void LLVM_General_GetSwitchCases(
LLVMValueRef v,
LLVMValueRef *values,
LLVMBasicBlockRef *dests
) {
SwitchInst *s = unwrap<SwitchInst>(v);
for(SwitchInst::CaseIt i = s->case_begin(); i != s->case_end(); ++i, ++values, ++dests) {
*values = wrap(i.getCaseValue());
*dests = wrap(i.getCaseSuccessor());
}
}
// processSwitchInst - Replace the specified switch instruction with a sequence
// of chained if-then instructions.
//
void LowerSwitchPass::processSwitchInst(SwitchInst *SI) {
BasicBlock *origBlock = SI->getParent();
BasicBlock *defaultBlock = SI->getDefaultDest();
Function *F = origBlock->getParent();
Value *switchValue = SI->getCondition();
// Create a new, empty default block so that the new hierarchy of
// if-then statements go to this and the PHI nodes are happy.
BasicBlock* newDefault = BasicBlock::Create(getGlobalContext(), "newDefault");
#if LLVM_VERSION_CODE >= LLVM_VERSION(3, 8)
F->getBasicBlockList().insert(defaultBlock->getIterator(), newDefault);
#else
F->getBasicBlockList().insert(defaultBlock, newDefault);
#endif
BranchInst::Create(defaultBlock, newDefault);
// If there is an entry in any PHI nodes for the default edge, make sure
// to update them as well.
for (BasicBlock::iterator I = defaultBlock->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
int BlockIdx = PN->getBasicBlockIndex(origBlock);
assert(BlockIdx != -1 && "Switch didn't go to this successor??");
PN->setIncomingBlock((unsigned)BlockIdx, newDefault);
}
CaseVector cases;
#if LLVM_VERSION_CODE >= LLVM_VERSION(3, 1)
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
cases.push_back(SwitchCase(i.getCaseValue(),
i.getCaseSuccessor()));
#else
for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
cases.push_back(SwitchCase(SI->getSuccessorValue(i),
SI->getSuccessor(i)));
#endif
// reverse cases, as switchConvert constructs a chain of
// basic blocks by appending to the front. if we reverse,
// the if comparisons will happen in the same order
// as the cases appear in the switch
std::reverse(cases.begin(), cases.end());
switchConvert(cases.begin(), cases.end(), switchValue, origBlock, newDefault);
// We are now done with the switch instruction, so delete it
origBlock->getInstList().erase(SI);
}
/// processSwitch - Simplify a switch instruction by removing cases which can
/// never fire. If the uselessness of a case could be determined locally then
/// constant propagation would already have figured it out. Instead, walk the
/// predecessors and statically evaluate cases based on information available
/// on that edge. Cases that cannot fire no matter what the incoming edge can
/// safely be removed. If a case fires on every incoming edge then the entire
/// switch can be removed and replaced with a branch to the case destination.
bool CorrelatedValuePropagation::processSwitch(SwitchInst *SI) {
Value *Cond = SI->getCondition();
BasicBlock *BB = SI->getParent();
// If the condition was defined in same block as the switch then LazyValueInfo
// currently won't say anything useful about it, though in theory it could.
if (isa<Instruction>(Cond) && cast<Instruction>(Cond)->getParent() == BB)
return false;
// If the switch is unreachable then trying to improve it is a waste of time.
pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
if (PB == PE) return false;
// Analyse each switch case in turn. This is done in reverse order so that
// removing a case doesn't cause trouble for the iteration.
bool Changed = false;
for (SwitchInst::CaseIt CI = SI->case_end(), CE = SI->case_begin(); CI-- != CE;
) {
ConstantInt *Case = CI.getCaseValue();
// Check to see if the switch condition is equal to/not equal to the case
// value on every incoming edge, equal/not equal being the same each time.
LazyValueInfo::Tristate State = LazyValueInfo::Unknown;
for (pred_iterator PI = PB; PI != PE; ++PI) {
// Is the switch condition equal to the case value?
LazyValueInfo::Tristate Value = LVI->getPredicateOnEdge(CmpInst::ICMP_EQ,
Cond, Case, *PI,
BB, SI);
// Give up on this case if nothing is known.
if (Value == LazyValueInfo::Unknown) {
State = LazyValueInfo::Unknown;
break;
}
// If this was the first edge to be visited, record that all other edges
// need to give the same result.
if (PI == PB) {
State = Value;
continue;
}
// If this case is known to fire for some edges and known not to fire for
// others then there is nothing we can do - give up.
if (Value != State) {
State = LazyValueInfo::Unknown;
break;
}
}
if (State == LazyValueInfo::False) {
// This case never fires - remove it.
CI.getCaseSuccessor()->removePredecessor(BB);
SI->removeCase(CI); // Does not invalidate the iterator.
// The condition can be modified by removePredecessor's PHI simplification
// logic.
Cond = SI->getCondition();
++NumDeadCases;
Changed = true;
} else if (State == LazyValueInfo::True) {
// This case always fires. Arrange for the switch to be turned into an
// unconditional branch by replacing the switch condition with the case
// value.
SI->setCondition(Case);
NumDeadCases += SI->getNumCases();
Changed = true;
break;
}
}
if (Changed)
// If the switch has been simplified to the point where it can be replaced
// by a branch then do so now.
ConstantFoldTerminator(BB);
return Changed;
}
/// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
/// Val is not constrained on the edge.
static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
BasicBlock *BBTo, LVILatticeVal &Result) {
// TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
// know that v != 0.
if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
// If this is a conditional branch and only one successor goes to BBTo, then
// we maybe able to infer something from the condition.
if (BI->isConditional() &&
BI->getSuccessor(0) != BI->getSuccessor(1)) {
bool isTrueDest = BI->getSuccessor(0) == BBTo;
assert(BI->getSuccessor(!isTrueDest) == BBTo &&
"BBTo isn't a successor of BBFrom");
// If V is the condition of the branch itself, then we know exactly what
// it is.
if (BI->getCondition() == Val) {
Result = LVILatticeVal::get(ConstantInt::get(
Type::getInt1Ty(Val->getContext()), isTrueDest));
return true;
}
// If the condition of the branch is an equality comparison, we may be
// able to infer the value.
ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
if (ICI && isa<Constant>(ICI->getOperand(1))) {
if (ICI->isEquality() && ICI->getOperand(0) == Val) {
// We know that V has the RHS constant if this is a true SETEQ or
// false SETNE.
if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
else
Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
return true;
}
// Recognize the range checking idiom that InstCombine produces.
// (X-C1) u< C2 --> [C1, C1+C2)
ConstantInt *NegOffset = 0;
if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
match(ICI->getOperand(0), m_Add(m_Specific(Val),
m_ConstantInt(NegOffset)));
ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
// Calculate the range of values that would satisfy the comparison.
ConstantRange CmpRange(CI->getValue());
ConstantRange TrueValues =
ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
if (NegOffset) // Apply the offset from above.
TrueValues = TrueValues.subtract(NegOffset->getValue());
// If we're interested in the false dest, invert the condition.
if (!isTrueDest) TrueValues = TrueValues.inverse();
Result = LVILatticeVal::getRange(TrueValues);
return true;
}
}
}
}
// If the edge was formed by a switch on the value, then we may know exactly
// what it is.
if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
if (SI->getCondition() != Val)
return false;
bool DefaultCase = SI->getDefaultDest() == BBTo;
unsigned BitWidth = Val->getType()->getIntegerBitWidth();
ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
i != e; ++i) {
ConstantRange EdgeVal(i.getCaseValue()->getValue());
if (DefaultCase) {
// It is possible that the default destination is the destination of
// some cases. There is no need to perform difference for those cases.
if (i.getCaseSuccessor() != BBTo)
EdgesVals = EdgesVals.difference(EdgeVal);
} else if (i.getCaseSuccessor() == BBTo)
EdgesVals = EdgesVals.unionWith(EdgeVal);
}
Result = LVILatticeVal::getRange(EdgesVals);
return true;
}
return false;
}
/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
/// trivial: that is, that the condition controls whether or not the loop does
/// anything at all. If this is a trivial condition, unswitching produces no
/// code duplications (equivalently, it produces a simpler loop and a new empty
/// loop, which gets deleted).
///
/// If this is a trivial condition, return true, otherwise return false. When
/// returning true, this sets Cond and Val to the condition that controls the
/// trivial condition: when Cond dynamically equals Val, the loop is known to
/// exit. Finally, this sets LoopExit to the BB that the loop exits to when
/// Cond == Val.
///
bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
BasicBlock **LoopExit) {
BasicBlock *Header = currentLoop->getHeader();
TerminatorInst *HeaderTerm = Header->getTerminator();
LLVMContext &Context = Header->getContext();
BasicBlock *LoopExitBB = 0;
if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
// If the header block doesn't end with a conditional branch on Cond, we
// can't handle it.
if (!BI->isConditional() || BI->getCondition() != Cond)
return false;
// Check to see if a successor of the branch is guaranteed to
// exit through a unique exit block without having any
// side-effects. If so, determine the value of Cond that causes it to do
// this.
if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
BI->getSuccessor(0)))) {
if (Val) *Val = ConstantInt::getTrue(Context);
} else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
BI->getSuccessor(1)))) {
if (Val) *Val = ConstantInt::getFalse(Context);
}
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
// If this isn't a switch on Cond, we can't handle it.
if (SI->getCondition() != Cond) return false;
// Check to see if a successor of the switch is guaranteed to go to the
// latch block or exit through a one exit block without having any
// side-effects. If so, determine the value of Cond that causes it to do
// this.
// Note that we can't trivially unswitch on the default case or
// on already unswitched cases.
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
i != e; ++i) {
BasicBlock* LoopExitCandidate;
if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
i.getCaseSuccessor()))) {
// Okay, we found a trivial case, remember the value that is trivial.
ConstantInt* CaseVal = i.getCaseValue();
// Check that it was not unswitched before, since already unswitched
// trivial vals are looks trivial too.
if (BranchesInfo.isUnswitched(SI, CaseVal))
continue;
LoopExitBB = LoopExitCandidate;
if (Val) *Val = CaseVal;
break;
}
}
}
// If we didn't find a single unique LoopExit block, or if the loop exit block
// contains phi nodes, this isn't trivial.
if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
return false; // Can't handle this.
if (LoopExit) *LoopExit = LoopExitBB;
// We already know that nothing uses any scalar values defined inside of this
// loop. As such, we just have to check to see if this loop will execute any
// side-effecting instructions (e.g. stores, calls, volatile loads) in the
// part of the loop that the code *would* execute. We already checked the
// tail, check the header now.
for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
if (I->mayHaveSideEffects())
return false;
return true;
}
/// processCurrentLoop - Do actual work and unswitch loop if possible
/// and profitable.
bool LoopUnswitch::processCurrentLoop() {
bool Changed = false;
initLoopData();
// If LoopSimplify was unable to form a preheader, don't do any unswitching.
if (!loopPreheader)
return false;
// Loops with indirectbr cannot be cloned.
if (!currentLoop->isSafeToClone())
return false;
// Without dedicated exits, splitting the exit edge may fail.
if (!currentLoop->hasDedicatedExits())
return false;
LLVMContext &Context = loopHeader->getContext();
// Probably we reach the quota of branches for this loop. If so
// stop unswitching.
if (!BranchesInfo.countLoop(currentLoop))
return false;
// Loop over all of the basic blocks in the loop. If we find an interior
// block that is branching on a loop-invariant condition, we can unswitch this
// loop.
for (Loop::block_iterator I = currentLoop->block_begin(),
E = currentLoop->block_end(); I != E; ++I) {
TerminatorInst *TI = (*I)->getTerminator();
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
// If this isn't branching on an invariant condition, we can't unswitch
// it.
if (BI->isConditional()) {
// See if this, or some part of it, is loop invariant. If so, we can
// unswitch on it if we desire.
Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
currentLoop, Changed);
if (LoopCond && UnswitchIfProfitable(LoopCond,
ConstantInt::getTrue(Context))) {
++NumBranches;
return true;
}
}
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
currentLoop, Changed);
unsigned NumCases = SI->getNumCases();
if (LoopCond && NumCases) {
// Find a value to unswitch on:
// FIXME: this should chose the most expensive case!
// FIXME: scan for a case with a non-critical edge?
Constant *UnswitchVal = NULL;
// Do not process same value again and again.
// At this point we have some cases already unswitched and
// some not yet unswitched. Let's find the first not yet unswitched one.
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
i != e; ++i) {
Constant* UnswitchValCandidate = i.getCaseValue();
if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
UnswitchVal = UnswitchValCandidate;
break;
}
}
if (!UnswitchVal)
continue;
if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
++NumSwitches;
return true;
}
}
}
// Scan the instructions to check for unswitchable values.
for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
BBI != E; ++BBI)
if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
currentLoop, Changed);
if (LoopCond && UnswitchIfProfitable(LoopCond,
ConstantInt::getTrue(Context))) {
++NumSelects;
return true;
}
}
}
return Changed;
}
