llvm-6502/lib/Transforms/Scalar/LowerGC.cpp

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//===-- LowerGC.cpp - Provide GC support for targets that don't -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and 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::get(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::get(Type::Int8Ty);
PointerType *VoidPtrPtr = PointerType::get(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::get(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::get(Type::Int8Ty);
PointerType *VoidPtrPtr = PointerType::get(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()->getIntrinsicID())
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::get(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);
CI->replaceAllUsesWith(II);
delete CI;
}
}
return true;
}