using namespace llvm;
STATISTIC(NumMarked , "Number of globals marked constant");
+STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr");
STATISTIC(NumSRA , "Number of aggregate globals broken into scalars");
STATISTIC(NumHeapSRA , "Number of heap objects SRA'd");
STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
STATISTIC(NumNestRemoved , "Number of nest attributes removed");
STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
+STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
namespace {
+ struct GlobalStatus;
struct GlobalOpt : public ModulePass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
}
bool OptimizeGlobalVars(Module &M);
bool OptimizeGlobalAliases(Module &M);
bool OptimizeGlobalCtorsList(GlobalVariable *&GCL);
- bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI);
+ bool ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI);
+ bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI,
+ const SmallPtrSet<const PHINode*, 16> &PHIUsers,
+ const GlobalStatus &GS);
+ bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn);
};
}
/// about it. If we find out that the address of the global is taken, none of
/// this info will be accurate.
struct GlobalStatus {
+ /// isCompared - True if the global's address is used in a comparison.
+ bool isCompared;
+
/// isLoaded - True if the global is ever loaded. If the global isn't ever
/// loaded it can be deleted.
bool isLoaded;
/// HasPHIUser - Set to true if this global has a user that is a PHI node.
bool HasPHIUser;
- GlobalStatus() : isLoaded(false), StoredType(NotStored), StoredOnceValue(0),
- AccessingFunction(0), HasMultipleAccessingFunctions(false),
- HasNonInstructionUser(false), HasPHIUser(false) {}
+ GlobalStatus() : isCompared(false), isLoaded(false), StoredType(NotStored),
+ StoredOnceValue(0), AccessingFunction(0),
+ HasMultipleAccessingFunctions(false), HasNonInstructionUser(false),
+ HasPHIUser(false) {}
};
}
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
GS.HasPHIUser = true;
} else if (isa<CmpInst>(I)) {
- // Nothing to analyse.
+ GS.isCompared = true;
} else if (isa<MemTransferInst>(I)) {
const MemTransferInst *MTI = cast<MemTransferInst>(I);
if (MTI->getArgOperand(0) == V)
const StructType *ST =
cast<StructType>(cast<PointerType>(PN->getType())->getElementType());
- Result =
+ PHINode *NewPN =
PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)),
+ PN->getNumIncomingValues(),
PN->getName()+".f"+Twine(FieldNo), PN);
+ Result = NewPN;
PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
} else {
llvm_unreachable("Unknown usable value");
/// ProcessInternalGlobal - Analyze the specified global variable and optimize
/// it if possible. If we make a change, return true.
-bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
- Module::global_iterator &GVI) {
- SmallPtrSet<const PHINode*, 16> PHIUsers;
- GlobalStatus GS;
+bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
+ Module::global_iterator &GVI) {
+ if (!GV->hasLocalLinkage())
+ return false;
+
+ // Do more involved optimizations if the global is internal.
GV->removeDeadConstantUsers();
if (GV->use_empty()) {
return true;
}
+ SmallPtrSet<const PHINode*, 16> PHIUsers;
+ GlobalStatus GS;
+
if (AnalyzeGlobal(GV, GS, PHIUsers))
return false;
+ if (!GS.isCompared && !GV->hasUnnamedAddr()) {
+ GV->setUnnamedAddr(true);
+ NumUnnamed++;
+ }
+
+ if (GV->isConstant() || !GV->hasInitializer())
+ return false;
+
+ return ProcessInternalGlobal(GV, GVI, PHIUsers, GS);
+}
+
+/// ProcessInternalGlobal - Analyze the specified global variable and optimize
+/// it if possible. If we make a change, return true.
+bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
+ Module::global_iterator &GVI,
+ const SmallPtrSet<const PHINode*, 16> &PHIUsers,
+ const GlobalStatus &GS) {
// If this is a first class global and has only one accessing function
// and this function is main (which we know is not recursive we can make
// this global a local variable) we replace the global with a local alloca
if (New && New != CE)
GV->setInitializer(New);
}
- // Do more involved optimizations if the global is internal.
- if (!GV->isConstant() && GV->hasLocalLinkage() &&
- GV->hasInitializer())
- Changed |= ProcessInternalGlobal(GV, GVI);
+
+ Changed |= ProcessGlobal(GV, GVI);
}
return Changed;
}
if (Init->getType()->isArrayTy())
return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
- else
- return ConstantVector::get(&Elts[0], Elts.size());
+ return ConstantVector::get(Elts);
}
}
return Changed;
}
+static Function *FindCXAAtExit(Module &M) {
+ Function *Fn = M.getFunction("__cxa_atexit");
+
+ if (!Fn)
+ return 0;
+
+ const FunctionType *FTy = Fn->getFunctionType();
+
+ // Checking that the function has the right return type, the right number of
+ // parameters and that they all have pointer types should be enough.
+ if (!FTy->getReturnType()->isIntegerTy() ||
+ FTy->getNumParams() != 3 ||
+ !FTy->getParamType(0)->isPointerTy() ||
+ !FTy->getParamType(1)->isPointerTy() ||
+ !FTy->getParamType(2)->isPointerTy())
+ return 0;
+
+ return Fn;
+}
+
+/// cxxDtorIsEmpty - Returns whether the given function is an empty C++
+/// destructor and can therefore be eliminated.
+/// Note that we assume that other optimization passes have already simplified
+/// the code so we only look for a function with a single basic block, where
+/// the only allowed instructions are 'ret' or 'call' to empty C++ dtor.
+static bool cxxDtorIsEmpty(const Function &Fn,
+ SmallPtrSet<const Function *, 8> &CalledFunctions) {
+ // FIXME: We could eliminate C++ destructors if they're readonly/readnone and
+ // nounwind, but that doesn't seem worth doing.
+ if (Fn.isDeclaration())
+ return false;
+
+ if (++Fn.begin() != Fn.end())
+ return false;
+
+ const BasicBlock &EntryBlock = Fn.getEntryBlock();
+ for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
+ I != E; ++I) {
+ if (const CallInst *CI = dyn_cast<CallInst>(I)) {
+ // Ignore debug intrinsics.
+ if (isa<DbgInfoIntrinsic>(CI))
+ continue;
+
+ const Function *CalledFn = CI->getCalledFunction();
+
+ if (!CalledFn)
+ return false;
+
+ SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
+
+ // Don't treat recursive functions as empty.
+ if (!NewCalledFunctions.insert(CalledFn))
+ return false;
+
+ if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
+ return false;
+ } else if (isa<ReturnInst>(*I))
+ return true;
+ else
+ return false;
+ }
+
+ return false;
+}
+
+bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
+ /// Itanium C++ ABI p3.3.5:
+ ///
+ /// After constructing a global (or local static) object, that will require
+ /// destruction on exit, a termination function is registered as follows:
+ ///
+ /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
+ ///
+ /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
+ /// call f(p) when DSO d is unloaded, before all such termination calls
+ /// registered before this one. It returns zero if registration is
+ /// successful, nonzero on failure.
+
+ // This pass will look for calls to __cxa_atexit where the function is trivial
+ // and remove them.
+ bool Changed = false;
+
+ for (Function::use_iterator I = CXAAtExitFn->use_begin(),
+ E = CXAAtExitFn->use_end(); I != E;) {
+ // We're only interested in calls. Theoretically, we could handle invoke
+ // instructions as well, but neither llvm-gcc nor clang generate invokes
+ // to __cxa_atexit.
+ CallInst *CI = dyn_cast<CallInst>(*I++);
+ if (!CI)
+ continue;
+
+ Function *DtorFn =
+ dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
+ if (!DtorFn)
+ continue;
+
+ SmallPtrSet<const Function *, 8> CalledFunctions;
+ if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
+ continue;
+
+ // Just remove the call.
+ CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
+ CI->eraseFromParent();
+
+ ++NumCXXDtorsRemoved;
+
+ Changed |= true;
+ }
+
+ return Changed;
+}
+
bool GlobalOpt::runOnModule(Module &M) {
bool Changed = false;
// Try to find the llvm.globalctors list.
GlobalVariable *GlobalCtors = FindGlobalCtors(M);
+ Function *CXAAtExitFn = FindCXAAtExit(M);
+
bool LocalChange = true;
while (LocalChange) {
LocalChange = false;
// Resolve aliases, when possible.
LocalChange |= OptimizeGlobalAliases(M);
+
+ // Try to remove trivial global destructors.
+ if (CXAAtExitFn)
+ LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
+
Changed |= LocalChange;
}
projects / oota-llvm.git / blobdiff