;
}
bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI,
MemorySSAUpdater *MSSAU) {
// Recursively deleting a PHI may cause multiple PHIs to be deleted
// or RAUW'd undef, so use an array of WeakTrackingVH for the PHIs to delete.
SmallVector<WeakTrackingVH, 8> PHIs;
for (PHINode &PN : BB->phis())
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, MSSAU);
return Changed;
}
bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
LoopInfo *LI, MemorySSAUpdater *MSSAU,
MemoryDependenceResults *MemDep,
bool PredecessorWithTwoSuccessors) {
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()->isExceptionalTerminator())
return false;
// Can't merge if there are multiple distinct successors.
if (!PredecessorWithTwoSuccessors && PredBB->getUniqueSuccessor() != BB)
return false;
// Currently only allow PredBB to have two predecessors, one being BB.
// Update BI to branch to BB's only successor instead of BB.
BranchInst *PredBB_BI;
BasicBlock *NewSucc = nullptr;
unsigned FallThruPath;
if (PredecessorWithTwoSuccessors) {
if (!(PredBB_BI = dyn_cast<BranchInst>(PredBB->getTerminator())))
return false;
BranchInst *BB_JmpI = dyn_cast<BranchInst>(BB->getTerminator());
if (!BB_JmpI || !BB_JmpI->isUnconditional())
return false;
NewSucc = BB_JmpI->getSuccessor(0);
FallThruPath = PredBB_BI->getSuccessor(0) == BB ? 0 : 1;
}
// Can't merge if there is PHI loop.
for (PHINode &PN : BB->phis())
if (llvm::is_contained(PN.incoming_values(), &PN))
return false;
LLVM_DEBUG(dbgs() << "Merging: " << BB->getName() << " into "
<< PredBB->getName() << "\n");
// Begin by getting rid of unneeded PHIs.
SmallVector<AssertingVH<Value>, 4> IncomingValues;
if (isa<PHINode>(BB->front())) {
for (PHINode &PN : BB->phis())
if (!isa<PHINode>(PN.getIncomingValue(0)) ||
cast<PHINode>(PN.getIncomingValue(0))->getParent() != BB)
IncomingValues.push_back(PN.getIncomingValue(0));
FoldSingleEntryPHINodes(BB, MemDep);
}
// DTU update: Collect all the edges that exit BB.
// These dominator edges will be redirected from Pred.
std::vector<DominatorTree::UpdateType> Updates;
if (DTU) {
SmallSetVector<BasicBlock *, 2> UniqueSuccessors(succ_begin(BB),
succ_end(BB));
Updates.reserve(1 + (2 * UniqueSuccessors.size()));
// Add insert edges first. Experimentally, for the particular case of two
// blocks that can be merged, with a single successor and single predecessor
// respectively, it is beneficial to have all insert updates first. Deleting
// edges first may lead to unreachable blocks, followed by inserting edges
// making the blocks reachable again. Such DT updates lead to high compile
// times. We add inserts before deletes here to reduce compile time.
for (BasicBlock *UniqueSuccessor : UniqueSuccessors)
// This successor of BB may already have PredBB as a predecessor.
if (!llvm::is_contained(successors(PredBB), UniqueSuccessor))
Updates.push_back({DominatorTree::Insert, PredBB, UniqueSuccessor});
for (BasicBlock *UniqueSuccessor : UniqueSuccessors)
Updates.push_back({DominatorTree::Delete, BB, UniqueSuccessor});
Updates.push_back({DominatorTree::Delete, PredBB, BB});
}
Instruction *PTI = PredBB->getTerminator();
Instruction *STI = BB->getTerminator();
Instruction *Start = &*BB->begin();
// If there's nothing to move, mark the starting instruction as the last
// instruction in the block. Terminator instruction is handled separately.
if (Start == STI)
Start = PTI;
// Move all definitions in the successor to the predecessor...
PredBB->getInstList().splice(PTI->getIterator(), BB->getInstList(),
BB->begin(), STI->getIterator());
if (MSSAU)
MSSAU->moveAllAfterMergeBlocks(BB, PredBB, Start);
// Make all PHI nodes that referred to BB now refer to Pred as their
// source...
BB->replaceAllUsesWith(PredBB);
if (PredecessorWithTwoSuccessors) {
// Delete the unconditional branch from BB.
BB->getInstList().pop_back();
// Update branch in the predecessor.
PredBB_BI->setSuccessor(FallThruPath, NewSucc);
} else {
// Delete the unconditional branch from the predecessor.
PredBB->getInstList().pop_back();
// Move terminator instruction.
PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
// Terminator may be a memory accessing instruction too.
if (MSSAU)
if (MemoryUseOrDef *MUD = cast_or_null<MemoryUseOrDef>(
MSSAU->getMemorySSA()->getMemoryAccess(PredBB->getTerminator())))
MSSAU->moveToPlace(MUD, PredBB, MemorySSA::End);
}
// Add unreachable to now empty BB.
new UnreachableInst(BB->getContext(), BB);
// Inherit predecessors name if it exists.
if (!PredBB->hasName())
PredBB->takeName(BB);
if (LI)
LI->removeBlock(BB);
if (MemDep)
MemDep->invalidateCachedPredecessors();
// Finally, erase the old block and update dominator info.
if (DTU) {
assert(BB->getInstList().size() == 1 &&
isa<UnreachableInst>(BB->getTerminator()) &&
"The successor list of BB isn't empty before "
"applying corresponding DTU updates.");
DTU->applyUpdates(Updates);
DTU->deleteBB(BB);
} else {
BB->eraseFromParent(); // Nuke BB if DTU is nullptr.
}
return true;
}
bool llvm::MergeBlockSuccessorsIntoGivenBlocks(
SmallPtrSetImpl<BasicBlock *> &MergeBlocks, Loop *L, DomTreeUpdater *DTU,
LoopInfo *LI) {
assert(!MergeBlocks.empty() && "MergeBlocks should not be empty");
bool BlocksHaveBeenMerged = false;
while (!MergeBlocks.empty()) {
BasicBlock *BB = *MergeBlocks.begin();
BasicBlock *Dest = BB->getSingleSuccessor();
if (Dest && (!L || L->contains(Dest))) {
BasicBlock *Fold = Dest->getUniquePredecessor();
(void)Fold;
if (MergeBlockIntoPredecessor(Dest, DTU, LI)) {
assert(Fold == BB &&
"Expecting BB to be unique predecessor of the Dest block");
MergeBlocks.erase(Dest);
BlocksHaveBeenMerged = true;
} else
MergeBlocks.erase(BB);
} else
MergeBlocks.erase(BB);
}
return BlocksHaveBeenMerged;
}
/// Remove redundant instructions within sequences of consecutive dbg.value
/// instructions. This is done using a backward scan to keep the last dbg.value
/// describing a specific variable/fragment.
///
/// BackwardScan strategy:
/// ----------------------
/// Given a sequence of consecutive DbgValueInst like this
///
/// dbg.value ..., "x", FragmentX1 (*)
/// dbg.value ..., "y", FragmentY1
/// dbg.value ..., "x", FragmentX2
/// dbg.value ..., "x", FragmentX1 (**)
///
/// then the instruction marked with (*) can be removed (it is guaranteed to be
/// obsoleted by the instruction marked with (**) as the latter instruction is
/// describing the same variable using the same fragment info).
///
/// Possible improvements:
/// - Check fully overlapping fragments and not only identical fragments.
/// - Support dbg.addr, dbg.declare. dbg.label, and possibly other meta
/// instructions being part of the sequence of consecutive instructions.
static bool removeRedundantDbgInstrsUsingBackwardScan(BasicBlock *BB) {
SmallVector<DbgValueInst *, 8> ToBeRemoved;
SmallDenseSet<DebugVariable> VariableSet;
for (auto &I : reverse(*BB)) {
if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(&I)) {
DebugVariable Key(DVI->getVariable(),
DVI->getExpression(),
DVI->getDebugLoc()->getInlinedAt());
auto R = VariableSet.insert(Key);
// If the same variable fragment is described more than once it is enough
// to keep the last one (i.e. the first found since we for reverse
// iteration).
if (!R.second)
ToBeRemoved.push_back(DVI);
continue;
}
// Sequence with consecutive dbg.value instrs ended. Clear the map to
// restart identifying redundant instructions if case we find another
// dbg.value sequence.
VariableSet.clear();
}
for (auto &Instr : ToBeRemoved)
Instr->eraseFromParent();
return !ToBeRemoved.empty();
}
/// Remove redundant dbg.value instructions using a forward scan. This can
/// remove a dbg.value instruction that is redundant due to indicating that a
/// variable has the same value as already being indicated by an earlier
/// dbg.value.
///
/// ForwardScan strategy:
/// ---------------------
/// Given two identical dbg.value instructions, separated by a block of
/// instructions that isn't describing the same variable, like this
///
/// dbg.value X1, "x", FragmentX1 (**)
/// <block of instructions, none being "dbg.value ..., "x", ...">
/// dbg.value X1, "x", FragmentX1 (*)
///
/// then the instruction marked with (*) can be removed. Variable "x" is already
/// described as being mapped to the SSA value X1.
///
/// Possible improvements:
/// - Keep track of non-overlapping fragments.
static bool removeRedundantDbgInstrsUsingForwardScan(BasicBlock *BB) {
SmallVector<DbgValueInst *, 8> ToBeRemoved;
DenseMap<DebugVariable, std::pair<SmallVector<Value *, 4>, DIExpression *>>
VariableMap;
for (auto &I : *BB) {
if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(&I)) {
DebugVariable Key(DVI->getVariable(),
NoneType(),
DVI->getDebugLoc()->getInlinedAt());
auto VMI = VariableMap.find(Key);
// Update the map if we found a new value/expression describing the
// variable, or if the variable wasn't mapped already.
SmallVector<Value *, 4> Values(DVI->getValues());
if (VMI == VariableMap.end() || VMI->second.first != Values ||
VMI->second.second != DVI->getExpression()) {
VariableMap[Key] = {Values, DVI->getExpression()};
continue;
}
// Found an identical mapping. Remember the instruction for later removal.
ToBeRemoved.push_back(DVI);
}
}
for (auto &Instr : ToBeRemoved)
Instr->eraseFromParent();
return !ToBeRemoved.empty();
}
bool llvm::RemoveRedundantDbgInstrs(BasicBlock *BB, bool RemovePseudoOp) {
bool MadeChanges = false;
// By using the "backward scan" strategy before the "forward scan" strategy we
// can remove both dbg.value (2) and (3) in a situation like this:
//
// (1) dbg.value V1, "x", DIExpression()
// ...
// (2) dbg.value V2, "x", DIExpression()
// (3) dbg.value V1, "x", DIExpression()
//
// The backward scan will remove (2), it is made obsolete by (3). After
// getting (2) out of the way, the foward scan will remove (3) since "x"
// already is described as having the value V1 at (1).
MadeChanges |= removeRedundantDbgInstrsUsingBackwardScan(BB);
MadeChanges |= removeRedundantDbgInstrsUsingForwardScan(BB);
if (RemovePseudoOp)
MadeChanges |= removeRedundantPseudoProbes(BB);
if (MadeChanges)
LLVM_DEBUG(dbgs() << "Removed redundant dbg instrs from: "
<< BB->getName() << "\n");
return MadeChanges;
}
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, MemorySSAUpdater *MSSAU,
const Twine &BBName) {
unsigned SuccNum = GetSuccessorNumber(BB, Succ);
// If this is a critical edge, let SplitCriticalEdge do it.
Instruction *LatchTerm = BB->getTerminator();
if (SplitCriticalEdge(
LatchTerm, SuccNum,
CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA(),
BBName))
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, MSSAU, BBName,
/*Before=*/true);
}
// 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, MSSAU, BBName);
}
unsigned
llvm::SplitAllCriticalEdges(Function &F,
const CriticalEdgeSplittingOptions &Options) {
unsigned NumBroken = 0;
for (BasicBlock &BB : F) {
Instruction *TI = BB.getTerminator();
if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI) &&
!isa<CallBrInst>(TI))
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
if (SplitCriticalEdge(TI, i, Options))
++NumBroken;
}
return NumBroken;
}
static BasicBlock *SplitBlockImpl(BasicBlock *Old, Instruction *SplitPt,
DomTreeUpdater *DTU, DominatorTree *DT,
LoopInfo *LI, MemorySSAUpdater *MSSAU,
const Twine &BBName, bool Before) {
if (Before) {
DomTreeUpdater LocalDTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
return splitBlockBefore(Old, SplitPt,
DTU ? DTU : (DT ? &LocalDTU : nullptr), LI, MSSAU,
BBName);
}
BasicBlock::iterator SplitIt = SplitPt->getIterator();
while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
++SplitIt;
std::string Name = BBName.str();
BasicBlock *New = Old->splitBasicBlock(
SplitIt, Name.empty() ? Old->getName() + ".split" : Name);
// 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 (DTU) {
SmallVector<DominatorTree::UpdateType, 8> Updates;
// Old dominates New. New node dominates all other nodes dominated by Old.
SmallSetVector<BasicBlock *, 8> UniqueSuccessorsOfOld(succ_begin(New),
succ_end(New));
Updates.push_back({DominatorTree::Insert, Old, New});
Updates.reserve(Updates.size() + 2 * UniqueSuccessorsOfOld.size());
for (BasicBlock *UniqueSuccessorOfOld : UniqueSuccessorsOfOld) {
Updates.push_back({DominatorTree::Insert, New, UniqueSuccessorOfOld});
Updates.push_back({DominatorTree::Delete, Old, UniqueSuccessorOfOld});
}
DTU->applyUpdates(Updates);
} else if (DT)
// Old dominates New. New node dominates all other nodes dominated by Old.
if (DomTreeNode *OldNode = DT->getNode(Old)) {
std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
DomTreeNode *NewNode = DT->addNewBlock(New, Old);
for (DomTreeNode *I : Children)
DT->changeImmediateDominator(I, NewNode);
}
// Move MemoryAccesses still tracked in Old, but part of New now.
// Update accesses in successor blocks accordingly.
if (MSSAU)
MSSAU->moveAllAfterSpliceBlocks(Old, New, &*(New->begin()));
return New;
}
BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
DominatorTree *DT, LoopInfo *LI,
MemorySSAUpdater *MSSAU, const Twine &BBName,
bool Before) {
return SplitBlockImpl(Old, SplitPt, /*DTU=*/nullptr, DT, LI, MSSAU, BBName,
Before);
}
BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
DomTreeUpdater *DTU, LoopInfo *LI,
MemorySSAUpdater *MSSAU, const Twine &BBName,
bool Before) {
return SplitBlockImpl(Old, SplitPt, DTU, /*DT=*/nullptr, LI, MSSAU, BBName,
Before);
}
BasicBlock *llvm::splitBlockBefore(BasicBlock *Old, Instruction *SplitPt,
DomTreeUpdater *DTU, LoopInfo *LI,
MemorySSAUpdater *MSSAU,
const Twine &BBName) {
BasicBlock::iterator SplitIt = SplitPt->getIterator();
while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
++SplitIt;
std::string Name = BBName.str();
BasicBlock *New = Old->splitBasicBlock(
SplitIt, Name.empty() ? Old->getName() + ".split" : Name,
/* Before=*/true);
// 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 (DTU) {
SmallVector<DominatorTree::UpdateType, 8> DTUpdates;
// New dominates Old. The predecessor nodes of the Old node dominate
// New node.
SmallSetVector<BasicBlock *, 8> UniquePredecessorsOfOld(pred_begin(New),
pred_end(New));
DTUpdates.push_back({DominatorTree::Insert, New, Old});
DTUpdates.reserve(DTUpdates.size() + 2 * UniquePredecessorsOfOld.size());
for (BasicBlock *UniquePredecessorOfOld : UniquePredecessorsOfOld) {
DTUpdates.push_back({DominatorTree::Insert, UniquePredecessorOfOld, New});
DTUpdates.push_back({DominatorTree::Delete, UniquePredecessorOfOld, Old});
}
DTU->applyUpdates(DTUpdates);
// Move MemoryAccesses still tracked in Old, but part of New now.
// Update accesses in successor blocks accordingly.
if (MSSAU) {
MSSAU->applyUpdates(DTUpdates, DTU->getDomTree());
if (VerifyMemorySSA)
MSSAU->getMemorySSA()->verifyMemorySSA();
}
}
return New;
}
/// Update DominatorTree, LoopInfo, and LCCSA analysis information.
static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
ArrayRef<BasicBlock *> Preds,
DomTreeUpdater *DTU, DominatorTree *DT,
LoopInfo *LI, MemorySSAUpdater *MSSAU,
bool PreserveLCSSA, bool &HasLoopExit) {
// Update dominator tree if available.
if (DTU) {
// Recalculation of DomTree is needed when updating a forward DomTree and
// the Entry BB is replaced.
if (NewBB == &NewBB->getParent()->getEntryBlock() && DTU->hasDomTree()) {
// The entry block was removed and there is no external interface for
// the dominator tree to be notified of this change. In this corner-case
// we recalculate the entire tree.
DTU->recalculate(*NewBB->getParent());
} else {
// Split block expects NewBB to have a non-empty set of predecessors.
SmallVector<DominatorTree::UpdateType, 8> Updates;
SmallSetVector<BasicBlock *, 8> UniquePreds(Preds.begin(), Preds.end());
Updates.push_back({DominatorTree::Insert, NewBB, OldBB});
Updates.reserve(Updates.size() + 2 * UniquePreds.size());
for (auto *UniquePred : UniquePreds) {
Updates.push_back({DominatorTree::Insert, UniquePred, NewBB});
Updates.push_back({DominatorTree::Delete, UniquePred, OldBB});
}
DTU->applyUpdates(Updates);
}
} else if (DT) {
if (OldBB == DT->getRootNode()->getBlock()) {
assert(NewBB == &NewBB->getParent()->getEntryBlock());
DT->setNewRoot(NewBB);
} else {
// Split block expects NewBB to have a non-empty set of predecessors.
DT->splitBlock(NewBB);
}
}
// Update MemoryPhis after split if MemorySSA is available
if (MSSAU)
MSSAU->wireOldPredecessorsToNewImmediatePredecessor(OldBB, NewBB, Preds);
// The rest of the logic is only relevant for updating the loop structures.
if (!LI)
return;
if (DTU && DTU->hasDomTree())
DT = &DTU->getDomTree();
assert(DT && "DT should be available to update LoopInfo!");
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 (BasicBlock *Pred : Preds) {
// Preds that are not reachable from entry should not be used to identify if
// OldBB is a loop entry or if SplitMakesNewLoopHeader. Unreachable blocks
// are not within any loops, so we incorrectly mark SplitMakesNewLoopHeader
// as true and make the NewBB the header of some loop. This breaks LI.
if (!DT->isReachableFromEntry(Pred))
continue;
// 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 (BasicBlock *Pred : Preds) {
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);
}
}
static void SplitLandingPadPredecessorsImpl(
BasicBlock *OrigBB, ArrayRef<BasicBlock *> Preds, const char *Suffix1,
const char *Suffix2, SmallVectorImpl<BasicBlock *> &NewBBs,
DomTreeUpdater *DTU, DominatorTree *DT, LoopInfo *LI,
MemorySSAUpdater *MSSAU, bool PreserveLCSSA);
static BasicBlock *
SplitBlockPredecessorsImpl(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
const char *Suffix, DomTreeUpdater *DTU,
DominatorTree *DT, LoopInfo *LI,
MemorySSAUpdater *MSSAU, 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";
SplitLandingPadPredecessorsImpl(BB, Preds, Suffix, NewName.c_str(), NewBBs,
DTU, DT, LI, MSSAU, 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);
Loop *L = nullptr;
BasicBlock *OldLatch = nullptr;
// Splitting the predecessors of a loop header creates a preheader block.
if (LI && LI->isLoopHeader(BB)) {
L = LI->getLoopFor(BB);
// Using the loop start line number prevents debuggers stepping into the
// loop body for this instruction.
BI->setDebugLoc(L->getStartLoc());
// If BB is the header of the Loop, it is possible that the loop is
// modified, such that the current latch does not remain the latch of the
// loop. If that is the case, the loop metadata from the current latch needs
// to be applied to the new latch.
OldLatch = L->getLoopLatch();
} else
BI->setDebugLoc(BB->getFirstNonPHIOrDbg()->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");
assert(!isa<CallBrInst>(Preds[i]->getTerminator()) &&
"Cannot split an edge from a CallBrInst");
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.empty()) {
// 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);
}
// Update DominatorTree, LoopInfo, and LCCSA analysis information.
bool HasLoopExit = false;
UpdateAnalysisInformation(BB, NewBB, Preds, DTU, DT, LI, MSSAU, PreserveLCSSA,
HasLoopExit);
if (!Preds.empty()) {
// Update the PHI nodes in BB with the values coming from NewBB.
UpdatePHINodes(BB, NewBB, Preds, BI, HasLoopExit);
}
if (OldLatch) {
BasicBlock *NewLatch = L->getLoopLatch();
if (NewLatch != OldLatch) {
MDNode *MD = OldLatch->getTerminator()->getMetadata("llvm.loop");
NewLatch->getTerminator()->setMetadata("llvm.loop", MD);
OldLatch->getTerminator()->setMetadata("llvm.loop", nullptr);
}
}
return NewBB;
}
BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix, DominatorTree *DT,
LoopInfo *LI, MemorySSAUpdater *MSSAU,
bool PreserveLCSSA) {
return SplitBlockPredecessorsImpl(BB, Preds, Suffix, /*DTU=*/nullptr, DT, LI,
MSSAU, PreserveLCSSA);
}
BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix,
DomTreeUpdater *DTU, LoopInfo *LI,
MemorySSAUpdater *MSSAU,
bool PreserveLCSSA) {
return SplitBlockPredecessorsImpl(BB, Preds, Suffix, DTU,
/*DT=*/nullptr, LI, MSSAU, PreserveLCSSA);
}
static void SplitLandingPadPredecessorsImpl(
BasicBlock *OrigBB, ArrayRef<BasicBlock *> Preds, const char *Suffix1,
const char *Suffix2, SmallVectorImpl<BasicBlock *> &NewBBs,
DomTreeUpdater *DTU, DominatorTree *DT, LoopInfo *LI,
MemorySSAUpdater *MSSAU, 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, DTU, DT, LI, MSSAU,
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 (BasicBlock *NewBB2Pred : NewBB2Preds)
NewBB2Pred->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
// Update DominatorTree, LoopInfo, and LCCSA analysis information.
HasLoopExit = false;
UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, DTU, DT, LI, MSSAU,
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();
}
}
void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix1, const char *Suffix2,
SmallVectorImpl<BasicBlock *> &NewBBs,
DominatorTree *DT, LoopInfo *LI,
MemorySSAUpdater *MSSAU,
bool PreserveLCSSA) {
return SplitLandingPadPredecessorsImpl(
OrigBB, Preds, Suffix1, Suffix2, NewBBs,
/*DTU=*/nullptr, DT, LI, MSSAU, PreserveLCSSA);
}
void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix1, const char *Suffix2,
SmallVectorImpl<BasicBlock *> &NewBBs,
DomTreeUpdater *DTU, LoopInfo *LI,
MemorySSAUpdater *MSSAU,
bool PreserveLCSSA) {
return SplitLandingPadPredecessorsImpl(OrigBB, Preds, Suffix1, Suffix2,
NewBBs, DTU, /*DT=*/nullptr, LI, MSSAU,
PreserveLCSSA);
}
ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
BasicBlock *Pred,
DomTreeUpdater *DTU) {
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 (Use &Op : NewRet->operands()) {
Value *V = Op;
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);
Op = NewBC;
}
Instruction *NewEV = nullptr;
if (ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(V)) {
V = EVI->getOperand(0);
NewEV = EVI->clone();
if (NewBC) {
NewBC->setOperand(0, NewEV);
Pred->getInstList().insert(NewBC->getIterator(), NewEV);
} else {
Pred->getInstList().insert(NewRet->getIterator(), NewEV);
Op = NewEV;
}
}
if (PHINode *PN = dyn_cast<PHINode>(V)) {
if (PN->getParent() == BB) {
if (NewEV) {
NewEV->setOperand(0, PN->getIncomingValueForBlock(Pred));
} else if (NewBC)
NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
else
Op = 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();
if (DTU)
DTU->applyUpdates({{DominatorTree::Delete, Pred, BB}});
return cast<ReturnInst>(NewRet);
}
static Instruction *
SplitBlockAndInsertIfThenImpl(Value *Cond, Instruction *SplitBefore,
bool Unreachable, MDNode *BranchWeights,
DomTreeUpdater *DTU, DominatorTree *DT,
LoopInfo *LI, BasicBlock *ThenBlock) {
SmallVector<DominatorTree::UpdateType, 8> Updates;
BasicBlock *Head = SplitBefore->getParent();
BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
if (DTU) {
SmallSetVector<BasicBlock *, 8> UniqueSuccessorsOfHead(succ_begin(Tail),
succ_end(Tail));
Updates.push_back({DominatorTree::Insert, Head, Tail});
Updates.reserve(Updates.size() + 2 * UniqueSuccessorsOfHead.size());
for (BasicBlock *UniqueSuccessorOfHead : UniqueSuccessorsOfHead) {
Updates.push_back({DominatorTree::Insert, Tail, UniqueSuccessorOfHead});
Updates.push_back({DominatorTree::Delete, Head, UniqueSuccessorOfHead});
}
}
Instruction *HeadOldTerm = Head->getTerminator();
LLVMContext &C = Head->getContext();
Instruction *CheckTerm;
bool CreateThenBlock = (ThenBlock == nullptr);
if (CreateThenBlock) {
ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
if (Unreachable)
CheckTerm = new UnreachableInst(C, ThenBlock);
else {
CheckTerm = BranchInst::Create(Tail, ThenBlock);
if (DTU)
Updates.push_back({DominatorTree::Insert, ThenBlock, Tail});
}
CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
} else
CheckTerm = ThenBlock->getTerminator();
BranchInst *HeadNewTerm =
BranchInst::Create(/*ifTrue*/ ThenBlock, /*ifFalse*/ Tail, Cond);
if (DTU)
Updates.push_back({DominatorTree::Insert, Head, ThenBlock});
HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
if (DTU)
DTU->applyUpdates(Updates);
else if (DT) {
if (DomTreeNode *OldNode = DT->getNode(Head)) {
std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
for (DomTreeNode *Child : Children)
DT->changeImmediateDominator(Child, NewNode);
// Head dominates ThenBlock.
if (CreateThenBlock)
DT->addNewBlock(ThenBlock, Head);
else
DT->changeImmediateDominator(ThenBlock, Head);
}
}
if (LI) {
if (Loop *L = LI->getLoopFor(Head)) {
L->addBasicBlockToLoop(ThenBlock, *LI);
L->addBasicBlockToLoop(Tail, *LI);
}
}
return CheckTerm;
}
Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
Instruction *SplitBefore,
bool Unreachable,
MDNode *BranchWeights,
DominatorTree *DT, LoopInfo *LI,
BasicBlock *ThenBlock) {
return SplitBlockAndInsertIfThenImpl(Cond, SplitBefore, Unreachable,
BranchWeights,
/*DTU=*/nullptr, DT, LI, ThenBlock);
}
Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
Instruction *SplitBefore,
bool Unreachable,
MDNode *BranchWeights,
DomTreeUpdater *DTU, LoopInfo *LI,
BasicBlock *ThenBlock) {
return SplitBlockAndInsertIfThenImpl(Cond, SplitBefore, Unreachable,
BranchWeights, DTU, /*DT=*/nullptr, LI,
ThenBlock);
}
void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
Instruction **ThenTerm,
Instruction **ElseTerm,
MDNode *BranchWeights) {
BasicBlock *Head = SplitBefore->getParent();
BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
Instruction *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();
}
// After creating a control flow hub, the operands of PHINodes in an outgoing
// block Out no longer match the predecessors of that block. Predecessors of Out
// that are incoming blocks to the hub are now replaced by just one edge from
// the hub. To match this new control flow, the corresponding values from each
// PHINode must now be moved a new PHINode in the first guard block of the hub.
//
// This operation cannot be performed with SSAUpdater, because it involves one
// new use: If the block Out is in the list of Incoming blocks, then the newly
// created PHI in the Hub will use itself along that edge from Out to Hub.
static void reconnectPhis(BasicBlock *Out, BasicBlock *GuardBlock,
const SetVector<BasicBlock *> &Incoming,
BasicBlock *FirstGuardBlock) {
auto I = Out->begin();
while (I != Out->end() && isa<PHINode>(I)) {
auto Phi = cast<PHINode>(I);
auto NewPhi =
PHINode::Create(Phi->getType(), Incoming.size(),
Phi->getName() + ".moved", &FirstGuardBlock->back());
for (auto In : Incoming) {
Value *V = UndefValue::get(Phi->getType());
if (In == Out) {
V = NewPhi;
} else if (Phi->getBasicBlockIndex(In) != -1) {
V = Phi->removeIncomingValue(In, false);
}
NewPhi->addIncoming(V, In);
}
assert(NewPhi->getNumIncomingValues() == Incoming.size());
if (Phi->getNumOperands() == 0) {
Phi->replaceAllUsesWith(NewPhi);
I = Phi->eraseFromParent();
continue;
}
Phi->addIncoming(NewPhi, GuardBlock);
++I;
}
}
using BBPredicates = DenseMap<BasicBlock *, PHINode *>;
using BBSetVector = SetVector<BasicBlock *>;
// Redirects the terminator of the incoming block to the first guard
// block in the hub. The condition of the original terminator (if it
// was conditional) and its original successors are returned as a
// tuple <condition, succ0, succ1>. The function additionally filters
// out successors that are not in the set of outgoing blocks.
//
// - condition is non-null iff the branch is conditional.
// - Succ1 is non-null iff the sole/taken target is an outgoing block.
// - Succ2 is non-null iff condition is non-null and the fallthrough
// target is an outgoing block.
static std::tuple<Value *, BasicBlock *, BasicBlock *>
redirectToHub(BasicBlock *BB, BasicBlock *FirstGuardBlock,
const BBSetVector &Outgoing) {
auto Branch = cast<BranchInst>(BB->getTerminator());
auto Condition = Branch->isConditional() ? Branch->getCondition() : nullptr;
BasicBlock *Succ0 = Branch->getSuccessor(0);
BasicBlock *Succ1 = nullptr;
Succ0 = Outgoing.count(Succ0) ? Succ0 : nullptr;
if (Branch->isUnconditional()) {
Branch->setSuccessor(0, FirstGuardBlock);
assert(Succ0);
} else {
Succ1 = Branch->getSuccessor(1);
Succ1 = Outgoing.count(Succ1) ? Succ1 : nullptr;
assert(Succ0 || Succ1);
if (Succ0 && !Succ1) {
Branch->setSuccessor(0, FirstGuardBlock);
} else if (Succ1 && !Succ0) {
Branch->setSuccessor(1, FirstGuardBlock);
} else {
Branch->eraseFromParent();
BranchInst::Create(FirstGuardBlock, BB);
}
}
assert(Succ0 || Succ1);
return std::make_tuple(Condition, Succ0, Succ1);
}
// Capture the existing control flow as guard predicates, and redirect
// control flow from every incoming block to the first guard block in
// the hub.
//
// There is one guard predicate for each outgoing block OutBB. The
// predicate is a PHINode with one input for each InBB which
// represents whether the hub should transfer control flow to OutBB if
// it arrived from InBB. These predicates are NOT ORTHOGONAL. The Hub
// evaluates them in the same order as the Outgoing set-vector, and
// control branches to the first outgoing block whose predicate
// evaluates to true.
static void convertToGuardPredicates(
BasicBlock *FirstGuardBlock, BBPredicates &GuardPredicates,
SmallVectorImpl<WeakVH> &DeletionCandidates, const BBSetVector &Incoming,
const BBSetVector &Outgoing) {
auto &Context = Incoming.front()->getContext();
auto BoolTrue = ConstantInt::getTrue(Context);
auto BoolFalse = ConstantInt::getFalse(Context);
// The predicate for the last outgoing is trivially true, and so we
// process only the first N-1 successors.
for (int i = 0, e = Outgoing.size() - 1; i != e; ++i) {
auto Out = Outgoing[i];
LLVM_DEBUG(dbgs() << "Creating guard for " << Out->getName() << "\n");
auto Phi =
PHINode::Create(Type::getInt1Ty(Context), Incoming.size(),
StringRef("Guard.") + Out->getName(), FirstGuardBlock);
GuardPredicates[Out] = Phi;
}
for (auto In : Incoming) {
Value *Condition;
BasicBlock *Succ0;
BasicBlock *Succ1;
std::tie(Condition, Succ0, Succ1) =
redirectToHub(In, FirstGuardBlock, Outgoing);
// Optimization: Consider an incoming block A with both successors
// Succ0 and Succ1 in the set of outgoing blocks. The predicates
// for Succ0 and Succ1 complement each other. If Succ0 is visited
// first in the loop below, control will branch to Succ0 using the
// corresponding predicate. But if that branch is not taken, then
// control must reach Succ1, which means that the predicate for
// Succ1 is always true.
bool OneSuccessorDone = false;
for (int i = 0, e = Outgoing.size() - 1; i != e; ++i) {
auto Out = Outgoing[i];
auto Phi = GuardPredicates[Out];
if (Out != Succ0 && Out != Succ1) {
Phi->addIncoming(BoolFalse, In);
continue;
}
// Optimization: When only one successor is an outgoing block,
// the predicate is always true.
if (!Succ0 || !Succ1 || OneSuccessorDone) {
Phi->addIncoming(BoolTrue, In);
continue;
}
assert(Succ0 && Succ1);
OneSuccessorDone = true;
if (Out == Succ0) {
Phi->addIncoming(Condition, In);
continue;
}
auto Inverted = invertCondition(Condition);
DeletionCandidates.push_back(Condition);
Phi->addIncoming(Inverted, In);
}
}
}
// For each outgoing block OutBB, create a guard block in the Hub. The
// first guard block was already created outside, and available as the
// first element in the vector of guard blocks.
//
// Each guard block terminates in a conditional branch that transfers
// control to the corresponding outgoing block or the next guard
// block. The last guard block has two outgoing blocks as successors
// since the condition for the final outgoing block is trivially
// true. So we create one less block (including the first guard block)
// than the number of outgoing blocks.
static void createGuardBlocks(SmallVectorImpl<BasicBlock *> &GuardBlocks,
Function *F, const BBSetVector &Outgoing,
BBPredicates &GuardPredicates, StringRef Prefix) {
for (int i = 0, e = Outgoing.size() - 2; i != e; ++i) {
GuardBlocks.push_back(
BasicBlock::Create(F->getContext(), Prefix + ".guard", F));
}
assert(GuardBlocks.size() == GuardPredicates.size());
// To help keep the loop simple, temporarily append the last
// outgoing block to the list of guard blocks.
GuardBlocks.push_back(Outgoing.back());
for (int i = 0, e = GuardBlocks.size() - 1; i != e; ++i) {
auto Out = Outgoing[i];
assert(GuardPredicates.count(Out));
BranchInst::Create(Out, GuardBlocks[i + 1], GuardPredicates[Out],
GuardBlocks[i]);
}
// Remove the last block from the guard list.
GuardBlocks.pop_back();
}
BasicBlock *llvm::CreateControlFlowHub(
DomTreeUpdater *DTU, SmallVectorImpl<BasicBlock *> &GuardBlocks,
const BBSetVector &Incoming, const BBSetVector &Outgoing,
const StringRef Prefix) {
auto F = Incoming.front()->getParent();
auto FirstGuardBlock =
BasicBlock::Create(F->getContext(), Prefix + ".guard", F);
SmallVector<DominatorTree::UpdateType, 16> Updates;
if (DTU) {
for (auto In : Incoming) {
Updates.push_back({DominatorTree::Insert, In, FirstGuardBlock});
for (auto Succ : successors(In)) {
if (Outgoing.count(Succ))
Updates.push_back({DominatorTree::Delete, In, Succ});
}
}
}
BBPredicates GuardPredicates;
SmallVector<WeakVH, 8> DeletionCandidates;
convertToGuardPredicates(FirstGuardBlock, GuardPredicates, DeletionCandidates,
Incoming, Outgoing);
GuardBlocks.push_back(FirstGuardBlock);
createGuardBlocks(GuardBlocks, F, Outgoing, GuardPredicates, Prefix);
// Update the PHINodes in each outgoing block to match the new control flow.
for (int i = 0, e = GuardBlocks.size(); i != e; ++i) {
reconnectPhis(Outgoing[i], GuardBlocks[i], Incoming, FirstGuardBlock);
}
reconnectPhis(Outgoing.back(), GuardBlocks.back(), Incoming, FirstGuardBlock);
if (DTU) {
int NumGuards = GuardBlocks.size();
assert((int)Outgoing.size() == NumGuards + 1);
for (int i = 0; i != NumGuards - 1; ++i) {
Updates.push_back({DominatorTree::Insert, GuardBlocks[i], Outgoing[i]});
Updates.push_back(
{DominatorTree::Insert, GuardBlocks[i], GuardBlocks[i + 1]});
}
Updates.push_back({DominatorTree::Insert, GuardBlocks[NumGuards - 1],
Outgoing[NumGuards - 1]});
Updates.push_back({DominatorTree::Insert, GuardBlocks[NumGuards - 1],
Outgoing[NumGuards]});
DTU->applyUpdates(Updates);
}
for (auto I : DeletionCandidates) {
if (I->use_empty())
if (auto Inst = dyn_cast_or_null<Instruction>(I))
Inst->eraseFromParent();
}
return FirstGuardBlock;
}
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