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* Rename pass to globalopt, since we do more than just constify

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* Instead of handling dead functions specially, just nuke them.
* Be more aggressive about cleaning up after constification, in
  particular, handle getelementptr instructions and constantexprs.
* Be a little bit more structured about how we process globals.

*** Delete globals that are only stored to, and never read.  These are
    clearly not useful, so they should go.  This implements deadglobal.llx

This last one triggers quite a few times.  In particular, 2208 in the
external tests, 1865 of which are in 252.eon.  This shrinks eon from
1995094 to 1732341 bytes of bytecode.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16802 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-10-07 04:16:33 +00:00
parent 93a00e4ceb
commit 7a90b68e5c
1 changed files with 182 additions and 79 deletions
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261
lib/Transforms/IPO/GlobalOpt.cpp
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@ -1,4 +1,4 @@
//===- GlobalConstifier.cpp - Mark read-only globals constant -------------===//
//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
//
// The LLVM Compiler Infrastructure
//
@ -7,19 +7,16 @@
//
//===----------------------------------------------------------------------===//
//
// This pass loops over the non-constant internal global variables in the
// program. If it can prove that they are never written to, it marks them
// constant.
//
// NOTE: this should eventually use the alias analysis interfaces to do the
// transformation, but for now we just stick with a simple solution. DSA in
// particular could give a much more accurate answer to the mod/ref query, but
// it's not quite ready for this.
// This pass transforms simple global variables that never have their address
// taken. If obviously true, it marks read/write globals as constant, deletes
// variables only stored to, etc.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "globalopt"
#include "llvm/Transforms/IPO.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
@ -30,60 +27,84 @@
using namespace llvm;
namespace {
Statistic<> NumMarked ("constify", "Number of globals marked constant");
Statistic<> NumDeleted("constify", "Number of globals deleted");
Statistic<> NumMarked ("globalopt", "Number of globals marked constant");
Statistic<> NumDeleted("globalopt", "Number of globals deleted");
Statistic<> NumFnDeleted("globalopt", "Number of functions deleted");
struct Constifier : public ModulePass {
struct GlobalOpt : public ModulePass {
bool runOnModule(Module &M);
};
RegisterOpt<Constifier> X("constify", "Global Constifier");
RegisterOpt<GlobalOpt> X("globalopt", "Global Variable Optimizer");
}
ModulePass *llvm::createGlobalConstifierPass() { return new Constifier(); }
ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
/// A lot of global constants are stored only in trivially dead setter
/// functions. Because we don't want to cycle between globaldce and this pass,
/// just do a simple check to catch the common case.
static bool ContainingFunctionIsTriviallyDead(Instruction *I) {
Function *F = I->getParent()->getParent();
if (!F->hasInternalLinkage()) return false;
F->removeDeadConstantUsers();
return F->use_empty();
}
/// GlobalStatus - As we analyze each global, keep track of some information
/// about it. If we find out that the address of the global is taken, none of
/// the other info will be accurate.
struct GlobalStatus {
bool isLoaded;
enum StoredType {
NotStored, isInitializerStored, isMallocStored, isStored
} StoredType;
bool isNotSuitableForSRA;
GlobalStatus() : isLoaded(false), StoredType(NotStored),
isNotSuitableForSRA(false) {}
};
/// isStoredThrough - Return false if the specified pointer is provably never
/// stored through. If we can't tell, we must conservatively assume it might.
/// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus
/// structure. If the global has its address taken, return true to indicate we
/// can't do anything with it.
///
static bool isStoredThrough(Value *V, std::set<PHINode*> &PHIUsers) {
static bool AnalyzeGlobal(Value *V, GlobalStatus &GS,
std::set<PHINode*> &PHIUsers) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
if (isStoredThrough(CE, PHIUsers))
return true;
if (AnalyzeGlobal(CE, GS, PHIUsers)) return true;
if (CE->getOpcode() != Instruction::GetElementPtr)
GS.isNotSuitableForSRA = true;
} else if (Instruction *I = dyn_cast<Instruction>(*UI)) {
if (!ContainingFunctionIsTriviallyDead(I)) {
if (I->getOpcode() == Instruction::GetElementPtr ||
I->getOpcode() == Instruction::Select) {
if (isStoredThrough(I, PHIUsers)) return true;
} else if (PHINode *PN = dyn_cast<PHINode>(I)) {
// PHI nodes we can check just like select or GEP instructions, but we
// have to be careful about infinite recursion.
if (PHIUsers.insert(PN).second) // Not already visited.
if (isStoredThrough(I, PHIUsers)) return true;
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
// If this store is just storing the initializer into a global
// (i.e. not changing the value), ignore it. For now we just handle
// direct stores, no stores to fields of aggregates.
if (!isa<GlobalVariable>(SI->getOperand(1)))
return true;
Constant *GVInit =
cast<GlobalVariable>(SI->getOperand(1))->getInitializer();
if (SI->getOperand(0) != GVInit)
return true;
} else if (!isa<LoadInst>(I) && !isa<SetCondInst>(I)) {
return true; // Any other non-load instruction might store!
if (isa<LoadInst>(I)) {
GS.isLoaded = true;
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
// If this store is just storing the initializer into a global (i.e. not
// changing the value), ignore it. For now we just handle direct
// stores, no stores to fields of aggregates.
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(SI->getOperand(1))) {
if (SI->getOperand(0) == GV->getInitializer() &&
GS.StoredType < GlobalStatus::isInitializerStored)
GS.StoredType = GlobalStatus::isInitializerStored;
else if (isa<MallocInst>(SI->getOperand(0)) &&
GS.StoredType < GlobalStatus::isMallocStored)
GS.StoredType = GlobalStatus::isMallocStored;
else
GS.StoredType = GlobalStatus::isStored;
} else {
GS.StoredType = GlobalStatus::isStored;
}
} else if (I->getOpcode() == Instruction::GetElementPtr) {
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
if (!GS.isNotSuitableForSRA)
for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i)
if (!isa<Constant>(I->getOperand(i))) {
GS.isNotSuitableForSRA = true;
break;
}
} else if (I->getOpcode() == Instruction::Select) {
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
GS.isNotSuitableForSRA = true;
} else if (PHINode *PN = dyn_cast<PHINode>(I)) {
// PHI nodes we can check just like select or GEP instructions, but we
// have to be careful about infinite recursion.
if (PHIUsers.insert(PN).second) // Not already visited.
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
GS.isNotSuitableForSRA = true;
} else if (isa<SetCondInst>(I)) {
GS.isNotSuitableForSRA = true;
} else {
return true; // Any other non-load instruction might take address!
}
} else {
// Otherwise must be a global or some other user.
@ -93,54 +114,136 @@ static bool isStoredThrough(Value *V, std::set<PHINode*> &PHIUsers) {
return false;
}
static Constant *TraverseGEPInitializer(User *GEP, Constant *Init) {
if (GEP->getNumOperands() == 1 ||
!isa<Constant>(GEP->getOperand(1)) ||
!cast<Constant>(GEP->getOperand(1))->isNullValue())
return 0;
for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) {
ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(i));
if (!Idx) return 0;
uint64_t IdxV = Idx->getRawValue();
if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) {
if (IdxV >= CS->getNumOperands()) return 0;
Init = CS->getOperand(IdxV);
} else if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) {
if (IdxV >= CA->getNumOperands()) return 0;
Init = CA->getOperand(IdxV);
} else if (ConstantPacked *CP = dyn_cast<ConstantPacked>(Init)) {
if (IdxV >= CP->getNumOperands()) return 0;
Init = CP->getOperand(IdxV);
} else if (ConstantAggregateZero *CAZ =
dyn_cast<ConstantAggregateZero>(Init)) {
if (const StructType *STy = dyn_cast<StructType>(Init->getType())) {
if (IdxV >= STy->getNumElements()) return 0;
Init = Constant::getNullValue(STy->getElementType(IdxV));
} else if (const SequentialType *STy =
dyn_cast<SequentialType>(Init->getType())) {
Init = Constant::getNullValue(STy->getElementType());
} else {
return 0;
}
} else {
return 0;
}
}
return Init;
}
/// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all
/// users of the global, cleaning up the obvious ones. This is largely just a
/// quick scan over the use list to clean up the easy and obvious cruft.
static void CleanupConstantGlobalUsers(GlobalVariable *GV) {
Constant *Init = GV->getInitializer();
if (!Init->getType()->isFirstClassType())
return; // We can't simplify aggregates yet!
std::vector<User*> Users(GV->use_begin(), GV->use_end());
std::sort(Users.begin(), Users.end());
Users.erase(std::unique(Users.begin(), Users.end()), Users.end());
for (unsigned i = 0, e = Users.size(); i != e; ++i) {
if (LoadInst *LI = dyn_cast<LoadInst>(Users[i])) {
static void CleanupConstantGlobalUsers(Value *V, Constant *Init) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) {
User *U = *UI++;
if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
// Replace the load with the initializer.
LI->replaceAllUsesWith(Init);
LI->getParent()->getInstList().erase(LI);
} else if (StoreInst *SI = dyn_cast<StoreInst>(Users[i])) {
} else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
// Store must be unreachable or storing Init into the global.
SI->getParent()->getInstList().erase(SI);
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
if (CE->getOpcode() == Instruction::GetElementPtr) {
if (Constant *SubInit = TraverseGEPInitializer(CE, Init))
CleanupConstantGlobalUsers(CE, SubInit);
if (CE->use_empty()) CE->destroyConstant();
}
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
if (Constant *SubInit = TraverseGEPInitializer(GEP, Init))
CleanupConstantGlobalUsers(GEP, SubInit);
if (GEP->use_empty())
GEP->getParent()->getInstList().erase(GEP);
}
}
}
bool Constifier::runOnModule(Module &M) {
bool GlobalOpt::runOnModule(Module &M) {
bool Changed = false;
// As a prepass, delete functions that are trivially dead.
bool LocalChange = true;
while (LocalChange) {
LocalChange = false;
for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
Function *F = FI++;
F->removeDeadConstantUsers();
if (F->use_empty() && (F->hasInternalLinkage() || F->hasWeakLinkage())) {
M.getFunctionList().erase(F);
LocalChange = true;
++NumFnDeleted;
}
}
Changed |= LocalChange;
}
std::set<PHINode*> PHIUsers;
for (Module::giterator GVI = M.gbegin(), E = M.gend(); GVI != E;) {
GlobalVariable *GV = GVI++;
if (!GV->isConstant() && GV->hasInternalLinkage() && GV->hasInitializer()) {
if (!isStoredThrough(GV, PHIUsers)) {
DEBUG(std::cerr << "MARKING CONSTANT: " << *GV << "\n");
GV->setConstant(true);
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV);
// If the global is dead now, just nuke it.
if (GV->use_empty()) {
M.getGlobalList().erase(GV);
++NumDeleted;
}
++NumMarked;
Changed = true;
}
GlobalStatus GS;
PHIUsers.clear();
GV->removeDeadConstantUsers();
if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
// If the global is never loaded (but may be stored to), it is dead.
// Delete it now.
if (!GS.isLoaded) {
DEBUG(std::cerr << "GLOBAL NEVER LOADED: " << *GV);
// Delete any stores we can find to the global. We may not be able to
// make it completely dead though.
CleanupConstantGlobalUsers(GV, GV->getInitializer());
// If the global is dead now, delete it.
if (GV->use_empty()) {
M.getGlobalList().erase(GV);
++NumDeleted;
}
Changed = true;
} else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
DEBUG(std::cerr << "MARKING CONSTANT: " << *GV);
GV->setConstant(true);
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV, GV->getInitializer());
// If the global is dead now, just nuke it.
if (GV->use_empty()) {
M.getGlobalList().erase(GV);
++NumDeleted;
}
++NumMarked;
Changed = true;
} else if (!GS.isNotSuitableForSRA &&
!GV->getInitializer()->getType()->isFirstClassType()) {
//std::cerr << "COULD SRA: " << *GV;
}
}
}
}
return Changed;