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llvm-mirror/lib/Transforms/IPO/LowerSetJmp.cpp
Benjamin Kramer c6b59b889b Eliminate some temporaries. 
llvm-svn: 85896
2009-11-03 12:52:50 +00:00

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//===- LowerSetJmp.cpp - Code pertaining to lowering set/long jumps -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the lowering of setjmp and longjmp to use the
// LLVM invoke and unwind instructions as necessary.
//
// Lowering of longjmp is fairly trivial. We replace the call with a
// call to the LLVM library function "__llvm_sjljeh_throw_longjmp()".
// This unwinds the stack for us calling all of the destructors for
// objects allocated on the stack.
//
// At a setjmp call, the basic block is split and the setjmp removed.
// The calls in a function that have a setjmp are converted to invoke
// where the except part checks to see if it's a longjmp exception and,
// if so, if it's handled in the function. If it is, then it gets the
// value returned by the longjmp and goes to where the basic block was
// split. Invoke instructions are handled in a similar fashion with the
// original except block being executed if it isn't a longjmp except
// that is handled by that function.
//
//===----------------------------------------------------------------------===//
//===----------------------------------------------------------------------===//
// FIXME: This pass doesn't deal with PHI statements just yet. That is,
// we expect this to occur before SSAification is done. This would seem
// to make sense, but in general, it might be a good idea to make this
// pass invokable via the "opt" command at will.
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "lowersetjmp"
#include "llvm/Transforms/IPO.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Intrinsics.h"
#include "llvm/LLVMContext.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
#include <map>
using namespace llvm;
STATISTIC(LongJmpsTransformed, "Number of longjmps transformed");
STATISTIC(SetJmpsTransformed , "Number of setjmps transformed");
STATISTIC(CallsTransformed , "Number of calls invokified");
STATISTIC(InvokesTransformed , "Number of invokes modified");
namespace {
//===--------------------------------------------------------------------===//
// LowerSetJmp pass implementation.
class LowerSetJmp : public ModulePass, public InstVisitor<LowerSetJmp> {
// LLVM library functions...
Constant *InitSJMap; // __llvm_sjljeh_init_setjmpmap
Constant *DestroySJMap; // __llvm_sjljeh_destroy_setjmpmap
Constant *AddSJToMap; // __llvm_sjljeh_add_setjmp_to_map
Constant *ThrowLongJmp; // __llvm_sjljeh_throw_longjmp
Constant *TryCatchLJ; // __llvm_sjljeh_try_catching_longjmp_exception
Constant *IsLJException; // __llvm_sjljeh_is_longjmp_exception
Constant *GetLJValue; // __llvm_sjljeh_get_longjmp_value
typedef std::pair<SwitchInst*, CallInst*> SwitchValuePair;
// Keep track of those basic blocks reachable via a depth-first search of
// the CFG from a setjmp call. We only need to transform those "call" and
// "invoke" instructions that are reachable from the setjmp call site.
std::set<BasicBlock*> DFSBlocks;
// The setjmp map is going to hold information about which setjmps
// were called (each setjmp gets its own number) and with which
// buffer it was called.
std::map<Function*, AllocaInst*> SJMap;
// The rethrow basic block map holds the basic block to branch to if
// the exception isn't handled in the current function and needs to
// be rethrown.
std::map<const Function*, BasicBlock*> RethrowBBMap;
// The preliminary basic block map holds a basic block that grabs the
// exception and determines if it's handled by the current function.
std::map<const Function*, BasicBlock*> PrelimBBMap;
// The switch/value map holds a switch inst/call inst pair. The
// switch inst controls which handler (if any) gets called and the
// value is the value returned to that handler by the call to
// __llvm_sjljeh_get_longjmp_value.
std::map<const Function*, SwitchValuePair> SwitchValMap;
// A map of which setjmps we've seen so far in a function.
std::map<const Function*, unsigned> SetJmpIDMap;
AllocaInst* GetSetJmpMap(Function* Func);
BasicBlock* GetRethrowBB(Function* Func);
SwitchValuePair GetSJSwitch(Function* Func, BasicBlock* Rethrow);
void TransformLongJmpCall(CallInst* Inst);
void TransformSetJmpCall(CallInst* Inst);
bool IsTransformableFunction(StringRef Name);
public:
static char ID; // Pass identification, replacement for typeid
LowerSetJmp() : ModulePass(&ID) {}
void visitCallInst(CallInst& CI);
void visitInvokeInst(InvokeInst& II);
void visitReturnInst(ReturnInst& RI);
void visitUnwindInst(UnwindInst& UI);
bool runOnModule(Module& M);
bool doInitialization(Module& M);
};
} // end anonymous namespace
char LowerSetJmp::ID = 0;
static RegisterPass<LowerSetJmp> X("lowersetjmp", "Lower Set Jump");
// run - Run the transformation on the program. We grab the function
// prototypes for longjmp and setjmp. If they are used in the program,
// then we can go directly to the places they're at and transform them.
bool LowerSetJmp::runOnModule(Module& M) {
bool Changed = false;
// These are what the functions are called.
Function* SetJmp = M.getFunction("llvm.setjmp");
Function* LongJmp = M.getFunction("llvm.longjmp");
// This program doesn't have longjmp and setjmp calls.
if ((!LongJmp || LongJmp->use_empty()) &&
(!SetJmp || SetJmp->use_empty())) return false;
// Initialize some values and functions we'll need to transform the
// setjmp/longjmp functions.
doInitialization(M);
if (SetJmp) {
for (Value::use_iterator B = SetJmp->use_begin(), E = SetJmp->use_end();
B != E; ++B) {
BasicBlock* BB = cast<Instruction>(*B)->getParent();
for (df_ext_iterator<BasicBlock*> I = df_ext_begin(BB, DFSBlocks),
E = df_ext_end(BB, DFSBlocks); I != E; ++I)
/* empty */;
}
while (!SetJmp->use_empty()) {
assert(isa<CallInst>(SetJmp->use_back()) &&
"User of setjmp intrinsic not a call?");
TransformSetJmpCall(cast<CallInst>(SetJmp->use_back()));
Changed = true;
}
}
if (LongJmp)
while (!LongJmp->use_empty()) {
assert(isa<CallInst>(LongJmp->use_back()) &&
"User of longjmp intrinsic not a call?");
TransformLongJmpCall(cast<CallInst>(LongJmp->use_back()));
Changed = true;
}
// Now go through the affected functions and convert calls and invokes
// to new invokes...
for (std::map<Function*, AllocaInst*>::iterator
B = SJMap.begin(), E = SJMap.end(); B != E; ++B) {
Function* F = B->first;
for (Function::iterator BB = F->begin(), BE = F->end(); BB != BE; ++BB)
for (BasicBlock::iterator IB = BB->begin(), IE = BB->end(); IB != IE; ) {
visit(*IB++);
if (IB != BB->end() && IB->getParent() != BB)
break; // The next instruction got moved to a different block!
}
}
DFSBlocks.clear();
SJMap.clear();
RethrowBBMap.clear();
PrelimBBMap.clear();
SwitchValMap.clear();
SetJmpIDMap.clear();
return Changed;
}
// doInitialization - For the lower long/setjmp pass, this ensures that a
// module contains a declaration for the intrisic functions we are going
// to call to convert longjmp and setjmp calls.
//
// This function is always successful, unless it isn't.
bool LowerSetJmp::doInitialization(Module& M)
{
const Type *SBPTy = Type::getInt8PtrTy(M.getContext());
const Type *SBPPTy = PointerType::getUnqual(SBPTy);
// N.B. See llvm/runtime/GCCLibraries/libexception/SJLJ-Exception.h for
// a description of the following library functions.
// void __llvm_sjljeh_init_setjmpmap(void**)
InitSJMap = M.getOrInsertFunction("__llvm_sjljeh_init_setjmpmap",
Type::getVoidTy(M.getContext()),
SBPPTy, (Type *)0);
// void __llvm_sjljeh_destroy_setjmpmap(void**)
DestroySJMap = M.getOrInsertFunction("__llvm_sjljeh_destroy_setjmpmap",
Type::getVoidTy(M.getContext()),
SBPPTy, (Type *)0);
// void __llvm_sjljeh_add_setjmp_to_map(void**, void*, unsigned)
AddSJToMap = M.getOrInsertFunction("__llvm_sjljeh_add_setjmp_to_map",
Type::getVoidTy(M.getContext()),
SBPPTy, SBPTy,
Type::getInt32Ty(M.getContext()),
(Type *)0);
// void __llvm_sjljeh_throw_longjmp(int*, int)
ThrowLongJmp = M.getOrInsertFunction("__llvm_sjljeh_throw_longjmp",
Type::getVoidTy(M.getContext()), SBPTy,
Type::getInt32Ty(M.getContext()),
(Type *)0);
// unsigned __llvm_sjljeh_try_catching_longjmp_exception(void **)
TryCatchLJ =
M.getOrInsertFunction("__llvm_sjljeh_try_catching_longjmp_exception",
Type::getInt32Ty(M.getContext()), SBPPTy, (Type *)0);
// bool __llvm_sjljeh_is_longjmp_exception()
IsLJException = M.getOrInsertFunction("__llvm_sjljeh_is_longjmp_exception",
Type::getInt1Ty(M.getContext()),
(Type *)0);
// int __llvm_sjljeh_get_longjmp_value()
GetLJValue = M.getOrInsertFunction("__llvm_sjljeh_get_longjmp_value",
Type::getInt32Ty(M.getContext()),
(Type *)0);
return true;
}
// IsTransformableFunction - Return true if the function name isn't one
// of the ones we don't want transformed. Currently, don't transform any
// "llvm.{setjmp,longjmp}" functions and none of the setjmp/longjmp error
// handling functions (beginning with __llvm_sjljeh_...they don't throw
// exceptions).
bool LowerSetJmp::IsTransformableFunction(StringRef Name) {
return !Name.startswith("__llvm_sjljeh_");
}
// TransformLongJmpCall - Transform a longjmp call into a call to the
// internal __llvm_sjljeh_throw_longjmp function. It then takes care of
// throwing the exception for us.
void LowerSetJmp::TransformLongJmpCall(CallInst* Inst)
{
const Type* SBPTy = Type::getInt8PtrTy(Inst->getContext());
// Create the call to "__llvm_sjljeh_throw_longjmp". This takes the
// same parameters as "longjmp", except that the buffer is cast to a
// char*. It returns "void", so it doesn't need to replace any of
// Inst's uses and doesn't get a name.
CastInst* CI =
new BitCastInst(Inst->getOperand(1), SBPTy, "LJBuf", Inst);
Value *Args[] = { CI, Inst->getOperand(2) };
CallInst::Create(ThrowLongJmp, Args, Args + 2, "", Inst);
SwitchValuePair& SVP = SwitchValMap[Inst->getParent()->getParent()];
// If the function has a setjmp call in it (they are transformed first)
// we should branch to the basic block that determines if this longjmp
// is applicable here. Otherwise, issue an unwind.
if (SVP.first)
BranchInst::Create(SVP.first->getParent(), Inst);
else
new UnwindInst(Inst->getContext(), Inst);
// Remove all insts after the branch/unwind inst. Go from back to front to
// avoid replaceAllUsesWith if possible.
BasicBlock *BB = Inst->getParent();
Instruction *Removed;
do {
Removed = &BB->back();
// If the removed instructions have any users, replace them now.
if (!Removed->use_empty())
Removed->replaceAllUsesWith(UndefValue::get(Removed->getType()));
Removed->eraseFromParent();
} while (Removed != Inst);
++LongJmpsTransformed;
}
// GetSetJmpMap - Retrieve (create and initialize, if necessary) the
// setjmp map. This map is going to hold information about which setjmps
// were called (each setjmp gets its own number) and with which buffer it
// was called. There can be only one!
AllocaInst* LowerSetJmp::GetSetJmpMap(Function* Func)
{
if (SJMap[Func]) return SJMap[Func];
// Insert the setjmp map initialization before the first instruction in
// the function.
Instruction* Inst = Func->getEntryBlock().begin();
assert(Inst && "Couldn't find even ONE instruction in entry block!");
// Fill in the alloca and call to initialize the SJ map.
const Type *SBPTy =
Type::getInt8PtrTy(Func->getContext());
AllocaInst* Map = new AllocaInst(SBPTy, 0, "SJMap", Inst);
CallInst::Create(InitSJMap, Map, "", Inst);
return SJMap[Func] = Map;
}
// GetRethrowBB - Only one rethrow basic block is needed per function.
// If this is a longjmp exception but not handled in this block, this BB
// performs the rethrow.
BasicBlock* LowerSetJmp::GetRethrowBB(Function* Func)
{
if (RethrowBBMap[Func]) return RethrowBBMap[Func];
// The basic block we're going to jump to if we need to rethrow the
// exception.
BasicBlock* Rethrow =
BasicBlock::Create(Func->getContext(), "RethrowExcept", Func);
// Fill in the "Rethrow" BB with a call to rethrow the exception. This
// is the last instruction in the BB since at this point the runtime
// should exit this function and go to the next function.
new UnwindInst(Func->getContext(), Rethrow);
return RethrowBBMap[Func] = Rethrow;
}
// GetSJSwitch - Return the switch statement that controls which handler
// (if any) gets called and the value returned to that handler.
LowerSetJmp::SwitchValuePair LowerSetJmp::GetSJSwitch(Function* Func,
BasicBlock* Rethrow)
{
if (SwitchValMap[Func].first) return SwitchValMap[Func];
BasicBlock* LongJmpPre =
BasicBlock::Create(Func->getContext(), "LongJmpBlkPre", Func);
// Keep track of the preliminary basic block for some of the other
// transformations.
PrelimBBMap[Func] = LongJmpPre;
// Grab the exception.
CallInst* Cond = CallInst::Create(IsLJException, "IsLJExcept", LongJmpPre);
// The "decision basic block" gets the number associated with the
// setjmp call returning to switch on and the value returned by
// longjmp.
BasicBlock* DecisionBB =
BasicBlock::Create(Func->getContext(), "LJDecisionBB", Func);
BranchInst::Create(DecisionBB, Rethrow, Cond, LongJmpPre);
// Fill in the "decision" basic block.
CallInst* LJVal = CallInst::Create(GetLJValue, "LJVal", DecisionBB);
CallInst* SJNum = CallInst::Create(TryCatchLJ, GetSetJmpMap(Func), "SJNum",
DecisionBB);
SwitchInst* SI = SwitchInst::Create(SJNum, Rethrow, 0, DecisionBB);
return SwitchValMap[Func] = SwitchValuePair(SI, LJVal);
}
// TransformSetJmpCall - The setjmp call is a bit trickier to transform.
// We're going to convert all setjmp calls to nops. Then all "call" and
// "invoke" instructions in the function are converted to "invoke" where
// the "except" branch is used when returning from a longjmp call.
void LowerSetJmp::TransformSetJmpCall(CallInst* Inst)
{
BasicBlock* ABlock = Inst->getParent();
Function* Func = ABlock->getParent();
// Add this setjmp to the setjmp map.
const Type* SBPTy =
Type::getInt8PtrTy(Inst->getContext());
CastInst* BufPtr =
new BitCastInst(Inst->getOperand(1), SBPTy, "SBJmpBuf", Inst);
Value *Args[] = {
GetSetJmpMap(Func), BufPtr,
ConstantInt::get(Type::getInt32Ty(Inst->getContext()), SetJmpIDMap[Func]++)
};
CallInst::Create(AddSJToMap, Args, Args + 3, "", Inst);
// We are guaranteed that there are no values live across basic blocks
// (because we are "not in SSA form" yet), but there can still be values live
// in basic blocks. Because of this, splitting the setjmp block can cause
// values above the setjmp to not dominate uses which are after the setjmp
// call. For all of these occasions, we must spill the value to the stack.
//
std::set<Instruction*> InstrsAfterCall;
// The call is probably very close to the end of the basic block, for the
// common usage pattern of: 'if (setjmp(...))', so keep track of the
// instructions after the call.
for (BasicBlock::iterator I = ++BasicBlock::iterator(Inst), E = ABlock->end();
I != E; ++I)
InstrsAfterCall.insert(I);
for (BasicBlock::iterator II = ABlock->begin();
II != BasicBlock::iterator(Inst); ++II)
// Loop over all of the uses of instruction. If any of them are after the
// call, "spill" the value to the stack.
for (Value::use_iterator UI = II->use_begin(), E = II->use_end();
UI != E; ++UI)
if (cast<Instruction>(*UI)->getParent() != ABlock ||
InstrsAfterCall.count(cast<Instruction>(*UI))) {
DemoteRegToStack(*II);
break;
}
InstrsAfterCall.clear();
// Change the setjmp call into a branch statement. We'll remove the
// setjmp call in a little bit. No worries.
BasicBlock* SetJmpContBlock = ABlock->splitBasicBlock(Inst);
assert(SetJmpContBlock && "Couldn't split setjmp BB!!");
SetJmpContBlock->setName(ABlock->getName()+"SetJmpCont");
// Add the SetJmpContBlock to the set of blocks reachable from a setjmp.
DFSBlocks.insert(SetJmpContBlock);
// This PHI node will be in the new block created from the
// splitBasicBlock call.
PHINode* PHI = PHINode::Create(Type::getInt32Ty(Inst->getContext()),
"SetJmpReturn", Inst);
// Coming from a call to setjmp, the return is 0.
PHI->addIncoming(Constant::getNullValue(Type::getInt32Ty(Inst->getContext())),
ABlock);
// Add the case for this setjmp's number...
SwitchValuePair SVP = GetSJSwitch(Func, GetRethrowBB(Func));
SVP.first->addCase(ConstantInt::get(Type::getInt32Ty(Inst->getContext()),
SetJmpIDMap[Func] - 1),
SetJmpContBlock);
// Value coming from the handling of the exception.
PHI->addIncoming(SVP.second, SVP.second->getParent());
// Replace all uses of this instruction with the PHI node created by
// the eradication of setjmp.
Inst->replaceAllUsesWith(PHI);
Inst->eraseFromParent();
++SetJmpsTransformed;
}
// visitCallInst - This converts all LLVM call instructions into invoke
// instructions. The except part of the invoke goes to the "LongJmpBlkPre"
// that grabs the exception and proceeds to determine if it's a longjmp
// exception or not.
void LowerSetJmp::visitCallInst(CallInst& CI)
{
if (CI.getCalledFunction())
if (!IsTransformableFunction(CI.getCalledFunction()->getName()) ||
CI.getCalledFunction()->isIntrinsic()) return;
BasicBlock* OldBB = CI.getParent();
// If not reachable from a setjmp call, don't transform.
if (!DFSBlocks.count(OldBB)) return;
BasicBlock* NewBB = OldBB->splitBasicBlock(CI);
assert(NewBB && "Couldn't split BB of \"call\" instruction!!");
DFSBlocks.insert(NewBB);
NewBB->setName("Call2Invoke");
Function* Func = OldBB->getParent();
// Construct the new "invoke" instruction.
TerminatorInst* Term = OldBB->getTerminator();
std::vector<Value*> Params(CI.op_begin() + 1, CI.op_end());
InvokeInst* II =
InvokeInst::Create(CI.getCalledValue(), NewBB, PrelimBBMap[Func],
Params.begin(), Params.end(), CI.getName(), Term);
II->setCallingConv(CI.getCallingConv());
II->setAttributes(CI.getAttributes());
// Replace the old call inst with the invoke inst and remove the call.
CI.replaceAllUsesWith(II);
CI.eraseFromParent();
// The old terminator is useless now that we have the invoke inst.
Term->eraseFromParent();
++CallsTransformed;
}
// visitInvokeInst - Converting the "invoke" instruction is fairly
// straight-forward. The old exception part is replaced by a query asking
// if this is a longjmp exception. If it is, then it goes to the longjmp
// exception blocks. Otherwise, control is passed the old exception.
void LowerSetJmp::visitInvokeInst(InvokeInst& II)
{
if (II.getCalledFunction())
if (!IsTransformableFunction(II.getCalledFunction()->getName()) ||
II.getCalledFunction()->isIntrinsic()) return;
BasicBlock* BB = II.getParent();
// If not reachable from a setjmp call, don't transform.
if (!DFSBlocks.count(BB)) return;
BasicBlock* ExceptBB = II.getUnwindDest();
Function* Func = BB->getParent();
BasicBlock* NewExceptBB = BasicBlock::Create(II.getContext(),
"InvokeExcept", Func);
// If this is a longjmp exception, then branch to the preliminary BB of
// the longjmp exception handling. Otherwise, go to the old exception.
CallInst* IsLJExcept = CallInst::Create(IsLJException, "IsLJExcept",
NewExceptBB);
BranchInst::Create(PrelimBBMap[Func], ExceptBB, IsLJExcept, NewExceptBB);
II.setUnwindDest(NewExceptBB);
++InvokesTransformed;
}
// visitReturnInst - We want to destroy the setjmp map upon exit from the
// function.
void LowerSetJmp::visitReturnInst(ReturnInst &RI) {
Function* Func = RI.getParent()->getParent();
CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &RI);
}
// visitUnwindInst - We want to destroy the setjmp map upon exit from the
// function.
void LowerSetJmp::visitUnwindInst(UnwindInst &UI) {
Function* Func = UI.getParent()->getParent();
CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &UI);
}
ModulePass *llvm::createLowerSetJmpPass() {
return new LowerSetJmp();
}
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