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Remove the option to disable LazyValueInfo in JumpThreading, as it is now 

on by default and has received significant testing.

llvm-svn: 113852
This commit is contained in:
Owen Anderson 2010-09-14 20:57:41 +00:00
parent 7fc3f5d0f7
commit d361aac3d0
1 changed files with 38 additions and 111 deletions
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149
llvm/lib/Transforms/Scalar/JumpThreading.cpp
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@ -44,15 +44,6 @@ Threshold("jump-threading-threshold",
cl::desc("Max block size to duplicate for jump threading"),
cl::init(6), cl::Hidden);
// Turn on use of LazyValueInfo.
static cl::opt<bool>
EnableLVI("enable-jump-threading-lvi",
cl::desc("Use LVI for jump threading"),
cl::init(true),
cl::ReallyHidden);
namespace {
/// This pass performs 'jump threading', which looks at blocks that have
/// multiple predecessors and multiple successors. If one or more of the
@ -100,10 +91,8 @@ namespace {
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
if (EnableLVI) {
AU.addRequired<LazyValueInfo>();
AU.addPreserved<LazyValueInfo>();
}
AU.addRequired<LazyValueInfo>();
AU.addPreserved<LazyValueInfo>();
}
void FindLoopHeaders(Function &F);
@ -143,7 +132,7 @@ FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); }
bool JumpThreading::runOnFunction(Function &F) {
DEBUG(dbgs() << "Jump threading on function '" << F.getName() << "'\n");
TD = getAnalysisIfAvailable<TargetData>();
LVI = EnableLVI ? &getAnalysis<LazyValueInfo>() : 0;
LVI = &getAnalysis<LazyValueInfo>();
FindLoopHeaders(F);
@ -165,7 +154,7 @@ bool JumpThreading::runOnFunction(Function &F) {
DEBUG(dbgs() << " JT: Deleting dead block '" << BB->getName()
<< "' with terminator: " << *BB->getTerminator() << '\n');
LoopHeaders.erase(BB);
if (LVI) LVI->eraseBlock(BB);
LVI->eraseBlock(BB);
DeleteDeadBlock(BB);
Changed = true;
} else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
@ -190,7 +179,7 @@ bool JumpThreading::runOnFunction(Function &F) {
// for a block even if it doesn't get erased. This isn't totally
// awesome, but it allows us to use AssertingVH to prevent nasty
// dangling pointer issues within LazyValueInfo.
if (LVI) LVI->eraseBlock(BB);
LVI->eraseBlock(BB);
if (TryToSimplifyUncondBranchFromEmptyBlock(BB)) {
Changed = true;
// If we deleted BB and BB was the header of a loop, then the
@ -331,29 +320,25 @@ ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
/// TODO: Per PR2563, we could infer value range information about a
/// predecessor based on its terminator.
//
if (LVI) {
// FIXME: change this to use the more-rich 'getPredicateOnEdge' method if
// "I" is a non-local compare-with-a-constant instruction. This would be
// able to handle value inequalities better, for example if the compare is
// "X < 4" and "X < 3" is known true but "X < 4" itself is not available.
// Perhaps getConstantOnEdge should be smart enough to do this?
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
BasicBlock *P = *PI;
// If the value is known by LazyValueInfo to be a constant in a
// predecessor, use that information to try to thread this block.
Constant *PredCst = LVI->getConstantOnEdge(V, P, BB);
if (PredCst == 0 ||
(!isa<ConstantInt>(PredCst) && !isa<UndefValue>(PredCst)))
continue;
Result.push_back(std::make_pair(dyn_cast<ConstantInt>(PredCst), P));
}
return !Result.empty();
}
// FIXME: change this to use the more-rich 'getPredicateOnEdge' method if
// "I" is a non-local compare-with-a-constant instruction. This would be
// able to handle value inequalities better, for example if the compare is
// "X < 4" and "X < 3" is known true but "X < 4" itself is not available.
// Perhaps getConstantOnEdge should be smart enough to do this?
return false;
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
BasicBlock *P = *PI;
// If the value is known by LazyValueInfo to be a constant in a
// predecessor, use that information to try to thread this block.
Constant *PredCst = LVI->getConstantOnEdge(V, P, BB);
if (PredCst == 0 ||
(!isa<ConstantInt>(PredCst) && !isa<UndefValue>(PredCst)))
continue;
Result.push_back(std::make_pair(dyn_cast<ConstantInt>(PredCst), P));
}
return !Result.empty();
}
/// If I is a PHI node, then we know the incoming values for any constants.
@ -363,7 +348,7 @@ ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
if (isa<ConstantInt>(InVal) || isa<UndefValue>(InVal)) {
ConstantInt *CI = dyn_cast<ConstantInt>(InVal);
Result.push_back(std::make_pair(CI, PN->getIncomingBlock(i)));
} else if (LVI) {
} else {
Constant *CI = LVI->getConstantOnEdge(InVal,
PN->getIncomingBlock(i), BB);
// LVI returns null is no value could be determined.
@ -467,7 +452,7 @@ ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, TD);
if (Res == 0) {
if (!LVI || !isa<Constant>(RHS))
if (!isa<Constant>(RHS))
continue;
LazyValueInfo::Tristate
@ -488,8 +473,7 @@ ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
// If comparing a live-in value against a constant, see if we know the
// live-in value on any predecessors.
if (LVI && isa<Constant>(Cmp->getOperand(1)) &&
Cmp->getType()->isIntegerTy()) {
if (isa<Constant>(Cmp->getOperand(1)) && Cmp->getType()->isIntegerTy()) {
if (!isa<Instruction>(Cmp->getOperand(0)) ||
cast<Instruction>(Cmp->getOperand(0))->getParent() != BB) {
Constant *RHSCst = cast<Constant>(Cmp->getOperand(1));
@ -530,19 +514,15 @@ ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
}
}
if (LVI) {
// If all else fails, see if LVI can figure out a constant value for us.
Constant *CI = LVI->getConstant(V, BB);
ConstantInt *CInt = dyn_cast_or_null<ConstantInt>(CI);
if (CInt) {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
Result.push_back(std::make_pair(CInt, *PI));
}
return !Result.empty();
// If all else fails, see if LVI can figure out a constant value for us.
Constant *CI = LVI->getConstant(V, BB);
ConstantInt *CInt = dyn_cast_or_null<ConstantInt>(CI);
if (CInt) {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
Result.push_back(std::make_pair(CInt, *PI));
}
return false;
return !Result.empty();
}
@ -592,7 +572,7 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
// Remember if SinglePred was the entry block of the function. If so, we
// will need to move BB back to the entry position.
bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
if (LVI) LVI->eraseBlock(SinglePred);
LVI->eraseBlock(SinglePred);
MergeBasicBlockIntoOnlyPred(BB);
if (isEntry && BB != &BB->getParent()->getEntryBlock())
@ -645,75 +625,23 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
Instruction *CondInst = dyn_cast<Instruction>(Condition);
// If the condition is an instruction defined in another block, see if a
// predecessor has the same condition:
// br COND, BBX, BBY
// BBX:
// br COND, BBZ, BBW
if (!LVI &&
!Condition->hasOneUse() && // Multiple uses.
(CondInst == 0 || CondInst->getParent() != BB)) { // Non-local definition.
pred_iterator PI = pred_begin(BB), E = pred_end(BB);
if (isa<BranchInst>(BB->getTerminator())) {
for (; PI != E; ++PI) {
BasicBlock *P = *PI;
if (BranchInst *PBI = dyn_cast<BranchInst>(P->getTerminator()))
if (PBI->isConditional() && PBI->getCondition() == Condition &&
ProcessBranchOnDuplicateCond(P, BB))
return true;
}
} else {
assert(isa<SwitchInst>(BB->getTerminator()) && "Unknown jump terminator");
for (; PI != E; ++PI) {
BasicBlock *P = *PI;
if (SwitchInst *PSI = dyn_cast<SwitchInst>(P->getTerminator()))
if (PSI->getCondition() == Condition &&
ProcessSwitchOnDuplicateCond(P, BB))
return true;
}
}
}
// All the rest of our checks depend on the condition being an instruction.
if (CondInst == 0) {
// FIXME: Unify this with code below.
if (LVI && ProcessThreadableEdges(Condition, BB))
if (ProcessThreadableEdges(Condition, BB))
return true;
return false;
}
if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
if (!LVI &&
(!isa<PHINode>(CondCmp->getOperand(0)) ||
cast<PHINode>(CondCmp->getOperand(0))->getParent() != BB)) {
// If we have a comparison, loop over the predecessors to see if there is
// a condition with a lexically identical value.
pred_iterator PI = pred_begin(BB), E = pred_end(BB);
for (; PI != E; ++PI) {
BasicBlock *P = *PI;
if (BranchInst *PBI = dyn_cast<BranchInst>(P->getTerminator()))
if (PBI->isConditional() && P != BB) {
if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) {
if (CI->getOperand(0) == CondCmp->getOperand(0) &&
CI->getOperand(1) == CondCmp->getOperand(1) &&
CI->getPredicate() == CondCmp->getPredicate()) {
// TODO: Could handle things like (x != 4) --> (x == 17)
if (ProcessBranchOnDuplicateCond(P, BB))
return true;
}
}
}
}
}
// For a comparison where the LHS is outside this block, it's possible
// that we've branched on it before. Used LVI to see if we can simplify
// the branch based on that.
BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
if (LVI && CondBr && CondConst && CondBr->isConditional() && PI != PE &&
if (CondBr && CondConst && CondBr->isConditional() && PI != PE &&
(!isa<Instruction>(CondCmp->getOperand(0)) ||
cast<Instruction>(CondCmp->getOperand(0))->getParent() != BB)) {
// For predecessor edge, determine if the comparison is true or false
@ -1455,8 +1383,7 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB,
<< ", across block:\n "
<< *BB << "\n");
if (LVI)
LVI->threadEdge(PredBB, BB, SuccBB);
LVI->threadEdge(PredBB, BB, SuccBB);
// We are going to have to map operands from the original BB block to the new
// copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to