ElimAvailExtern.cpp [plain text]
#include "llvm/Transforms/IPO.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Module.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
#include "llvm/Pass.h"
using namespace llvm;
#define DEBUG_TYPE "elim-avail-extern"
STATISTIC(NumFunctions, "Number of functions removed");
STATISTIC(NumVariables, "Number of global variables removed");
namespace {
struct EliminateAvailableExternally : public ModulePass {
static char ID; EliminateAvailableExternally() : ModulePass(ID) {
initializeEliminateAvailableExternallyPass(
*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override;
};
}
char EliminateAvailableExternally::ID = 0;
INITIALIZE_PASS(EliminateAvailableExternally, "elim-avail-extern",
"Eliminate Available Externally Globals", false, false)
ModulePass *llvm::createEliminateAvailableExternallyPass() {
return new EliminateAvailableExternally();
}
static void convertAliasToDeclaration(GlobalAlias &GA, Module &M) {
GlobalValue *GVal = GA.getBaseObject();
GlobalValue *NewGV;
if (auto *GVar = dyn_cast<GlobalVariable>(GVal)) {
GlobalVariable *NewGVar = new GlobalVariable(
M, GVar->getType()->getElementType(), GVar->isConstant(),
GVar->getLinkage(), nullptr, GA.getName(), GVar,
GVar->getThreadLocalMode(), GVar->getType()->getAddressSpace());
NewGV = NewGVar;
NewGV->copyAttributesFrom(GVar);
} else {
auto *F = dyn_cast<Function>(GVal);
assert(F);
Function *NewF = Function::Create(F->getFunctionType(), F->getLinkage(),
GA.getName(), &M);
NewGV = NewF;
NewGV->copyAttributesFrom(F);
}
GA.replaceAllUsesWith(ConstantExpr::getBitCast(NewGV, GA.getType()));
GA.eraseFromParent();
}
bool EliminateAvailableExternally::runOnModule(Module &M) {
bool Changed = false;
for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E;) {
GlobalAlias &GA = *(I++);
GlobalValue *GVal = GA.getBaseObject();
if (!GVal->hasAvailableExternallyLinkage())
continue;
convertAliasToDeclaration(GA, M);
Changed = true;
}
for (GlobalVariable &GV : M.globals()) {
if (!GV.hasAvailableExternallyLinkage())
continue;
if (GV.hasInitializer()) {
Constant *Init = GV.getInitializer();
GV.setInitializer(nullptr);
if (isSafeToDestroyConstant(Init))
Init->destroyConstant();
}
GV.removeDeadConstantUsers();
GV.setLinkage(GlobalValue::ExternalLinkage);
NumVariables++;
Changed = true;
}
for (Function &F : M) {
if (!F.hasAvailableExternallyLinkage())
continue;
if (!F.isDeclaration())
F.deleteBody();
F.removeDeadConstantUsers();
NumFunctions++;
Changed = true;
}
return Changed;
}