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Optimize more linkonce_odr values during LTO.

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When a linkonce_odr value that is on the dso list is not unnamed_addr
we can still look to see if anything is actually using its address. If
not, it is safe to hide it.

This patch implements that by moving GlobalStatus to Transforms/Utils
and using it in Internalize.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193090 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola 2013-10-21 17:14:55 +00:00
parent da39dd30ad
commit 713cab059e
7 changed files with 294 additions and 213 deletions
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82
include/llvm/Transforms/Utils/GlobalStatus.h Normal file
View File

@ -0,0 +1,82 @@
//===- GlobalStatus.h - Compute status info for globals ---------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H
#define LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H
#include "llvm/IR/Instructions.h"
namespace llvm {
class Value;
class Function;
/// 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 isSafeToDestroyConstant(const Constant *C);
/// 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 this info will be
/// accurate.
struct GlobalStatus {
/// True if the global's address is used in a comparison.
bool IsCompared;
/// True if the global is ever loaded. If the global isn't ever loaded it
/// can be deleted.
bool IsLoaded;
/// Keep track of what stores to the global look like.
enum StoredType {
/// There is no store to this global. It can thus be marked constant.
NotStored,
/// This global is stored to, but the only thing stored is the constant it
/// was initialized with. This is only tracked for scalar globals.
InitializerStored,
/// This global is stored to, but only its initializer and one other value
/// is ever stored to it. If this global isStoredOnce, we track the value
/// stored to it in StoredOnceValue below. This is only tracked for scalar
/// globals.
StoredOnce,
/// This global is stored to by multiple values or something else that we
/// cannot track.
Stored
} StoredType;
/// If only one value (besides the initializer constant) is ever stored to
/// this global, keep track of what value it is.
Value *StoredOnceValue;
/// These start out null/false. When the first accessing function is noticed,
/// it is recorded. When a second different accessing function is noticed,
/// HasMultipleAccessingFunctions is set to true.
const Function *AccessingFunction;
bool HasMultipleAccessingFunctions;
/// Set to true if this global has a user that is not an instruction (e.g. a
/// constant expr or GV initializer).
bool HasNonInstructionUser;
/// Set to the strongest atomic ordering requirement.
AtomicOrdering Ordering;
/// 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 analyzeGlobal(const Value *V, GlobalStatus &GS);
GlobalStatus();
};
}
#endif

210
lib/Transforms/IPO/GlobalOpt.cpp
View File

@ -38,6 +38,7 @@
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
#include <algorithm>
using namespace llvm;
@ -60,7 +61,6 @@ STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
namespace {
struct GlobalStatus;
struct GlobalOpt : public ModulePass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetLibraryInfo>();
@ -99,214 +99,8 @@ ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
namespace {
/// 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 this info will be
/// accurate.
struct GlobalStatus {
/// True if the global's address is used in a comparison.
bool IsCompared;
/// True if the global is ever loaded. If the global isn't ever loaded it can
/// be deleted.
bool IsLoaded;
/// Keep track of what stores to the global look like.
///
enum StoredType {
/// There is no store to this global. It can thus be marked constant.
NotStored,
/// This global is stored to, but the only thing stored is the constant it
/// was initialized with. This is only tracked for scalar globals.
InitializerStored,
/// This global is stored to, but only its initializer and one other value
/// is ever stored to it. If this global StoredOnce, we track the value
/// stored to it in StoredOnceValue below. This is only tracked for scalar
/// globals.
StoredOnce,
/// This global is stored to by multiple values or something else that we
/// cannot track.
Stored
} StoredType;
/// StoredOnceValue - If only one value (besides the initializer constant) is
/// ever stored to this global, keep track of what value it is.
Value *StoredOnceValue;
/// AccessingFunction/HasMultipleAccessingFunctions - These start out
/// null/false. When the first accessing function is noticed, it is recorded.
/// When a second different accessing function is noticed,
/// HasMultipleAccessingFunctions is set to true.
const Function *AccessingFunction;
bool HasMultipleAccessingFunctions;
/// HasNonInstructionUser - Set to true if this global has a user that is not
/// an instruction (e.g. a constant expr or GV initializer).
bool HasNonInstructionUser;
/// AtomicOrdering - Set to the strongest atomic ordering requirement.
AtomicOrdering Ordering;
GlobalStatus() : IsCompared(false), IsLoaded(false), StoredType(NotStored),
StoredOnceValue(0), AccessingFunction(0),
HasMultipleAccessingFunctions(false),
HasNonInstructionUser(false), Ordering(NotAtomic) {}
};
}
/// StrongerOrdering - Return the stronger of the two ordering. If the two
/// orderings are acquire and release, then return AcquireRelease.
///
static AtomicOrdering StrongerOrdering(AtomicOrdering X, AtomicOrdering Y) {
if (X == Acquire && Y == Release) return AcquireRelease;
if (Y == Acquire && X == Release) return AcquireRelease;
return (AtomicOrdering)std::max(X, Y);
}
/// 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.
///
static bool isSafeToDestroyConstant(const Constant *C) {
if (isa<GlobalValue>(C))
return false;
for (Value::const_use_iterator UI = C->use_begin(), E = C->use_end(); UI != E;
++UI)
if (const Constant *CU = dyn_cast<Constant>(*UI)) {
if (!isSafeToDestroyConstant(CU))
return false;
} else
return false;
return true;
}
static bool analyzeGlobalAux(const Value *V, GlobalStatus &GS,
SmallPtrSet<const PHINode *, 16> &PHIUsers) {
for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
++UI) {
const User *U = *UI;
if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
GS.HasNonInstructionUser = true;
// If the result of the constantexpr isn't pointer type, then we won't
// know to expect it in various places. Just reject early.
if (!isa<PointerType>(CE->getType())) return true;
if (analyzeGlobalAux(CE, GS, PHIUsers))
return true;
} else if (const Instruction *I = dyn_cast<Instruction>(U)) {
if (!GS.HasMultipleAccessingFunctions) {
const Function *F = I->getParent()->getParent();
if (GS.AccessingFunction == 0)
GS.AccessingFunction = F;
else if (GS.AccessingFunction != F)
GS.HasMultipleAccessingFunctions = true;
}
if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
GS.IsLoaded = true;
// Don't hack on volatile loads.
if (LI->isVolatile()) return true;
GS.Ordering = StrongerOrdering(GS.Ordering, LI->getOrdering());
} else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
// Don't allow a store OF the address, only stores TO the address.
if (SI->getOperand(0) == V) return true;
// Don't hack on volatile stores.
if (SI->isVolatile()) return true;
GS.Ordering = StrongerOrdering(GS.Ordering, SI->getOrdering());
// If this is a direct store to the global (i.e., the global is a scalar
// value, not an aggregate), keep more specific information about
// stores.
if (GS.StoredType != GlobalStatus::Stored) {
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(
SI->getOperand(1))) {
Value *StoredVal = SI->getOperand(0);
if (Constant *C = dyn_cast<Constant>(StoredVal)) {
if (C->isThreadDependent()) {
// The stored value changes between threads; don't track it.
return true;
}
}
if (StoredVal == GV->getInitializer()) {
if (GS.StoredType < GlobalStatus::InitializerStored)
GS.StoredType = GlobalStatus::InitializerStored;
} else if (isa<LoadInst>(StoredVal) &&
cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
if (GS.StoredType < GlobalStatus::InitializerStored)
GS.StoredType = GlobalStatus::InitializerStored;
} else if (GS.StoredType < GlobalStatus::StoredOnce) {
GS.StoredType = GlobalStatus::StoredOnce;
GS.StoredOnceValue = StoredVal;
} else if (GS.StoredType == GlobalStatus::StoredOnce &&
GS.StoredOnceValue == StoredVal) {
// noop.
} else {
GS.StoredType = GlobalStatus::Stored;
}
} else {
GS.StoredType = GlobalStatus::Stored;
}
}
} else if (isa<BitCastInst>(I)) {
if (analyzeGlobalAux(I, GS, PHIUsers))
return true;
} else if (isa<GetElementPtrInst>(I)) {
if (analyzeGlobalAux(I, GS, PHIUsers))
return true;
} else if (isa<SelectInst>(I)) {
if (analyzeGlobalAux(I, GS, PHIUsers))
return true;
} else if (const 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)) // Not already visited.
if (analyzeGlobalAux(I, GS, PHIUsers))
return true;
} else if (isa<CmpInst>(I)) {
GS.IsCompared = true;
} else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) {
if (MTI->isVolatile()) return true;
if (MTI->getArgOperand(0) == V)
GS.StoredType = GlobalStatus::Stored;
if (MTI->getArgOperand(1) == V)
GS.IsLoaded = true;
} else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) {
assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!");
if (MSI->isVolatile()) return true;
GS.StoredType = GlobalStatus::Stored;
} else {
return true; // Any other non-load instruction might take address!
}
} else if (const Constant *C = dyn_cast<Constant>(U)) {
GS.HasNonInstructionUser = true;
// We might have a dead and dangling constant hanging off of here.
if (!isSafeToDestroyConstant(C))
return true;
} else {
GS.HasNonInstructionUser = true;
// Otherwise must be some other user.
return true;
}
}
return false;
}
/// 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 analyzeGlobal(const Value *V, GlobalStatus &GS) {
SmallPtrSet<const PHINode *, 16> PHIUsers;
return analyzeGlobalAux(V, GS, PHIUsers);
}
/// isLeakCheckerRoot - Is this global variable possibly used by a leak checker
@ -1927,7 +1721,7 @@ bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
GlobalStatus GS;
if (analyzeGlobal(GV, GS))
if (GlobalStatus::analyzeGlobal(GV, GS))
return false;
if (!GS.IsCompared && !GV->hasUnnamedAddr()) {

21
lib/Transforms/IPO/Internalize.cpp
View File

@ -11,6 +11,19 @@
// If the function or variable is not in the list of external names given to
// the pass it is marked as internal.
//
// This transformation would not be legal or profitable in a regular
// compilation, but it gets extra information from the linker about what is safe
// or profitable.
//
// As an example of a normally illegal transformation: Internalizing a function
// with external linkage. Only if we are told it is only used from within this
// module, it is safe to do it.
//
// On the profitability side: It is always legal to internalize a linkonce_odr
// whose address is not used. Doing so normally would introduce code bloat, but
// if we are told by the linker that the only use of this would be for a
// DSO symbol table, it is profitable to hide it.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "internalize"
@ -23,6 +36,7 @@
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
#include <fstream>
#include <set>
@ -142,8 +156,11 @@ static bool shouldInternalize(const GlobalValue &GV,
if (GV.hasUnnamedAddr())
return true;
// FIXME: Check if the address is used.
return false;
GlobalStatus GS;
if (GlobalStatus::analyzeGlobal(&GV, GS))
return false;
return !GS.IsCompared;
}
bool InternalizePass::runOnModule(Module &M) {

1
lib/Transforms/Utils/CMakeLists.txt
View File

@ -8,6 +8,7 @@ add_llvm_library(LLVMTransformUtils
CmpInstAnalysis.cpp
CodeExtractor.cpp
DemoteRegToStack.cpp
GlobalStatus.cpp
InlineFunction.cpp
InstructionNamer.cpp
IntegerDivision.cpp

178
lib/Transforms/Utils/GlobalStatus.cpp Normal file
View File

@ -0,0 +1,178 @@
//===-- GlobalStatus.cpp - Compute status info for globals -----------------==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
using namespace llvm;
/// Return the stronger of the two ordering. If the two orderings are acquire
/// and release, then return AcquireRelease.
///
static AtomicOrdering strongerOrdering(AtomicOrdering X, AtomicOrdering Y) {
if (X == Acquire && Y == Release)
return AcquireRelease;
if (Y == Acquire && X == Release)
return AcquireRelease;
return (AtomicOrdering)std::max(X, Y);
}
/// 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 llvm::isSafeToDestroyConstant(const Constant *C) {
if (isa<GlobalValue>(C))
return false;
for (Value::const_use_iterator UI = C->use_begin(), E = C->use_end(); UI != E;
++UI)
if (const Constant *CU = dyn_cast<Constant>(*UI)) {
if (!isSafeToDestroyConstant(CU))
return false;
} else
return false;
return true;
}
static bool analyzeGlobalAux(const Value *V, GlobalStatus &GS,
SmallPtrSet<const PHINode *, 16> &PhiUsers) {
for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
++UI) {
const User *U = *UI;
if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
GS.HasNonInstructionUser = true;
// If the result of the constantexpr isn't pointer type, then we won't
// know to expect it in various places. Just reject early.
if (!isa<PointerType>(CE->getType()))
return true;
if (analyzeGlobalAux(CE, GS, PhiUsers))
return true;
} else if (const Instruction *I = dyn_cast<Instruction>(U)) {
if (!GS.HasMultipleAccessingFunctions) {
const Function *F = I->getParent()->getParent();
if (GS.AccessingFunction == 0)
GS.AccessingFunction = F;
else if (GS.AccessingFunction != F)
GS.HasMultipleAccessingFunctions = true;
}
if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
GS.IsLoaded = true;
// Don't hack on volatile loads.
if (LI->isVolatile())
return true;
GS.Ordering = strongerOrdering(GS.Ordering, LI->getOrdering());
} else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
// Don't allow a store OF the address, only stores TO the address.
if (SI->getOperand(0) == V)
return true;
// Don't hack on volatile stores.
if (SI->isVolatile())
return true;
GS.Ordering = strongerOrdering(GS.Ordering, SI->getOrdering());
// If this is a direct store to the global (i.e., the global is a scalar
// value, not an aggregate), keep more specific information about
// stores.
if (GS.StoredType != GlobalStatus::Stored) {
if (const GlobalVariable *GV =
dyn_cast<GlobalVariable>(SI->getOperand(1))) {
Value *StoredVal = SI->getOperand(0);
if (Constant *C = dyn_cast<Constant>(StoredVal)) {
if (C->isThreadDependent()) {
// The stored value changes between threads; don't track it.
return true;
}
}
if (StoredVal == GV->getInitializer()) {
if (GS.StoredType < GlobalStatus::InitializerStored)
GS.StoredType = GlobalStatus::InitializerStored;
} else if (isa<LoadInst>(StoredVal) &&
cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
if (GS.StoredType < GlobalStatus::InitializerStored)
GS.StoredType = GlobalStatus::InitializerStored;
} else if (GS.StoredType < GlobalStatus::StoredOnce) {
GS.StoredType = GlobalStatus::StoredOnce;
GS.StoredOnceValue = StoredVal;
} else if (GS.StoredType == GlobalStatus::StoredOnce &&
GS.StoredOnceValue == StoredVal) {
// noop.
} else {
GS.StoredType = GlobalStatus::Stored;
}
} else {
GS.StoredType = GlobalStatus::Stored;
}
}
} else if (isa<BitCastInst>(I)) {
if (analyzeGlobalAux(I, GS, PhiUsers))
return true;
} else if (isa<GetElementPtrInst>(I)) {
if (analyzeGlobalAux(I, GS, PhiUsers))
return true;
} else if (isa<SelectInst>(I)) {
if (analyzeGlobalAux(I, GS, PhiUsers))
return true;
} else if (const 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)) // Not already visited.
if (analyzeGlobalAux(I, GS, PhiUsers))
return true;
} else if (isa<CmpInst>(I)) {
GS.IsCompared = true;
} else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) {
if (MTI->isVolatile())
return true;
if (MTI->getArgOperand(0) == V)
GS.StoredType = GlobalStatus::Stored;
if (MTI->getArgOperand(1) == V)
GS.IsLoaded = true;
} else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) {
assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!");
if (MSI->isVolatile())
return true;
GS.StoredType = GlobalStatus::Stored;
} else {
return true; // Any other non-load instruction might take address!
}
} else if (const Constant *C = dyn_cast<Constant>(U)) {
GS.HasNonInstructionUser = true;
// We might have a dead and dangling constant hanging off of here.
if (!isSafeToDestroyConstant(C))
return true;
} else {
GS.HasNonInstructionUser = true;
// Otherwise must be some other user.
return true;
}
}
return false;
}
bool GlobalStatus::analyzeGlobal(const Value *V, GlobalStatus &GS) {
SmallPtrSet<const PHINode *, 16> PhiUsers;
return analyzeGlobalAux(V, GS, PhiUsers);
}
GlobalStatus::GlobalStatus()
: IsCompared(false), IsLoaded(false), StoredType(NotStored),
StoredOnceValue(0), AccessingFunction(0),
HasMultipleAccessingFunctions(false), HasNonInstructionUser(false),
Ordering(NotAtomic) {}

3
test/LTO/cfi_endproc.ll
View File

@ -29,6 +29,9 @@ define i32 @main(i32 %argc, i8** %argv) {
; RUN: llvm-nm %t | FileCheck %s -check-prefix=ZED1_AND_ZED2
; ZED1_AND_ZED2: V zed1
@zed1 = linkonce_odr global i32 42
define i32* @get_zed1() {
ret i32* @zed1
}
; ZED1_AND_ZED2: d zed2
@zed2 = linkonce_odr unnamed_addr global i32 42

12
test/Transforms/Internalize/lists.ll
View File

@ -15,7 +15,7 @@
; Put zed1 and zed2 in the symbol table. If the address is not relevant, we
; internalize them.
; RUN: opt < %s -internalize -internalize-dso-list zed1,zed2 -S | FileCheck --check-prefix=ZED1_AND_ZED2 %s
; RUN: opt < %s -internalize -internalize-dso-list zed1,zed2,zed3 -S | FileCheck --check-prefix=ZEDS %s
; ALL: @i = internal global
; FOO_AND_J: @i = internal global
@ -29,12 +29,18 @@
; FOO_J_AND_BAR: @j = global
@j = global i32 0
; ZED1_AND_ZED2: @zed1 = linkonce_odr global i32 42
; ZEDS: @zed1 = internal global i32 42
@zed1 = linkonce_odr global i32 42
; ZED1_AND_ZED2: @zed2 = internal unnamed_addr global i32 42
; ZEDS: @zed2 = internal unnamed_addr global i32 42
@zed2 = linkonce_odr unnamed_addr global i32 42
; ZEDS: @zed3 = linkonce_odr global i32 42
@zed3 = linkonce_odr global i32 42
define i32* @get_zed3() {
ret i32* @zed3
}
; ALL: define internal void @main() {
; FOO_AND_J: define internal void @main() {
; FOO_AND_BAR: define internal void @main() {