[llvm-commits] CVS: llvm/lib/Transforms/IPO/GlobalConstifier.cpp
Chris Lattner
lattner at cs.uiuc.edu
Wed Oct 6 21:16:44 PDT 2004
Changes in directory llvm/lib/Transforms/IPO:
GlobalConstifier.cpp updated: 1.9 -> 1.10
---
Log message:
* Rename pass to globalopt, since we do more than just constify
* 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.
---
Diffs of the changes: (+183 -80)
Index: llvm/lib/Transforms/IPO/GlobalConstifier.cpp
diff -u llvm/lib/Transforms/IPO/GlobalConstifier.cpp:1.9 llvm/lib/Transforms/IPO/GlobalConstifier.cpp:1.10
--- llvm/lib/Transforms/IPO/GlobalConstifier.cpp:1.9 Wed Oct 6 15:57:02 2004
+++ llvm/lib/Transforms/IPO/GlobalConstifier.cpp Wed Oct 6 23:16:33 2004
@@ -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");
-}
-
-ModulePass *llvm::createGlobalConstifierPass() { return new Constifier(); }
-
-/// 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();
+ RegisterOpt<GlobalOpt> X("globalopt", "Global Variable Optimizer");
}
+ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
-/// isStoredThrough - Return false if the specified pointer is provably never
-/// stored through. If we can't tell, we must conservatively assume it might.
+/// 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) {}
+};
+
+/// 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 @@
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;
+ 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;
}
-
- ++NumMarked;
- Changed = true;
}
- PHIUsers.clear();
}
}
return Changed;
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