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With this patch, the LowerGC transformation becomes the

Browse Source 
ShadowStackCollector, which additionally has reduced overhead with
no sacrifice in portability.

Considering a function @fun with 8 loop-local roots,
ShadowStackCollector introduces the following overhead
(x86):

; shadowstack prologue
        movl    L_llvm_gc_root_chain$non_lazy_ptr, %eax
        movl    (%eax), %ecx
        movl    $___gc_fun, 20(%esp)
        movl    $0, 24(%esp)
        movl    $0, 28(%esp)
        movl    $0, 32(%esp)
        movl    $0, 36(%esp)
        movl    $0, 40(%esp)
        movl    $0, 44(%esp)
        movl    $0, 48(%esp)
        movl    $0, 52(%esp)
        movl    %ecx, 16(%esp)
        leal    16(%esp), %ecx
        movl    %ecx, (%eax)

; shadowstack loop overhead
        (none)

; shadowstack epilogue
        movl    48(%esp), %edx
        movl    %edx, (%ecx)

; shadowstack metadata
        .align  3
___gc_fun:                              # __gc_fun
        .long   8
        .space  4

In comparison to LowerGC:

; lowergc prologue
        movl    L_llvm_gc_root_chain$non_lazy_ptr, %eax
        movl    (%eax), %ecx
        movl    %ecx, 48(%esp)
        movl    $8, 52(%esp)
        movl    $0, 60(%esp)
        movl    $0, 56(%esp)
        movl    $0, 68(%esp)
        movl    $0, 64(%esp)
        movl    $0, 76(%esp)
        movl    $0, 72(%esp)
        movl    $0, 84(%esp)
        movl    $0, 80(%esp)
        movl    $0, 92(%esp)
        movl    $0, 88(%esp)
        movl    $0, 100(%esp)
        movl    $0, 96(%esp)
        movl    $0, 108(%esp)
        movl    $0, 104(%esp)
        movl    $0, 116(%esp)
        movl    $0, 112(%esp)

; lowergc loop overhead
        leal    44(%esp), %eax
        movl    %eax, 56(%esp)
        leal    40(%esp), %eax
        movl    %eax, 64(%esp)
        leal    36(%esp), %eax
        movl    %eax, 72(%esp)
        leal    32(%esp), %eax
        movl    %eax, 80(%esp)
        leal    28(%esp), %eax
        movl    %eax, 88(%esp)
        leal    24(%esp), %eax
        movl    %eax, 96(%esp)
        leal    20(%esp), %eax
        movl    %eax, 104(%esp)
        leal    16(%esp), %eax
        movl    %eax, 112(%esp)

; lowergc epilogue
        movl    48(%esp), %edx
        movl    %edx, (%ecx)

; lowergc metadata
        (none)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45670 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Gordon Henriksen 2008-01-07 01:30:53 +00:00
parent ce2247755e
commit 8fa8929177
7 changed files with 477 additions and 372 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/llvm/CodeGen/LinkAllCodegenComponents.h
View File

@ -17,6 +17,7 @@
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/CodeGen/Collectors.h"
namespace {
struct ForceCodegenLinking {
@ -35,6 +36,8 @@ namespace {
(void) llvm::createSimpleRegisterCoalescer();
(void) llvm::createShadowStackCollector();
(void) llvm::createBURRListDAGScheduler(NULL, NULL, NULL);
(void) llvm::createTDRRListDAGScheduler(NULL, NULL, NULL);
(void) llvm::createTDListDAGScheduler(NULL, NULL, NULL);

1
include/llvm/LinkAllPasses.h
View File

@ -84,7 +84,6 @@ namespace {
(void) llvm::createLoopRotatePass();
(void) llvm::createLoopIndexSplitPass();
(void) llvm::createLowerAllocationsPass();
(void) llvm::createLowerGCPass();
(void) llvm::createLowerInvokePass();
(void) llvm::createLowerPackedPass();
(void) llvm::createLowerSelectPass();

7
include/llvm/Transforms/Scalar.h
View File

@ -294,13 +294,6 @@ FunctionPass *createLowerPackedPass();
FunctionPass *createLowerInvokePass(const TargetLowering *TLI = NULL);
extern const PassInfo *LowerInvokePassID;
//===----------------------------------------------------------------------===//
//
// LowerGCPass - This function returns an instance of the "lowergc" pass, which
// lowers garbage collection intrinsics to normal LLVM code.
//
FunctionPass *createLowerGCPass();
//===----------------------------------------------------------------------===//
//
// BlockPlacement - This pass reorders basic blocks in order to increase the

441
lib/CodeGen/ShadowStackCollector.cpp Normal file
View File

@ -0,0 +1,441 @@
//===-- ShadowStackCollector.cpp - GC support for uncooperative targets ---===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements lowering for the llvm.gc* intrinsics for targets that do
// not natively support them (which includes the C backend). Note that the code
// generated is not quite as efficient as collectors which generate stack maps
// to identify roots.
//
// This pass implements the code transformation described in this paper:
// "Accurate Garbage Collection in an Uncooperative Environment"
// Fergus Henderson, ISMM, 2002
//
// In runtime/GC/SemiSpace.cpp is a prototype runtime which is compatible with
// this collector.
//
// In order to support this particular transformation, all stack roots are
// coallocated in the stack. This allows a fully target-independent stack map
// while introducing only minor runtime overhead.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "shadowstackgc"
#include "llvm/CodeGen/Collectors.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/CodeGen/Collector.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/LLVMBuilder.h"
#include "llvm/Analysis/Verifier.h"
#include <cstdlib>
using namespace llvm;
namespace {
class VISIBILITY_HIDDEN ShadowStackCollector : public Collector {
/// RootChain - This is the global linked-list that contains the chain of GC
/// roots.
GlobalVariable *Head;
/// StackEntryTy - Abstract type of a link in the shadow stack.
///
const StructType *StackEntryTy;
/// Roots - GC roots in the current function. Each is a pair of the
/// intrinsic call and its corresponding alloca.
std::vector<std::pair<CallInst*,AllocaInst*> > Roots;
public:
ShadowStackCollector();
bool initializeCustomLowering(Module &M);
bool performCustomLowering(Function &F);
private:
bool IsNullValue(Value *V);
Constant *GetFrameMap(Function &F);
const Type* GetConcreteStackEntryType(Function &F);
void CollectRoots(Function &F);
static GetElementPtrInst *CreateGEP(LLVMBuilder &B, Value *BasePtr,
int Idx1, const char *Name);
static GetElementPtrInst *CreateGEP(LLVMBuilder &B, Value *BasePtr,
int Idx1, int Idx2, const char *Name);
};
CollectorRegistry::Add<ShadowStackCollector>
Y("shadow-stack",
"Very portable collector for uncooperative code generators");
/// EscapeEnumerator - This is a little algorithm to find all escape points
/// from a function so that "finally"-style code can be inserted. In addition
/// to finding the existing return and unwind instructions, it also (if
/// necessary) transforms any call instructions into invokes and sends them to
/// a landing pad.
///
/// It's wrapped up in a state machine using the same transform C# uses for
/// 'yield return' enumerators, This transform allows it to be non-allocating.
class VISIBILITY_HIDDEN EscapeEnumerator {
Function &F;
const char *CleanupBBName;
// State.
int State;
Function::iterator StateBB, StateE;
LLVMBuilder Builder;
public:
EscapeEnumerator(Function &F, const char *N = "cleanup")
: F(F), CleanupBBName(N), State(0) {}
LLVMBuilder *Next() {
switch (State) {
default:
return 0;
case 0:
StateBB = F.begin();
StateE = F.end();
State = 1;
case 1:
// Find all 'return' and 'unwind' instructions.
while (StateBB != StateE) {
BasicBlock *CurBB = StateBB++;
// Branches and invokes do not escape, only unwind and return do.
TerminatorInst *TI = CurBB->getTerminator();
if (!isa<UnwindInst>(TI) && !isa<ReturnInst>(TI))
continue;
Builder.SetInsertPoint(TI->getParent(), TI);
return &Builder;
}
State = 2;
// Find all 'call' instructions.
SmallVector<Instruction*,16> Calls;
for (Function::iterator BB = F.begin(),
E = F.end(); BB != E; ++BB)
for (BasicBlock::iterator II = BB->begin(),
EE = BB->end(); II != EE; ++II)
if (CallInst *CI = dyn_cast<CallInst>(II))
if (!CI->getCalledFunction() ||
!CI->getCalledFunction()->getIntrinsicID())
Calls.push_back(CI);
if (Calls.empty())
return 0;
// Create a cleanup block.
BasicBlock *CleanupBB = new BasicBlock(CleanupBBName, &F);
UnwindInst *UI = new UnwindInst(CleanupBB);
// Transform the 'call' instructions into 'invoke's branching to the
// cleanup block. Go in reverse order to make prettier BB names.
SmallVector<Value*,16> Args;
for (unsigned I = Calls.size(); I != 0; ) {
CallInst *CI = cast<CallInst>(Calls[--I]);
// Split the basic block containing the function call.
BasicBlock *CallBB = CI->getParent();
BasicBlock *NewBB =
CallBB->splitBasicBlock(CI, CallBB->getName() + ".cont");
// Remove the unconditional branch inserted at the end of CallBB.
CallBB->getInstList().pop_back();
NewBB->getInstList().remove(CI);
// Create a new invoke instruction.
Args.clear();
Args.append(CI->op_begin() + 1, CI->op_end());
InvokeInst *II = new InvokeInst(CI->getOperand(0),
NewBB, CleanupBB,
Args.begin(), Args.end(),
CI->getName(), CallBB);
II->setCallingConv(CI->getCallingConv());
II->setParamAttrs(CI->getParamAttrs());
CI->replaceAllUsesWith(II);
delete CI;
}
Builder.SetInsertPoint(UI->getParent(), UI);
return &Builder;
}
}
};
}
// -----------------------------------------------------------------------------
Collector *llvm::createShadowStackCollector() {
return new ShadowStackCollector();
}
ShadowStackCollector::ShadowStackCollector() : Head(0), StackEntryTy(0) {
InitRoots = true;
CustomRoots = true;
}
Constant *ShadowStackCollector::GetFrameMap(Function &F) {
// doInitialization creates the abstract type of this value.
Type *VoidPtr = PointerType::getUnqual(Type::Int8Ty);
// Truncate the ShadowStackDescriptor if some metadata is null.
unsigned NumMeta = 0;
SmallVector<Constant*,16> Metadata;
for (unsigned I = 0; I != Roots.size(); ++I) {
Constant *C = cast<Constant>(Roots[I].first->getOperand(2));
if (!C->isNullValue())
NumMeta = I + 1;
Metadata.push_back(ConstantExpr::getBitCast(C, VoidPtr));
}
Constant *BaseElts[] = {
ConstantInt::get(Type::Int32Ty, Roots.size(), false),
ConstantInt::get(Type::Int32Ty, NumMeta, false),
};
Constant *DescriptorElts[] = {
ConstantStruct::get(BaseElts, 2),
ConstantArray::get(ArrayType::get(VoidPtr, NumMeta),
Metadata.begin(), NumMeta)
};
Constant *FrameMap = ConstantStruct::get(DescriptorElts, 2);
std::string TypeName("gc_map.");
TypeName += utostr(NumMeta);
F.getParent()->addTypeName(TypeName, FrameMap->getType());
// FIXME: Is this actually dangerous as WritingAnLLVMPass.html claims? Seems
// that, short of multithreaded LLVM, it should be safe; all that is
// necessary is that a simple Module::iterator loop not be invalidated.
// Appending to the GlobalVariable list is safe in that sense.
//
// All of the output passes emit globals last. The ExecutionEngine
// explicitly supports adding globals to the module after
// initialization.
//
// Still, if it isn't deemed acceptable, then this transformation needs
// to be a ModulePass (which means it cannot be in the 'llc' pipeline
// (which uses a FunctionPassManager (which segfaults (not asserts) if
// provided a ModulePass))).
Constant *GV = new GlobalVariable(FrameMap->getType(), true,
GlobalVariable::InternalLinkage,
FrameMap, "__gc_" + F.getName(),
F.getParent());
Constant *GEPIndices[2] = { ConstantInt::get(Type::Int32Ty, 0),
ConstantInt::get(Type::Int32Ty, 0) };
return ConstantExpr::getGetElementPtr(GV, GEPIndices, 2);
}
const Type* ShadowStackCollector::GetConcreteStackEntryType(Function &F) {
// doInitialization creates the generic version of this type.
std::vector<const Type*> EltTys;
EltTys.push_back(StackEntryTy);
for (size_t I = 0; I != Roots.size(); I++)
EltTys.push_back(Roots[I].second->getAllocatedType());
Type *Ty = StructType::get(EltTys);
std::string TypeName("gc_stackentry.");
TypeName += F.getName();
F.getParent()->addTypeName(TypeName, Ty);
return Ty;
}
/// doInitialization - If this module uses the GC intrinsics, find them now. If
/// not, exit fast.
bool ShadowStackCollector::initializeCustomLowering(Module &M) {
// struct FrameMap {
// int32_t NumRoots; // Number of roots in stack frame.
// int32_t NumMeta; // Number of metadata descriptors. May be < NumRoots.
// void *Meta[]; // May be absent for roots without metadata.
// };
std::vector<const Type*> EltTys;
EltTys.push_back(Type::Int32Ty); // 32 bits is ok up to a 32GB stack frame. :)
EltTys.push_back(Type::Int32Ty); // Specifies length of variable length array.
StructType *FrameMapTy = StructType::get(EltTys);
M.addTypeName("gc_map", FrameMapTy);
PointerType *FrameMapPtrTy = PointerType::getUnqual(FrameMapTy);
// struct StackEntry {
// ShadowStackEntry *Next; // Caller's stack entry.
// FrameMap *Map; // Pointer to constant FrameMap.
// void *Roots[]; // Stack roots (in-place array, so we pretend).
// };
OpaqueType *RecursiveTy = OpaqueType::get();
EltTys.clear();
EltTys.push_back(PointerType::getUnqual(RecursiveTy));
EltTys.push_back(FrameMapPtrTy);
PATypeHolder LinkTyH = StructType::get(EltTys);
RecursiveTy->refineAbstractTypeTo(LinkTyH.get());
StackEntryTy = cast<StructType>(LinkTyH.get());
const PointerType *StackEntryPtrTy = PointerType::getUnqual(StackEntryTy);
M.addTypeName("gc_stackentry", LinkTyH.get()); // FIXME: Is this safe from
// a FunctionPass?
// Get the root chain if it already exists.
Head = M.getGlobalVariable("llvm_gc_root_chain");
if (!Head) {
// If the root chain does not exist, insert a new one with linkonce
// linkage!
Head = new GlobalVariable(StackEntryPtrTy, false,
GlobalValue::LinkOnceLinkage,
Constant::getNullValue(StackEntryPtrTy),
"llvm_gc_root_chain", &M);
} else if (Head->hasExternalLinkage() && Head->isDeclaration()) {
Head->setInitializer(Constant::getNullValue(StackEntryPtrTy));
Head->setLinkage(GlobalValue::LinkOnceLinkage);
}
return true;
}
bool ShadowStackCollector::IsNullValue(Value *V) {
if (Constant *C = dyn_cast<Constant>(V))
return C->isNullValue();
return false;
}
void ShadowStackCollector::CollectRoots(Function &F) {
// FIXME: Account for original alignment. Could fragment the root array.
// Approach 1: Null initialize empty slots at runtime. Yuck.
// Approach 2: Emit a map of the array instead of just a count.
assert(Roots.empty() && "Not cleaned up?");
SmallVector<std::pair<CallInst*,AllocaInst*>,16> MetaRoots;
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;)
if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++))
if (Function *F = CI->getCalledFunction())
if (F->getIntrinsicID() == Intrinsic::gcroot) {
std::pair<CallInst*,AllocaInst*> Pair = std::make_pair(
CI, cast<AllocaInst>(
IntrinsicInst::StripPointerCasts(CI->getOperand(1))));
if (IsNullValue(CI->getOperand(2)))
Roots.push_back(Pair);
else
MetaRoots.push_back(Pair);
}
// Number roots with metadata (usually empty) at the beginning, so that the
// FrameMap::Meta array can be elided.
Roots.insert(Roots.begin(), MetaRoots.begin(), MetaRoots.end());
}
GetElementPtrInst *
ShadowStackCollector::CreateGEP(LLVMBuilder &B, Value *BasePtr,
int Idx, int Idx2, const char *Name) {
Value *Indices[] = { ConstantInt::get(Type::Int32Ty, 0),
ConstantInt::get(Type::Int32Ty, Idx),
ConstantInt::get(Type::Int32Ty, Idx2) };
return B.CreateGEP(BasePtr, Indices, Indices + 3, Name);
}
GetElementPtrInst *
ShadowStackCollector::CreateGEP(LLVMBuilder &B, Value *BasePtr,
int Idx, const char *Name) {
Value *Indices[] = { ConstantInt::get(Type::Int32Ty, 0),
ConstantInt::get(Type::Int32Ty, Idx) };
return B.CreateGEP(BasePtr, Indices, Indices + 2, Name);
}
/// runOnFunction - Insert code to maintain the shadow stack.
bool ShadowStackCollector::performCustomLowering(Function &F) {
// Find calls to llvm.gcroot.
CollectRoots(F);
// If there are no roots in this function, then there is no need to add a
// stack map entry for it.
if (Roots.empty())
return false;
// Build the constant map and figure the type of the shadow stack entry.
Value *FrameMap = GetFrameMap(F);
const Type *ConcreteStackEntryTy = GetConcreteStackEntryType(F);
// Build the shadow stack entry at the very start of the function.
BasicBlock::iterator IP = F.getEntryBlock().begin();
LLVMBuilder AtEntry(IP->getParent(), IP);
Instruction *StackEntry = AtEntry.CreateAlloca(ConcreteStackEntryTy, 0,
"gc_frame");
while (isa<AllocaInst>(IP)) ++IP;
AtEntry.SetInsertPoint(IP->getParent(), IP);
// Initialize the map pointer and load the current head of the shadow stack.
Instruction *CurrentHead = AtEntry.CreateLoad(Head, "gc_currhead");
Instruction *EntryMapPtr = CreateGEP(AtEntry, StackEntry,0,1,"gc_frame.map");
AtEntry.CreateStore(FrameMap, EntryMapPtr);
// After all the allocas...
for (unsigned I = 0, E = Roots.size(); I != E; ++I) {
// For each root, find the corresponding slot in the aggregate...
Value *SlotPtr = CreateGEP(AtEntry, StackEntry, 1 + I, "gc_root");
// And use it in lieu of the alloca.
AllocaInst *OriginalAlloca = Roots[I].second;
SlotPtr->takeName(OriginalAlloca);
OriginalAlloca->replaceAllUsesWith(SlotPtr);
}
// Move past the original stores inserted by Collector::InitRoots. This isn't
// really necessary (the collector would never see the intermediate state),
// but it's nicer not to push the half-initialized entry onto the stack.
while (isa<StoreInst>(IP)) ++IP;
AtEntry.SetInsertPoint(IP->getParent(), IP);
// Push the entry onto the shadow stack.
Instruction *EntryNextPtr = CreateGEP(AtEntry,StackEntry,0,0,"gc_frame.next");
Instruction *NewHeadVal = CreateGEP(AtEntry,StackEntry, 0, "gc_newhead");
AtEntry.CreateStore(CurrentHead, EntryNextPtr);
AtEntry.CreateStore(NewHeadVal, Head);
// For each instruction that escapes...
EscapeEnumerator EE(F, "gc_cleanup");
while (LLVMBuilder *AtExit = EE.Next()) {
// Pop the entry from the shadow stack. Don't reuse CurrentHead from
// AtEntry, since that would make the value live for the entire function.
Instruction *EntryNextPtr2 = CreateGEP(*AtExit, StackEntry, 0, 0,
"gc_frame.next");
Value *SavedHead = AtExit->CreateLoad(EntryNextPtr2, "gc_savedhead");
AtExit->CreateStore(SavedHead, Head);
}
// Delete the original allocas (which are no longer used) and the intrinsic
// calls (which are no longer valid). Doing this last avoids invalidating
// iterators.
for (unsigned I = 0, E = Roots.size(); I != E; ++I) {
Roots[I].first->eraseFromParent();
Roots[I].second->eraseFromParent();
}
F.dump();
Roots.clear();
return true;
}

350
lib/Transforms/Scalar/LowerGC.cpp
View File

@ -1,350 +0,0 @@
//===-- LowerGC.cpp - Provide GC support for targets that don't -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements lowering for the llvm.gc* intrinsics for targets that do
// not natively support them (which includes the C backend). Note that the code
// generated is not as efficient as it would be for targets that natively
// support the GC intrinsics, but it is useful for getting new targets
// up-and-running quickly.
//
// This pass implements the code transformation described in this paper:
// "Accurate Garbage Collection in an Uncooperative Environment"
// Fergus Henderson, ISMM, 2002
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "lowergc"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/Compiler.h"
#include "llvm/ADT/SmallVector.h"
using namespace llvm;
namespace {
class VISIBILITY_HIDDEN LowerGC : public FunctionPass {
/// GCRootInt, GCReadInt, GCWriteInt - The function prototypes for the
/// llvm.gcread/llvm.gcwrite/llvm.gcroot intrinsics.
Function *GCRootInt, *GCReadInt, *GCWriteInt;
/// GCRead/GCWrite - These are the functions provided by the garbage
/// collector for read/write barriers.
Constant *GCRead, *GCWrite;
/// RootChain - This is the global linked-list that contains the chain of GC
/// roots.
GlobalVariable *RootChain;
/// MainRootRecordType - This is the type for a function root entry if it
/// had zero roots.
const Type *MainRootRecordType;
public:
static char ID; // Pass identification, replacement for typeid
LowerGC() : FunctionPass((intptr_t)&ID),
GCRootInt(0), GCReadInt(0), GCWriteInt(0),
GCRead(0), GCWrite(0), RootChain(0), MainRootRecordType(0) {}
virtual bool doInitialization(Module &M);
virtual bool runOnFunction(Function &F);
private:
const StructType *getRootRecordType(unsigned NumRoots);
};
char LowerGC::ID = 0;
RegisterPass<LowerGC>
X("lowergc", "Lower GC intrinsics, for GCless code generators");
}
/// createLowerGCPass - This function returns an instance of the "lowergc"
/// pass, which lowers garbage collection intrinsics to normal LLVM code.
FunctionPass *llvm::createLowerGCPass() {
return new LowerGC();
}
/// getRootRecordType - This function creates and returns the type for a root
/// record containing 'NumRoots' roots.
const StructType *LowerGC::getRootRecordType(unsigned NumRoots) {
// Build a struct that is a type used for meta-data/root pairs.
std::vector<const Type *> ST;
ST.push_back(GCRootInt->getFunctionType()->getParamType(0));
ST.push_back(GCRootInt->getFunctionType()->getParamType(1));
StructType *PairTy = StructType::get(ST);
// Build the array of pairs.
ArrayType *PairArrTy = ArrayType::get(PairTy, NumRoots);
// Now build the recursive list type.
PATypeHolder RootListH =
MainRootRecordType ? (Type*)MainRootRecordType : (Type*)OpaqueType::get();
ST.clear();
ST.push_back(PointerType::getUnqual(RootListH)); // Prev pointer
ST.push_back(Type::Int32Ty); // NumElements in array
ST.push_back(PairArrTy); // The pairs
StructType *RootList = StructType::get(ST);
if (MainRootRecordType)
return RootList;
assert(NumRoots == 0 && "The main struct type should have zero entries!");
cast<OpaqueType>((Type*)RootListH.get())->refineAbstractTypeTo(RootList);
MainRootRecordType = RootListH;
return cast<StructType>(RootListH.get());
}
/// doInitialization - If this module uses the GC intrinsics, find them now. If
/// not, this pass does not do anything.
bool LowerGC::doInitialization(Module &M) {
GCRootInt = M.getFunction("llvm.gcroot");
GCReadInt = M.getFunction("llvm.gcread");
GCWriteInt = M.getFunction("llvm.gcwrite");
if (!GCRootInt && !GCReadInt && !GCWriteInt) return false;
PointerType *VoidPtr = PointerType::getUnqual(Type::Int8Ty);
PointerType *VoidPtrPtr = PointerType::getUnqual(VoidPtr);
// If the program is using read/write barriers, find the implementations of
// them from the GC runtime library.
if (GCReadInt) // Make: sbyte* %llvm_gc_read(sbyte**)
GCRead = M.getOrInsertFunction("llvm_gc_read", VoidPtr, VoidPtr, VoidPtrPtr,
(Type *)0);
if (GCWriteInt) // Make: void %llvm_gc_write(sbyte*, sbyte**)
GCWrite = M.getOrInsertFunction("llvm_gc_write", Type::VoidTy,
VoidPtr, VoidPtr, VoidPtrPtr, (Type *)0);
// If the program has GC roots, get or create the global root list.
if (GCRootInt) {
const StructType *RootListTy = getRootRecordType(0);
const Type *PRLTy = PointerType::getUnqual(RootListTy);
M.addTypeName("llvm_gc_root_ty", RootListTy);
// Get the root chain if it already exists.
RootChain = M.getGlobalVariable("llvm_gc_root_chain", PRLTy);
if (RootChain == 0) {
// If the root chain does not exist, insert a new one with linkonce
// linkage!
RootChain = new GlobalVariable(PRLTy, false,
GlobalValue::LinkOnceLinkage,
Constant::getNullValue(PRLTy),
"llvm_gc_root_chain", &M);
} else if (RootChain->hasExternalLinkage() && RootChain->isDeclaration()) {
RootChain->setInitializer(Constant::getNullValue(PRLTy));
RootChain->setLinkage(GlobalValue::LinkOnceLinkage);
}
}
return true;
}
/// Coerce - If the specified operand number of the specified instruction does
/// not have the specified type, insert a cast. Note that this only uses BitCast
/// because the types involved are all pointers.
static void Coerce(Instruction *I, unsigned OpNum, Type *Ty) {
if (I->getOperand(OpNum)->getType() != Ty) {
if (Constant *C = dyn_cast<Constant>(I->getOperand(OpNum)))
I->setOperand(OpNum, ConstantExpr::getBitCast(C, Ty));
else {
CastInst *CI = new BitCastInst(I->getOperand(OpNum), Ty, "", I);
I->setOperand(OpNum, CI);
}
}
}
/// runOnFunction - If the program is using GC intrinsics, replace any
/// read/write intrinsics with the appropriate read/write barrier calls, then
/// inline them. Finally, build the data structures for
bool LowerGC::runOnFunction(Function &F) {
// Quick exit for programs that are not using GC mechanisms.
if (!GCRootInt && !GCReadInt && !GCWriteInt) return false;
PointerType *VoidPtr = PointerType::getUnqual(Type::Int8Ty);
PointerType *VoidPtrPtr = PointerType::getUnqual(VoidPtr);
// If there are read/write barriers in the program, perform a quick pass over
// the function eliminating them. While we are at it, remember where we see
// calls to llvm.gcroot.
std::vector<CallInst*> GCRoots;
std::vector<CallInst*> NormalCalls;
bool MadeChange = false;
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;)
if (CallInst *CI = dyn_cast<CallInst>(II++)) {
if (!CI->getCalledFunction() ||
!CI->getCalledFunction()->isIntrinsic())
NormalCalls.push_back(CI); // Remember all normal function calls.
if (Function *F = CI->getCalledFunction())
if (F == GCRootInt)
GCRoots.push_back(CI);
else if (F == GCReadInt || F == GCWriteInt) {
if (F == GCWriteInt) {
// Change a llvm.gcwrite call to call llvm_gc_write instead.
CI->setOperand(0, GCWrite);
// Insert casts of the operands as needed.
Coerce(CI, 1, VoidPtr);
Coerce(CI, 2, VoidPtr);
Coerce(CI, 3, VoidPtrPtr);
} else {
Coerce(CI, 1, VoidPtr);
Coerce(CI, 2, VoidPtrPtr);
if (CI->getType() == VoidPtr) {
CI->setOperand(0, GCRead);
} else {
// Create a whole new call to replace the old one.
// It sure would be nice to pass op_begin()+1,
// op_begin()+2 but it runs into trouble with
// CallInst::init's &*iterator, which requires a
// conversion from Use* to Value*. The conversion
// from Use to Value * is not useful because the
// memory for Value * won't be contiguous.
Value* Args[] = {
CI->getOperand(1),
CI->getOperand(2)
};
CallInst *NC = new CallInst(GCRead, Args, Args + 2,
CI->getName(), CI);
// These functions only deal with ptr type results so BitCast
// is the correct kind of cast (no-op cast).
Value *NV = new BitCastInst(NC, CI->getType(), "", CI);
CI->replaceAllUsesWith(NV);
BB->getInstList().erase(CI);
CI = NC;
}
}
MadeChange = true;
}
}
// If there are no GC roots in this function, then there is no need to create
// a GC list record for it.
if (GCRoots.empty()) return MadeChange;
// Okay, there are GC roots in this function. On entry to the function, add a
// record to the llvm_gc_root_chain, and remove it on exit.
// Create the alloca, and zero it out.
const StructType *RootListTy = getRootRecordType(GCRoots.size());
AllocaInst *AI = new AllocaInst(RootListTy, 0, "gcroots", F.begin()->begin());
// Insert the memset call after all of the allocas in the function.
BasicBlock::iterator IP = AI;
while (isa<AllocaInst>(IP)) ++IP;
Constant *Zero = ConstantInt::get(Type::Int32Ty, 0);
Constant *One = ConstantInt::get(Type::Int32Ty, 1);
Value *Idx[2] = { Zero, Zero };
// Get a pointer to the prev pointer.
Value *PrevPtrPtr = new GetElementPtrInst(AI, Idx, Idx + 2,
"prevptrptr", IP);
// Load the previous pointer.
Value *PrevPtr = new LoadInst(RootChain, "prevptr", IP);
// Store the previous pointer into the prevptrptr
new StoreInst(PrevPtr, PrevPtrPtr, IP);
// Set the number of elements in this record.
Idx[1] = One;
Value *NumEltsPtr = new GetElementPtrInst(AI, Idx, Idx + 2,
"numeltsptr", IP);
new StoreInst(ConstantInt::get(Type::Int32Ty, GCRoots.size()), NumEltsPtr,IP);
Value* Par[4];
Par[0] = Zero;
Par[1] = ConstantInt::get(Type::Int32Ty, 2);
const PointerType *PtrLocTy =
cast<PointerType>(GCRootInt->getFunctionType()->getParamType(0));
Constant *Null = ConstantPointerNull::get(PtrLocTy);
// Initialize all of the gcroot records now.
for (unsigned i = 0, e = GCRoots.size(); i != e; ++i) {
// Initialize the meta-data pointer.
Par[2] = ConstantInt::get(Type::Int32Ty, i);
Par[3] = One;
Value *MetaDataPtr = new GetElementPtrInst(AI, Par, Par + 4,
"MetaDataPtr", IP);
assert(isa<Constant>(GCRoots[i]->getOperand(2)) && "Must be a constant");
new StoreInst(GCRoots[i]->getOperand(2), MetaDataPtr, IP);
// Initialize the root pointer to null on entry to the function.
Par[3] = Zero;
Value *RootPtrPtr = new GetElementPtrInst(AI, Par, Par + 4,
"RootEntPtr", IP);
new StoreInst(Null, RootPtrPtr, IP);
// Each occurrance of the llvm.gcroot intrinsic now turns into an
// initialization of the slot with the address.
new StoreInst(GCRoots[i]->getOperand(1), RootPtrPtr, GCRoots[i]);
}
// Now that the record is all initialized, store the pointer into the global
// pointer.
Value *C = new BitCastInst(AI, PointerType::getUnqual(MainRootRecordType), "", IP);
new StoreInst(C, RootChain, IP);
// Eliminate all the gcroot records now.
for (unsigned i = 0, e = GCRoots.size(); i != e; ++i)
GCRoots[i]->getParent()->getInstList().erase(GCRoots[i]);
// On exit from the function we have to remove the entry from the GC root
// chain. Doing this is straight-forward for return and unwind instructions:
// just insert the appropriate copy.
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
if (isa<UnwindInst>(BB->getTerminator()) ||
isa<ReturnInst>(BB->getTerminator())) {
// We could reuse the PrevPtr loaded on entry to the function, but this
// would make the value live for the whole function, which is probably a
// bad idea. Just reload the value out of our stack entry.
PrevPtr = new LoadInst(PrevPtrPtr, "prevptr", BB->getTerminator());
new StoreInst(PrevPtr, RootChain, BB->getTerminator());
}
// If an exception is thrown from a callee we have to make sure to
// unconditionally take the record off the stack. For this reason, we turn
// all call instructions into invoke whose cleanup pops the entry off the
// stack. We only insert one cleanup block, which is shared by all invokes.
if (!NormalCalls.empty()) {
// Create the shared cleanup block.
BasicBlock *Cleanup = new BasicBlock("gc_cleanup", &F);
UnwindInst *UI = new UnwindInst(Cleanup);
PrevPtr = new LoadInst(PrevPtrPtr, "prevptr", UI);
new StoreInst(PrevPtr, RootChain, UI);
// Loop over all of the function calls, turning them into invokes.
while (!NormalCalls.empty()) {
CallInst *CI = NormalCalls.back();
BasicBlock *CBB = CI->getParent();
NormalCalls.pop_back();
// Split the basic block containing the function call.
BasicBlock *NewBB = CBB->splitBasicBlock(CI, CBB->getName()+".cont");
// Remove the unconditional branch inserted at the end of the CBB.
CBB->getInstList().pop_back();
NewBB->getInstList().remove(CI);
// Create a new invoke instruction.
std::vector<Value*> Args(CI->op_begin()+1, CI->op_end());
Value *II = new InvokeInst(CI->getCalledValue(), NewBB, Cleanup,
Args.begin(), Args.end(), CI->getName(), CBB);
cast<InvokeInst>(II)->setCallingConv(CI->getCallingConv());
cast<InvokeInst>(II)->setParamAttrs(CI->getParamAttrs());
CI->replaceAllUsesWith(II);
delete CI;
}
}
return true;
}

30
runtime/GC/SemiSpace/semispace.c
View File

@ -97,24 +97,26 @@ void llvm_gc_write(void *V, void *ObjPtr, void **FieldPtr) { *FieldPtr = V; }
* FIXME: This should be in a code-generator specific library, but for now this
* will work for all code generators.
*/
typedef struct GCRoot {
void **RootPtr;
void *Meta;
} GCRoot;
struct FrameMap {
int32_t NumRoots; // Number of roots in stack frame.
int32_t NumMeta; // Number of metadata descriptors. May be < NumRoots.
void *Meta[]; // May be absent for roots without metadata.
};
typedef struct GCRoots {
struct GCRoots *Next;
unsigned NumRoots;
GCRoot RootRecords[];
} GCRoots;
GCRoots *llvm_gc_root_chain;
struct StackEntry {
ShadowStackEntry *Next; // Caller's stack entry.
const FrameMap *Map; // Pointer to constant FrameMap.
void *Roots[]; // Stack roots (in-place array).
};
StackEntry *llvm_gc_root_chain;
void llvm_cg_walk_gcroots(void (*FP)(void **Root, void *Meta)) {
GCRoots *R = llvm_gc_root_chain;
for (; R; R = R->Next) {
for (StackEntry *R; R; R = R->Next) {
unsigned i, e;
for (i = 0, e = R->NumRoots; i != e; ++i)
FP(R->RootRecords[i].RootPtr, R->RootRecords[i].Meta);
for (i = 0, e = R->NumMeta; i != e; ++i)
FP(&R->Roots[i], R->Map->Meta[i]);
for (e = R->NumRoots; i != e; ++i)
FP(&R->Roots[i], NULL);
}
}
/* END FIXME! */

17
test/CodeGen/Generic/GC/redundant_init.ll Normal file
View File

@ -0,0 +1,17 @@
; RUN: llvm-as < %s | llc -march=x86 | \
; RUN: ignore grep {movl..0} | count 0
%struct.obj = type { i8*, %struct.obj* }
declare void @g() gc "shadow-stack"
define void @f(i8* %o) gc "shadow-stack" {
entry:
%root = alloca i8*
call void @llvm.gcroot(i8** %root, i8* null)
store i8* %o, i8** %root
call void @g()
ret void
}
declare void @llvm.gcroot(i8**, i8*)