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Fix major bug in thunk detection. Also verify the calling convention.

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Switch from isWeakForLinker to mayBeOverridden which is more accurate.

Add more statistics and debugging info. Add comments. Move static function
outside anonymous namespace.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@113190 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2010-09-07 01:42:10 +00:00
parent e9e0fc5eed
commit 2b6c01b40b
1 changed files with 39 additions and 22 deletions
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61
lib/Transforms/IPO/MergeFunctions.cpp
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@ -67,9 +67,12 @@
using namespace llvm;
STATISTIC(NumFunctionsMerged, "Number of functions merged");
STATISTIC(NumThunksWritten, "Number of thunks generated");
STATISTIC(NumDoubleWeak, "Number of new functions created");
namespace {
/// ProfileFunction - Creates a hash-code for the function which is the same
/// for any two functions that will compare equal, without looking at the
/// instructions inside the function.
static unsigned ProfileFunction(const Function *F) {
const FunctionType *FTy = F->getFunctionType();
@ -84,6 +87,8 @@ static unsigned ProfileFunction(const Function *F) {
return ID.ComputeHash();
}
namespace {
class ComparableFunction {
public:
static const ComparableFunction EmptyKey;
@ -117,7 +122,7 @@ const ComparableFunction ComparableFunction::EmptyKey = ComparableFunction(0);
const ComparableFunction ComparableFunction::TombstoneKey =
ComparableFunction(1);
} // anonymous namespace
}
namespace llvm {
template <>
@ -508,14 +513,14 @@ bool FunctionComparator::Compare() {
return false;
assert(F1->arg_size() == F2->arg_size() &&
"Identical functions have a different number of args.");
"Identically typed functions have different numbers of args!");
// Visit the arguments so that they get enumerated in the order they're
// passed in.
for (Function::const_arg_iterator f1i = F1->arg_begin(),
f2i = F2->arg_begin(), f1e = F1->arg_end(); f1i != f1e; ++f1i, ++f2i) {
if (!Enumerate(f1i, f2i))
llvm_unreachable("Arguments repeat");
llvm_unreachable("Arguments repeat!");
}
// We do a CFG-ordered walk since the actual ordering of the blocks in the
@ -567,7 +572,7 @@ void MergeFunctions::WriteThunk(Function *F, Function *G) const {
}
}
// If G was internal then we may have replaced all uses if G with F. If so,
// 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.
if (G->hasLocalLinkage() && G->use_empty()) {
G->eraseFromParent();
@ -601,13 +606,16 @@ void MergeFunctions::WriteThunk(Function *F, Function *G) const {
NewG->takeName(G);
G->replaceAllUsesWith(NewG);
G->eraseFromParent();
DEBUG(dbgs() << "WriteThunk: " << NewG->getName() << '\n');
++NumThunksWritten;
}
/// MergeTwoFunctions - Merge two equivalent functions. Upon completion,
/// Function G is deleted.
void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) const {
if (F->isWeakForLinker()) {
assert(G->isWeakForLinker());
if (F->mayBeOverridden()) {
assert(G->mayBeOverridden());
// Make them both thunks to the same internal function.
Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
@ -623,6 +631,8 @@ void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) const {
F->setAlignment(MaxAlignment);
F->setLinkage(GlobalValue::InternalLinkage);
++NumDoubleWeak;
} else {
WriteThunk(F, G);
}
@ -640,8 +650,8 @@ bool MergeFunctions::Insert(FnSetType &FnSet, ComparableFunction &NewF) {
const ComparableFunction &OldF = *Result.first;
// Never thunk a strong function to a weak function.
assert(!OldF.getFunc()->isWeakForLinker() ||
NewF.getFunc()->isWeakForLinker());
assert(!OldF.getFunc()->mayBeOverridden() ||
NewF.getFunc()->mayBeOverridden());
DEBUG(dbgs() << " " << OldF.getFunc()->getName() << " == "
<< NewF.getFunc()->getName() << '\n');
@ -660,8 +670,7 @@ static bool IsThunk(const Function *F) {
// then we may try to merge unmergable thing (ie., identical weak functions)
// which will push us into an infinite loop.
if (F->size() != 1)
return false;
assert(!F->isDeclaration() && "Expected a function definition.");
const BasicBlock *BB = &F->front();
// A thunk is:
@ -670,6 +679,10 @@ static bool IsThunk(const Function *F) {
// 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;
@ -677,18 +690,22 @@ static bool IsThunk(const Function *F) {
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;
if ((int)A->getArgNo() <= LastArgNo) return false;
LastArgNo = A->getArgNo();
++I;
}
// 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.
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);
@ -708,8 +725,7 @@ static bool IsThunk(const Function *F) {
if (BCI->getOperand(0) != CI) return false;
RetOp = BCI;
}
const ReturnInst *RI = dyn_cast<ReturnInst>(I);
if (!RI) return false;
if (RI != I) return false;
if (RI->getNumOperands() == 0)
return CI->getType()->isVoidTy();
return RI->getReturnValue() == CI;
@ -721,7 +737,7 @@ bool MergeFunctions::runOnModule(Module &M) {
bool LocalChanged;
do {
DEBUG(dbgs() << "size: " << M.size() << '\n');
DEBUG(dbgs() << "size of module: " << M.size() << '\n');
LocalChanged = false;
FnSetType FnSet;
@ -730,7 +746,7 @@ bool MergeFunctions::runOnModule(Module &M) {
for (Module::iterator I = M.begin(), E = M.end(); I != E;) {
Function *F = I++;
if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
!F->isWeakForLinker() && !IsThunk(F)) {
!F->mayBeOverridden() && !IsThunk(F)) {
ComparableFunction CF = ComparableFunction(F, TD);
LocalChanged |= Insert(FnSet, CF);
}
@ -743,11 +759,12 @@ bool MergeFunctions::runOnModule(Module &M) {
for (Module::iterator I = M.begin(), E = M.end(); I != E;) {
Function *F = I++;
if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
F->isWeakForLinker() && !IsThunk(F)) {
F->mayBeOverridden() && !IsThunk(F)) {
ComparableFunction CF = ComparableFunction(F, TD);
LocalChanged |= Insert(FnSet, CF);
}
}
DEBUG(dbgs() << "size of FnSet: " << FnSet.size() << '\n');
Changed |= LocalChanged;
} while (LocalChanged);