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Remove functions from the FnSet when one of their callee's is being merged. This

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maintains the guarantee that the DenseSet expects two elements it contains to
not go from inequal to equal under its nose.

As a side-effect, this also lets us switch from iterating to a fixed-point to
actually maintaining a work queue of functions to look at again, and we don't
add thunks to our work queue so we don't need to detect and ignore them.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122677 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2011-01-02 02:46:33 +00:00
parent 15df04472a
commit abd6c75409
1 changed files with 66 additions and 82 deletions
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148
lib/Transforms/IPO/MergeFunctions.cpp
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@ -160,20 +160,36 @@ public:
private:
typedef DenseSet<ComparableFunction> FnSetType;
/// A work queue of functions that may have been modified and should be
/// analyzed again.
std::vector<WeakVH> Deferred;
/// Insert a ComparableFunction into the FnSet, or merge it away if it's
/// equal to one that's already present.
bool Insert(FnSetType &FnSet, ComparableFunction &NewF);
bool Insert(ComparableFunction &NewF);
/// Remove a Function from the FnSet and queue it up for a second sweep of
/// analysis.
void Remove(Function *F);
/// Find the functions that use this Value and remove them from FnSet and
/// queue the functions.
void RemoveUsers(Value *V);
/// MergeTwoFunctions - Merge two equivalent functions. Upon completion, G
/// may be deleted, or may be converted into a thunk. In either case, it
/// should never be visited again.
void MergeTwoFunctions(Function *F, Function *G) const;
void MergeTwoFunctions(Function *F, Function *G);
/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also
/// replace direct uses of G with bitcast(F). Deletes G.
void WriteThunk(Function *F, Function *G) const;
void WriteThunk(Function *F, Function *G);
/// The set of all distinct functions. Use the Insert and Remove methods to
/// modify it.
FnSetType FnSet;
/// TargetData for more accurate GEP comparisons. May be NULL.
TargetData *TD;
};
@ -560,7 +576,7 @@ bool FunctionComparator::Compare() {
/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also replace
/// direct uses of G with bitcast(F). Deletes G.
void MergeFunctions::WriteThunk(Function *F, Function *G) const {
void MergeFunctions::WriteThunk(Function *F, Function *G) {
if (!G->mayBeOverridden()) {
// Redirect direct callers of G to F.
Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
@ -569,10 +585,12 @@ void MergeFunctions::WriteThunk(Function *F, Function *G) const {
Value::use_iterator TheIter = UI;
++UI;
CallSite CS(*TheIter);
if (CS && CS.isCallee(TheIter))
if (CS && CS.isCallee(TheIter)) {
Remove(CS.getInstruction()->getParent()->getParent());
TheIter.getUse().set(BitcastF);
}
}
}
// If G was internal then we may have replaced all uses of G with F. If so,
// stop here and delete G. There's no need for a thunk.
@ -606,6 +624,7 @@ void MergeFunctions::WriteThunk(Function *F, Function *G) const {
NewG->copyAttributesFrom(G);
NewG->takeName(G);
RemoveUsers(G);
G->replaceAllUsesWith(NewG);
G->eraseFromParent();
@ -615,7 +634,7 @@ void MergeFunctions::WriteThunk(Function *F, Function *G) const {
/// MergeTwoFunctions - Merge two equivalent functions. Upon completion,
/// Function G is deleted.
void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) const {
void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) {
if (F->mayBeOverridden()) {
assert(G->mayBeOverridden());
@ -624,6 +643,7 @@ void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) const {
F->getParent());
H->copyAttributesFrom(F);
H->takeName(F);
RemoveUsers(F);
F->replaceAllUsesWith(H);
unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
@ -632,7 +652,7 @@ void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) const {
WriteThunk(F, H);
F->setAlignment(MaxAlignment);
F->setLinkage(GlobalValue::InternalLinkage);
F->setLinkage(GlobalValue::PrivateLinkage);
++NumDoubleWeak;
} else {
@ -644,7 +664,7 @@ void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) const {
// Insert - Insert a ComparableFunction into the FnSet, or merge it away if
// equal to one that's already inserted.
bool MergeFunctions::Insert(FnSetType &FnSet, ComparableFunction &NewF) {
bool MergeFunctions::Insert(ComparableFunction &NewF) {
std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF);
if (Result.second)
return false;
@ -664,91 +684,52 @@ bool MergeFunctions::Insert(FnSetType &FnSet, ComparableFunction &NewF) {
return true;
}
// IsThunk - This method determines whether or not a given Function is a thunk\// like the ones emitted by this pass and therefore not subject to further
// merging.
static bool IsThunk(const Function *F) {
// The safe direction to fail is to return true. In that case, the function
// will be removed from merging analysis. If we failed to including functions
// then we may try to merge unmergable thing (ie., identical weak functions)
// which will push us into an infinite loop.
assert(!F->isDeclaration() && "Expected a function definition.");
const BasicBlock *BB = &F->front();
// A thunk is:
// bitcast-inst*
// optional-reg tail call @thunkee(args...*)
// ret void|optional-reg
// where the args are in the same order as the arguments.
// Put this at the top since it triggers most often.
const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
if (!RI) return false;
// Verify that the sequence of bitcast-inst's are all casts of arguments and
// that there aren't any extras (ie. no repeated casts).
int LastArgNo = -1;
BasicBlock::const_iterator I = BB->begin();
while (const BitCastInst *BCI = dyn_cast<BitCastInst>(I)) {
const Argument *A = dyn_cast<Argument>(BCI->getOperand(0));
if (!A) return false;
if ((int)A->getArgNo() <= LastArgNo) return false;
LastArgNo = A->getArgNo();
++I;
// Remove - Remove a function from FnSet. If it was already in FnSet, add it to
// Deferred so that we'll look at it in the next round.
void MergeFunctions::Remove(Function *F) {
ComparableFunction CF = ComparableFunction(F, TD);
if (FnSet.erase(CF)) {
Deferred.push_back(F);
}
}
// Verify that we have a direct tail call and that the calling conventions
// and number of arguments match.
const CallInst *CI = dyn_cast<CallInst>(I++);
if (!CI || !CI->isTailCall() || !CI->getCalledFunction() ||
CI->getCallingConv() != CI->getCalledFunction()->getCallingConv() ||
CI->getNumArgOperands() != F->arg_size())
return false;
// Verify that the call instruction has the same arguments as this function
// and that they're all either the incoming argument or a cast of the right
// argument.
for (unsigned i = 0, e = CI->getNumArgOperands(); i != e; ++i) {
const Value *V = CI->getArgOperand(i);
const Argument *A = dyn_cast<Argument>(V);
if (!A) {
const BitCastInst *BCI = dyn_cast<BitCastInst>(V);
if (!BCI) return false;
A = cast<Argument>(BCI->getOperand(0));
// RemoveUsers - For each instruction used by the value, Remove() the function
// that contains the instruction. This should happen right before a call to RAUW.
void MergeFunctions::RemoveUsers(Value *V) {
for (Value::use_iterator UI = V->use_begin(), UE = V->use_end();
UI != UE; ++UI) {
Use &U = UI.getUse();
if (Instruction *I = dyn_cast<Instruction>(U.getUser())) {
Remove(I->getParent()->getParent());
}
if (A->getArgNo() != i) return false;
}
// Verify that the terminator is a ret void (if we're void) or a ret of the
// call's return, or a ret of a bitcast of the call's return.
if (const BitCastInst *BCI = dyn_cast<BitCastInst>(I)) {
++I;
if (BCI->getOperand(0) != CI) return false;
}
if (RI != I) return false;
if (RI->getNumOperands() == 0)
return CI->getType()->isVoidTy();
return RI->getReturnValue() == CI;
}
bool MergeFunctions::runOnModule(Module &M) {
bool Changed = false;
TD = getAnalysisIfAvailable<TargetData>();
bool LocalChanged;
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
Deferred.push_back(WeakVH(I));
}
do {
std::vector<WeakVH> Worklist;
Deferred.swap(Worklist);
DEBUG(dbgs() << "size of module: " << M.size() << '\n');
LocalChanged = false;
FnSetType FnSet;
DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n');
// Insert only strong functions and merge them. Strong function merging
// always deletes one of them.
for (Module::iterator I = M.begin(), E = M.end(); I != E;) {
Function *F = I++;
for (std::vector<WeakVH>::iterator I = Worklist.begin(),
E = Worklist.end(); I != E; ++I) {
if (!*I) continue;
Function *F = cast<Function>(*I);
if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
!F->mayBeOverridden() && !IsThunk(F)) {
!F->mayBeOverridden()) {
ComparableFunction CF = ComparableFunction(F, TD);
LocalChanged |= Insert(FnSet, CF);
Changed |= Insert(CF);
}
}
@ -756,17 +737,20 @@ bool MergeFunctions::runOnModule(Module &M) {
// create thunks to the strong function when possible. When two weak
// functions are identical, we create a new strong function with two weak
// weak thunks to it which are identical but not mergable.
for (Module::iterator I = M.begin(), E = M.end(); I != E;) {
Function *F = I++;
for (std::vector<WeakVH>::iterator I = Worklist.begin(),
E = Worklist.end(); I != E; ++I) {
if (!*I) continue;
Function *F = cast<Function>(*I);
if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
F->mayBeOverridden() && !IsThunk(F)) {
F->mayBeOverridden()) {
ComparableFunction CF = ComparableFunction(F, TD);
LocalChanged |= Insert(FnSet, CF);
Changed |= Insert(CF);
}
}
DEBUG(dbgs() << "size of FnSet: " << FnSet.size() << '\n');
Changed |= LocalChanged;
} while (LocalChanged);
} while (!Deferred.empty());
FnSet.clear();
return Changed;
}