#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Constants.h"
+#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
+#include "llvm/Transforms/Utils/CtorUtils.h"
#include "llvm/Pass.h"
using namespace llvm;
};
}
+/// Returns true if F contains only a single "ret" instruction.
+static bool isEmptyFunction(Function *F) {
+ BasicBlock &Entry = F->getEntryBlock();
+ if (Entry.size() != 1 || !isa<ReturnInst>(Entry.front()))
+ return false;
+ ReturnInst &RI = cast<ReturnInst>(Entry.front());
+ return RI.getReturnValue() == nullptr;
+}
+
char GlobalDCE::ID = 0;
INITIALIZE_PASS(GlobalDCE, "globaldce",
"Dead Global Elimination", false, false)
bool GlobalDCE::runOnModule(Module &M) {
bool Changed = false;
-
+
+ // Remove empty functions from the global ctors list.
+ Changed |= optimizeGlobalCtorsList(M, isEmptyFunction);
+
+ typedef std::multimap<const Comdat *, GlobalValue *> ComdatGVPairsTy;
+ ComdatGVPairsTy ComdatGVPairs;
+
// Loop over the module, adding globals which are obviously necessary.
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
Changed |= RemoveUnusedGlobalValue(*I);
// Functions with external linkage are needed if they have a body
- if (!I->isDiscardableIfUnused() &&
- !I->isDeclaration() && !I->hasAvailableExternallyLinkage())
- GlobalIsNeeded(I);
+ if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) {
+ if (!I->isDiscardableIfUnused())
+ GlobalIsNeeded(I);
+ else if (const Comdat *C = I->getComdat())
+ ComdatGVPairs.insert(std::make_pair(C, I));
+ }
}
for (Module::global_iterator I = M.global_begin(), E = M.global_end();
Changed |= RemoveUnusedGlobalValue(*I);
// Externally visible & appending globals are needed, if they have an
// initializer.
- if (!I->isDiscardableIfUnused() &&
- !I->isDeclaration() && !I->hasAvailableExternallyLinkage())
- GlobalIsNeeded(I);
+ if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) {
+ if (!I->isDiscardableIfUnused())
+ GlobalIsNeeded(I);
+ else if (const Comdat *C = I->getComdat())
+ ComdatGVPairs.insert(std::make_pair(C, I));
+ }
}
for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
I != E; ++I) {
Changed |= RemoveUnusedGlobalValue(*I);
// Externally visible aliases are needed.
- if (!I->isDiscardableIfUnused())
+ if (!I->isDiscardableIfUnused()) {
GlobalIsNeeded(I);
+ } else if (const Comdat *C = I->getComdat()) {
+ ComdatGVPairs.insert(std::make_pair(C, I));
+ }
+ }
+
+ for (ComdatGVPairsTy::iterator I = ComdatGVPairs.begin(),
+ E = ComdatGVPairs.end();
+ I != E;) {
+ ComdatGVPairsTy::iterator UB = ComdatGVPairs.upper_bound(I->first);
+ bool CanDiscard = std::all_of(I, UB, [](ComdatGVPairsTy::value_type Pair) {
+ return Pair.second->isDiscardableIfUnused();
+ });
+ if (!CanDiscard) {
+ std::for_each(I, UB, [this](ComdatGVPairsTy::value_type Pair) {
+ GlobalIsNeeded(Pair.second);
+ });
+ }
+ I = UB;
}
// Now that all globals which are needed are in the AliveGlobals set, we loop