Fix many bugs when merging weak-strong and weak-weak pairs. We now merge all

strong functions first to make sure they're the canonical definitions and then
do a second pass looking only for weak functions.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@113104 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2010-09-05 08:22:49 +00:00
parent beac75da37
commit b0104e1bb5

View File

@ -69,32 +69,79 @@ using namespace llvm;
STATISTIC(NumFunctionsMerged, "Number of functions merged");
namespace {
/// MergeFunctions finds functions which will generate identical machine code,
/// by considering all pointer types to be equivalent. Once identified,
/// MergeFunctions will fold them by replacing a call to one to a call to a
/// bitcast of the other.
///
class MergeFunctions : public ModulePass {
public:
static char ID;
MergeFunctions() : ModulePass(ID) {}
bool runOnModule(Module &M);
static unsigned ProfileFunction(const Function *F) {
const FunctionType *FTy = F->getFunctionType();
private:
/// 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;
/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also
/// replace direct uses of G with bitcast(F).
void WriteThunk(Function *F, Function *G) const;
TargetData *TD;
};
FoldingSetNodeID ID;
ID.AddInteger(F->size());
ID.AddInteger(F->getCallingConv());
ID.AddBoolean(F->hasGC());
ID.AddBoolean(FTy->isVarArg());
ID.AddInteger(FTy->getReturnType()->getTypeID());
for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
ID.AddInteger(FTy->getParamType(i)->getTypeID());
return ID.ComputeHash();
}
class ComparableFunction {
public:
ComparableFunction(Function *Func, TargetData *TD)
: Func(Func), Hash(ProfileFunction(Func)), TD(TD) {}
AssertingVH<Function> const Func;
const unsigned Hash;
TargetData * const TD;
};
struct MergeFunctionsEqualityInfo {
static ComparableFunction *getEmptyKey() {
return reinterpret_cast<ComparableFunction*>(0);
}
static ComparableFunction *getTombstoneKey() {
return reinterpret_cast<ComparableFunction*>(-1);
}
static unsigned getHashValue(const ComparableFunction *CF) {
return CF->Hash;
}
static bool isEqual(const ComparableFunction *LHS,
const ComparableFunction *RHS);
};
/// MergeFunctions finds functions which will generate identical machine code,
/// by considering all pointer types to be equivalent. Once identified,
/// MergeFunctions will fold them by replacing a call to one to a call to a
/// bitcast of the other.
///
class MergeFunctions : public ModulePass {
public:
static char ID;
MergeFunctions() : ModulePass(ID) {}
bool runOnModule(Module &M);
private:
typedef DenseSet<ComparableFunction *, MergeFunctionsEqualityInfo> FnSetType;
/// 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);
/// 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;
/// 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;
TargetData *TD;
};
} // end anonymous namespace
char MergeFunctions::ID = 0;
INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false);
@ -475,7 +522,7 @@ bool FunctionComparator::Compare() {
}
/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also replace
/// direct uses of G with bitcast(F).
/// direct uses of G with bitcast(F). Deletes G.
void MergeFunctions::WriteThunk(Function *F, Function *G) const {
if (!G->mayBeOverridden()) {
// Redirect direct callers of G to F.
@ -553,100 +600,138 @@ void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) const {
++NumFunctionsMerged;
}
static unsigned ProfileFunction(const Function *F) {
const FunctionType *FTy = F->getFunctionType();
// 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) {
std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF);
if (Result.second)
return false;
FoldingSetNodeID ID;
ID.AddInteger(F->size());
ID.AddInteger(F->getCallingConv());
ID.AddBoolean(F->hasGC());
ID.AddBoolean(FTy->isVarArg());
ID.AddInteger(FTy->getReturnType()->getTypeID());
for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
ID.AddInteger(FTy->getParamType(i)->getTypeID());
return ID.ComputeHash();
ComparableFunction *OldF = *Result.first;
assert(OldF && "Expected a hash collision");
// Never thunk a strong function to a weak function.
assert(!OldF->Func->isWeakForLinker() || NewF->Func->isWeakForLinker());
DEBUG(dbgs() << " " << OldF->Func->getName() << " == "
<< NewF->Func->getName() << '\n');
Function *DeleteF = NewF->Func;
delete NewF;
MergeTwoFunctions(OldF->Func, DeleteF);
return true;
}
class ComparableFunction {
public:
ComparableFunction(Function *Func, TargetData *TD)
: Func(Func), Hash(ProfileFunction(Func)), TD(TD) {}
// 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.
AssertingVH<Function> const Func;
const unsigned Hash;
TargetData * const TD;
};
if (F->size() != 1)
return false;
struct MergeFunctionsEqualityInfo {
static ComparableFunction *getEmptyKey() {
return reinterpret_cast<ComparableFunction*>(0);
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.
// 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;
}
static ComparableFunction *getTombstoneKey() {
return reinterpret_cast<ComparableFunction*>(-1);
// 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.
const CallInst *CI = dyn_cast<CallInst>(I++);
if (!CI || !CI->isTailCall() ||
CI->getNumArgOperands() != F->arg_size()) return false;
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));
}
if (A->getArgNo() != i) return false;
}
static unsigned getHashValue(const ComparableFunction *CF) {
return CF->Hash;
// 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.
const Value *RetOp = CI;
if (const BitCastInst *BCI = dyn_cast<BitCastInst>(I)) {
++I;
if (BCI->getOperand(0) != CI) return false;
RetOp = BCI;
}
static bool isEqual(const ComparableFunction *LHS,
const ComparableFunction *RHS) {
if (LHS == RHS)
return true;
if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
RHS == getEmptyKey() || RHS == getTombstoneKey())
return false;
assert(LHS->TD == RHS->TD && "Comparing functions for different targets");
return FunctionComparator(LHS->TD, LHS->Func, RHS->Func).Compare();
}
};
const ReturnInst *RI = dyn_cast<ReturnInst>(I);
if (!RI) return false;
if (RI->getNumOperands() == 0)
return CI->getType()->isVoidTy();
return RI->getReturnValue() == CI;
}
bool MergeFunctions::runOnModule(Module &M) {
typedef DenseSet<ComparableFunction *, MergeFunctionsEqualityInfo> FnSetType;
bool Changed = false;
TD = getAnalysisIfAvailable<TargetData>();
std::vector<Function *> Funcs;
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage())
Funcs.push_back(F);
}
bool LocalChanged;
do {
DEBUG(dbgs() << "size: " << M.size() << '\n');
LocalChanged = false;
FnSetType FnSet;
for (unsigned i = 0, e = Funcs.size(); i != e;) {
Function *F = Funcs[i];
ComparableFunction *NewF = new ComparableFunction(F, TD);
std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF);
if (!Result.second) {
ComparableFunction *&OldF = *Result.first;
assert(OldF && "Expected a hash collision");
// NewF will be deleted in favour of OldF unless NewF is strong and
// OldF is weak in which case swap them to keep the strong definition.
// 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++;
if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
!F->isWeakForLinker() && !IsThunk(F)) {
ComparableFunction *CF = new ComparableFunction(F, TD);
LocalChanged |= Insert(FnSet, CF);
}
}
if (OldF->Func->isWeakForLinker() && !NewF->Func->isWeakForLinker())
std::swap(OldF, NewF);
DEBUG(dbgs() << " " << OldF->Func->getName() << " == "
<< NewF->Func->getName() << '\n');
Funcs.erase(Funcs.begin() + i);
--e;
Function *DeleteF = NewF->Func;
delete NewF;
MergeTwoFunctions(OldF->Func, DeleteF);
LocalChanged = true;
Changed = true;
} else {
++i;
// Insert only weak functions and merge them. By doing these second we
// 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++;
if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
F->isWeakForLinker() && !IsThunk(F)) {
ComparableFunction *CF = new ComparableFunction(F, TD);
LocalChanged |= Insert(FnSet, CF);
}
}
DeleteContainerPointers(FnSet);
Changed |= LocalChanged;
} while (LocalChanged);
return Changed;
}
bool MergeFunctionsEqualityInfo::isEqual(const ComparableFunction *LHS,
const ComparableFunction *RHS) {
if (LHS == RHS)
return true;
if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
RHS == getEmptyKey() || RHS == getTombstoneKey())
return false;
assert(LHS->TD == RHS->TD && "Comparing functions for different targets");
return FunctionComparator(LHS->TD, LHS->Func, RHS->Func).Compare();
}