//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "globaldce"
#include "llvm/Transforms/IPO.h"
-#include "llvm/Constants.h"
-#include "llvm/Module.h"
-#include "llvm/Pass.h"
+#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/Support/Compiler.h"
-#include <set>
+#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;
+#define DEBUG_TYPE "globaldce"
+
STATISTIC(NumAliases , "Number of global aliases removed");
STATISTIC(NumFunctions, "Number of functions removed");
STATISTIC(NumVariables, "Number of global variables removed");
namespace {
- struct VISIBILITY_HIDDEN GlobalDCE : public ModulePass {
+ struct GlobalDCE : public ModulePass {
static char ID; // Pass identification, replacement for typeid
- GlobalDCE() : ModulePass(&ID) {}
+ GlobalDCE() : ModulePass(ID) {
+ initializeGlobalDCEPass(*PassRegistry::getPassRegistry());
+ }
// run - Do the GlobalDCE pass on the specified module, optionally updating
// the specified callgraph to reflect the changes.
//
- bool runOnModule(Module &M);
+ bool runOnModule(Module &M) override;
private:
- std::set<GlobalValue*> AliveGlobals;
+ SmallPtrSet<Constant *, 32> AliveGlobals;
+ SmallPtrSet<Constant *, 8> SeenConstants;
+ SmallPtrSet<GlobalVariable *, 8> DiscardableGlobalInitializers;
/// GlobalIsNeeded - mark the specific global value as needed, and
/// recursively mark anything that it uses as also needed.
void GlobalIsNeeded(GlobalValue *GV);
void MarkUsedGlobalsAsNeeded(Constant *C);
+ /// \brief Checks if C is alive or is a ConstantExpr that refers to an alive
+ /// value.
+ bool ContainsUsedGlobal(Constant *C);
+
bool RemoveUnusedGlobalValue(GlobalValue &GV);
};
}
+/// 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;
-static RegisterPass<GlobalDCE> X("globaldce", "Dead Global Elimination");
+INITIALIZE_PASS(GlobalDCE, "globaldce",
+ "Dead Global Elimination", false, false)
ModulePass *llvm::createGlobalDCEPass() { return new GlobalDCE(); }
bool GlobalDCE::runOnModule(Module &M) {
bool Changed = false;
- Context = &M.getContext();
-
+
+ // 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->hasLocalLinkage() && !I->hasLinkOnceLinkage() &&
- !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->hasLocalLinkage() && !I->hasLinkOnceLinkage() &&
- !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->hasLocalLinkage() && !I->hasLinkOnceLinkage())
+ 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
// The first pass is to drop initializers of global variables which are dead.
std::vector<GlobalVariable*> DeadGlobalVars; // Keep track of dead globals
- for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I)
+ for (Module::global_iterator I = M.global_begin(), E = M.global_end();
+ I != E; ++I)
if (!AliveGlobals.count(I)) {
DeadGlobalVars.push_back(I); // Keep track of dead globals
- I->setInitializer(0);
+ I->setInitializer(nullptr);
}
// The second pass drops the bodies of functions which are dead...
++I)
if (!AliveGlobals.count(I)) {
DeadAliases.push_back(I);
- I->setAliasee(0);
+ I->setAliasee(nullptr);
+ }
+
+ // Look for available externally constants that we can turn into normal
+ // externals by deleting their initalizers. This allows us to remove other
+ // globals that are referenced by the initializer.
+ if (!DiscardableGlobalInitializers.empty()) {
+ for (GlobalVariable *GV : DiscardableGlobalInitializers) {
+ if (!ContainsUsedGlobal(GV->getInitializer())) {
+ GV->setInitializer(nullptr);
+ GV->setLinkage(GlobalValue::ExternalLinkage);
+ Changed = true;
+ }
}
+ }
if (!DeadFunctions.empty()) {
// Now that all interferences have been dropped, delete the actual objects
// Make sure that all memory is released
AliveGlobals.clear();
+ SeenConstants.clear();
+
return Changed;
}
/// GlobalIsNeeded - the specific global value as needed, and
/// recursively mark anything that it uses as also needed.
void GlobalDCE::GlobalIsNeeded(GlobalValue *G) {
- std::set<GlobalValue*>::iterator I = AliveGlobals.find(G);
-
// If the global is already in the set, no need to reprocess it.
- if (I != AliveGlobals.end()) return;
-
- // Otherwise insert it now, so we do not infinitely recurse
- AliveGlobals.insert(I, G);
-
+ if (!AliveGlobals.insert(G))
+ return;
+
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(G)) {
// If this is a global variable, we must make sure to add any global values
// referenced by the initializer to the alive set.
- if (GV->hasInitializer())
- MarkUsedGlobalsAsNeeded(GV->getInitializer());
+ if (GV->hasInitializer()) {
+ if (GV->hasAvailableExternallyLinkage())
+ DiscardableGlobalInitializers.insert(GV);
+ else
+ MarkUsedGlobalsAsNeeded(GV->getInitializer());
+ }
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(G)) {
// The target of a global alias is needed.
MarkUsedGlobalsAsNeeded(GA->getAliasee());
// operands. Any operands of these types must be processed to ensure that
// any globals used will be marked as needed.
Function *F = cast<Function>(G);
- // For all basic blocks...
+
+ if (F->hasPrefixData())
+ MarkUsedGlobalsAsNeeded(F->getPrefixData());
+
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
- // For all instructions...
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
- // For all operands...
for (User::op_iterator U = I->op_begin(), E = I->op_end(); U != E; ++U)
if (GlobalValue *GV = dyn_cast<GlobalValue>(*U))
GlobalIsNeeded(GV);
void GlobalDCE::MarkUsedGlobalsAsNeeded(Constant *C) {
if (GlobalValue *GV = dyn_cast<GlobalValue>(C))
- GlobalIsNeeded(GV);
- else {
- // Loop over all of the operands of the constant, adding any globals they
- // use to the list of needed globals.
- for (User::op_iterator I = C->op_begin(), E = C->op_end(); I != E; ++I)
- MarkUsedGlobalsAsNeeded(cast<Constant>(*I));
+ return GlobalIsNeeded(GV);
+
+ // Loop over all of the operands of the constant, adding any globals they
+ // use to the list of needed globals.
+ for (User::op_iterator I = C->op_begin(), E = C->op_end(); I != E; ++I) {
+ // If we've already processed this constant there's no need to do it again.
+ Constant *Op = dyn_cast<Constant>(*I);
+ if (Op && SeenConstants.insert(Op))
+ MarkUsedGlobalsAsNeeded(Op);
+ }
+}
+
+bool GlobalDCE::ContainsUsedGlobal(Constant *C) {
+ // C contains a used global If C is alive or we visited it while marking
+ // values alive.
+ if (AliveGlobals.count(C) || SeenConstants.count(C))
+ return true;
+
+ // Now check all operands of a ConstantExpr.
+ for (User::op_iterator I = C->op_begin(), E = C->op_end(); I != E; ++I) {
+ Constant *Op = dyn_cast<Constant>(*I);
+ if (Op && ContainsUsedGlobal(Op))
+ return true;
}
+ return false;
}
// RemoveUnusedGlobalValue - Loop over all of the uses of the specified
projects / oota-llvm.git / blobdiff