//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/Compiler.h"
#include <set>
using namespace llvm;
+STATISTIC(NumAliases , "Number of global aliases removed");
STATISTIC(NumFunctions, "Number of functions removed");
STATISTIC(NumVariables, "Number of global variables removed");
namespace {
- struct GlobalDCE : public ModulePass {
+ struct VISIBILITY_HIDDEN GlobalDCE : public ModulePass {
+ static char ID; // Pass identification, replacement for typeid
+ GlobalDCE() : ModulePass(&ID) {}
+
// run - Do the GlobalDCE pass on the specified module, optionally updating
// the specified callgraph to reflect the changes.
//
private:
std::set<GlobalValue*> AliveGlobals;
- /// MarkGlobalIsNeeded - the specific global value as needed, and
+ /// 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);
- bool SafeToDestroyConstant(Constant* C);
bool RemoveUnusedGlobalValue(GlobalValue &GV);
};
- RegisterPass<GlobalDCE> X("globaldce", "Dead Global Elimination");
}
+char GlobalDCE::ID = 0;
+static RegisterPass<GlobalDCE> X("globaldce", "Dead Global Elimination");
+
ModulePass *llvm::createGlobalDCEPass() { return new GlobalDCE(); }
bool GlobalDCE::runOnModule(Module &M) {
bool Changed = false;
+
// 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->hasInternalLinkage() && !I->hasLinkOnceLinkage()) &&
- !I->isExternal())
+ if (!I->hasLocalLinkage() && !I->hasLinkOnceLinkage() &&
+ !I->isDeclaration() && !I->hasAvailableExternallyLinkage())
GlobalIsNeeded(I);
}
- 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) {
Changed |= RemoveUnusedGlobalValue(*I);
// Externally visible & appending globals are needed, if they have an
// initializer.
- if ((!I->hasInternalLinkage() && !I->hasLinkOnceLinkage()) &&
- !I->isExternal())
+ if (!I->hasLocalLinkage() && !I->hasLinkOnceLinkage() &&
+ !I->isDeclaration() && !I->hasAvailableExternallyLinkage())
GlobalIsNeeded(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())
+ GlobalIsNeeded(I);
+ }
// Now that all globals which are needed are in the AliveGlobals set, we loop
// through the program, deleting those which are not alive.
I->setInitializer(0);
}
-
// The second pass drops the bodies of functions which are dead...
std::vector<Function*> DeadFunctions;
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
if (!AliveGlobals.count(I)) {
DeadFunctions.push_back(I); // Keep track of dead globals
- if (!I->isExternal())
+ if (!I->isDeclaration())
I->deleteBody();
}
+ // The third pass drops targets of aliases which are dead...
+ std::vector<GlobalAlias*> DeadAliases;
+ for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E;
+ ++I)
+ if (!AliveGlobals.count(I)) {
+ DeadAliases.push_back(I);
+ I->setAliasee(0);
+ }
+
if (!DeadFunctions.empty()) {
- // Now that all interreferences have been dropped, delete the actual objects
+ // Now that all interferences have been dropped, delete the actual objects
// themselves.
for (unsigned i = 0, e = DeadFunctions.size(); i != e; ++i) {
RemoveUnusedGlobalValue(*DeadFunctions[i]);
Changed = true;
}
+ // Now delete any dead aliases.
+ if (!DeadAliases.empty()) {
+ for (unsigned i = 0, e = DeadAliases.size(); i != e; ++i) {
+ RemoveUnusedGlobalValue(*DeadAliases[i]);
+ M.getAliasList().erase(DeadAliases[i]);
+ }
+ NumAliases += DeadAliases.size();
+ Changed = true;
+ }
+
// Make sure that all memory is released
AliveGlobals.clear();
+
+ // Remove dead metadata.
+ Changed |= M.getContext().RemoveDeadMetadata();
return Changed;
}
-/// MarkGlobalIsNeeded - the specific global value as needed, and
+/// 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.lower_bound(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() && *I == G) return;
+ if (I != AliveGlobals.end()) return;
// Otherwise insert it now, so we do not infinitely recurse
AliveGlobals.insert(I, G);
// referenced by the initializer to the alive set.
if (GV->hasInitializer())
MarkUsedGlobalsAsNeeded(GV->getInitializer());
+ } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(G)) {
+ // The target of a global alias is needed.
+ MarkUsedGlobalsAsNeeded(GA->getAliasee());
} else {
// Otherwise this must be a function object. We have to scan the body of
// the function looking for constants and global values which are used as
GV.removeDeadConstantUsers();
return GV.use_empty();
}
-
-// SafeToDestroyConstant - It is safe to destroy a constant iff it is only used
-// by constants itself. Note that constants cannot be cyclic, so this test is
-// pretty easy to implement recursively.
-//
-bool GlobalDCE::SafeToDestroyConstant(Constant *C) {
- for (Value::use_iterator I = C->use_begin(), E = C->use_end(); I != E; ++I)
- if (Constant *User = dyn_cast<Constant>(*I)) {
- if (!SafeToDestroyConstant(User)) return false;
- } else {
- return false;
- }
- return true;
-}
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