#include "llvm/Transforms/IPO.h"
#include "llvm/Module.h"
-#include "llvm/Function.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Analysis/CallGraph.h"
#include "Support/DepthFirstIterator.h"
#include "Support/StatisticReporter.h"
+#include <algorithm>
static Statistic<> NumFunctions("globaldce\t- Number of functions removed");
static Statistic<> NumVariables("globaldce\t- Number of global variables removed");
+static Statistic<> NumCPRs("globaldce\t- Number of const pointer refs removed");
+static Statistic<> NumConsts("globaldce\t- Number of init constants removed");
static bool RemoveUnreachableFunctions(Module &M, CallGraph &CallGraph) {
// Calculate which functions are reachable from the external functions in the
return true;
}
-static bool RemoveUnreachableGlobalVariables(Module &M) {
- bool Changed = false;
- // Eliminate all global variables that are unused, and that are internal, or
- // do not have an initializer.
- //
- for (Module::giterator I = M.gbegin(); I != M.gend(); )
- if (!I->use_empty() || (I->hasExternalLinkage() && I->hasInitializer()))
- ++I; // Cannot eliminate global variable
- else {
- I = M.getGlobalList().erase(I);
- ++NumVariables;
- Changed = true;
- }
- return Changed;
-}
-
namespace {
struct GlobalDCE : public Pass {
// run - Do the GlobalDCE pass on the specified module, optionally updating
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<CallGraph>();
}
+
+ private:
+ std::vector<GlobalValue*> WorkList;
+
+ inline bool RemoveIfDead(GlobalValue *GV);
+ void DestroyInitializer(Constant *C);
+
+ bool RemoveUnreachableGlobalVariables(Module &M);
+ bool RemoveUnusedConstantPointerRef(GlobalValue &GV);
+ bool SafeToDestroyConstant(Constant *C);
};
RegisterOpt<GlobalDCE> X("globaldce", "Dead Global Elimination");
}
Pass *createGlobalDCEPass() { return new GlobalDCE(); }
+
+
+// RemoveIfDead - If this global value is dead, remove it from the current
+// module and return true.
+//
+bool GlobalDCE::RemoveIfDead(GlobalValue *GV) {
+ // If there is only one use of the global value, it might be a
+ // ConstantPointerRef... which means that this global might actually be
+ // dead.
+ if (GV->use_size() == 1)
+ RemoveUnusedConstantPointerRef(*GV);
+
+ if (!GV->use_empty()) return false;
+
+ if (GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV)) {
+ // Eliminate all global variables that are unused, and that are internal, or
+ // do not have an initializer.
+ //
+ if (!GVar->hasExternalLinkage() || !GVar->hasInitializer()) {
+ Constant *Init = GVar->hasInitializer() ? GVar->getInitializer() : 0;
+ GV->getParent()->getGlobalList().erase(GVar);
+ ++NumVariables;
+
+ // If there was an initializer for the global variable, try to destroy it
+ // now.
+ if (Init) DestroyInitializer(Init);
+
+ // If the global variable is still on the worklist, remove it now.
+ std::vector<GlobalValue*>::iterator I = std::find(WorkList.begin(),
+ WorkList.end(), GV);
+ while (I != WorkList.end())
+ I = std::find(WorkList.erase(I), WorkList.end(), GV);
+
+ return true;
+ }
+ } else {
+ Function *F = cast<Function>(GV);
+ // FIXME: TODO
+
+ }
+ return false;
+}
+
+// DestroyInitializer - A global variable was just destroyed and C is its
+// initializer. If we can, destroy C and all of the constants it refers to.
+//
+void GlobalDCE::DestroyInitializer(Constant *C) {
+ // Cannot destroy constants still being used, and cannot destroy primitive
+ // types.
+ if (!C->use_empty() || C->getType()->isPrimitiveType()) return;
+
+ // If this is a CPR, the global value referred to may be dead now! Add it to
+ // the worklist.
+ //
+ if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(C)) {
+ WorkList.push_back(CPR->getValue());
+ C->destroyConstant();
+ ++NumCPRs;
+ } else {
+ bool DestroyContents = true;
+
+ // As an optimization to the GlobalDCE algorithm, do attempt to destroy the
+ // contents of an array of primitive types, because we know that this will
+ // never succeed, and there could be a lot of them.
+ //
+ if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
+ if (CA->getType()->getElementType()->isPrimitiveType())
+ DestroyContents = false; // Nothing we can do with the subcontents
+
+ // All other constants refer to other constants. Destroy them if possible
+ // as well.
+ //
+ std::vector<Value*> SubConstants;
+ if (DestroyContents) SubConstants.insert(SubConstants.end(),
+ C->op_begin(), C->op_end());
+
+ // Destroy the actual constant...
+ C->destroyConstant();
+ ++NumConsts;
+
+ if (DestroyContents) {
+ // Remove duplicates from SubConstants, so that we do not call
+ // DestroyInitializer on the same constant twice (the first call might
+ // delete it, so this would be bad)
+ //
+ std::sort(SubConstants.begin(), SubConstants.end());
+ SubConstants.erase(std::unique(SubConstants.begin(), SubConstants.end()),
+ SubConstants.end());
+
+ // Loop over the subconstants, destroying them as well.
+ for (unsigned i = 0, e = SubConstants.size(); i != e; ++i)
+ DestroyInitializer(cast<Constant>(SubConstants[i]));
+ }
+ }
+}
+
+bool GlobalDCE::RemoveUnreachableGlobalVariables(Module &M) {
+ bool Changed = false;
+ WorkList.reserve(M.gsize());
+
+ // Insert all of the globals into the WorkList, making sure to run
+ // RemoveUnusedConstantPointerRef at least once on all globals...
+ //
+ for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
+ Changed |= RemoveUnusedConstantPointerRef(*I);
+ WorkList.push_back(I);
+ }
+ for (Module::giterator I = M.gbegin(), E = M.gend(); I != E; ++I) {
+ Changed |= RemoveUnusedConstantPointerRef(*I);
+ WorkList.push_back(I);
+ }
+
+ // Loop over the worklist, deleting global objects that we can. Whenever we
+ // delete something that might make something else dead, it gets added to the
+ // worklist.
+ //
+ while (!WorkList.empty()) {
+ GlobalValue *GV = WorkList.back();
+ WorkList.pop_back();
+
+ Changed |= RemoveIfDead(GV);
+ }
+
+ // Make sure that all memory is free'd from the worklist...
+ std::vector<GlobalValue*>().swap(WorkList);
+ return Changed;
+}
+
+
+// RemoveUnusedConstantPointerRef - Loop over all of the uses of the specified
+// GlobalValue, looking for the constant pointer ref that may be pointing to it.
+// If found, check to see if the constant pointer ref is safe to destroy, and if
+// so, nuke it. This will reduce the reference count on the global value, which
+// might make it deader.
+//
+bool GlobalDCE::RemoveUnusedConstantPointerRef(GlobalValue &GV) {
+ for (Value::use_iterator I = GV.use_begin(), E = GV.use_end(); I != E; ++I)
+ if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(*I))
+ if (SafeToDestroyConstant(CPR)) { // Only if unreferenced...
+ CPR->destroyConstant();
+ ++NumCPRs;
+ return true;
+ }
+
+ return false;
+}
+
+// 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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