Rebased PNaCl localmods in LLVM to 223109

lib/Transforms/NaCl/PNaClSjLjEH.cpp

+//===- PNaClSjLjEH.cpp - Lower C++ exception handling to use setjmp()------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// The PNaClSjLjEH pass is part of an implementation of C++ exception
+// handling for PNaCl that uses setjmp() and longjmp() to handle C++
+// exceptions.  The pass lowers LLVM "invoke" instructions to use
+// setjmp().
+//
+// For example, consider the following C++ code fragment:
+//
+//   int catcher_func() {
+//     try {
+//       int result = external_func();
+//       return result + 100;
+//     } catch (MyException &exc) {
+//       return exc.value + 200;
+//     }
+//   }
+//
+// PNaClSjLjEH converts the IR for that function to the following
+// pseudo-code:
+//
+//   struct LandingPadResult {
+//     void *exception_obj;  // For passing to __cxa_begin_catch()
+//     int matched_clause_id;  // See ExceptionInfoWriter.cpp
+//   };
+//
+//   struct ExceptionFrame {
+//     union {
+//       jmp_buf jmpbuf;  // Context for jumping to landingpad block
+//       struct LandingPadResult result;  // Data returned to landingpad block
+//     };
+//     struct ExceptionFrame *next;  // Next frame in linked list
+//     int clause_list_id;  // Reference to landingpad's exception info
+//   };
+//
+//   // Thread-local exception state
+//   __thread struct ExceptionFrame *__pnacl_eh_stack;
+//
+//   int catcher_func() {
+//     struct ExceptionFrame frame;
+//     frame.next = __pnacl_eh_stack;
+//     frame.clause_list_id = 123;
+//     __pnacl_eh_stack = &frame;  // Add frame to stack
+//     int result;
+//     if (!catcher_func_setjmp_caller(external_func, &frame.jmpbuf, &result)) {
+//       __pnacl_eh_stack = frame.next;  // Remove frame from stack
+//       return result + 100;
+//     } else {
+//       // Handle exception.  This is a simplification.  Real code would
+//       // call __cxa_begin_catch() to extract the thrown object.
+//       MyException &exc = *(MyException *) frame.result.exception_obj;
+//       return exc.value + 200;
+//     }
+//   }
+//
+//   // Helper function
+//   static int catcher_func_setjmp_caller(int (*func)(void), jmp_buf jmpbuf,
+//                                         int *result) {
+//     if (!setjmp(jmpbuf)) {
+//       *result = func();
+//       return 0;
+//     }
+//     return 1;
+//   }
+//
+// We use a helper function so that setjmp() is not called directly
+// from catcher_func(), due to a quirk of how setjmp() and longjmp()
+// are specified in C.
+//
+// func() might modify variables (allocas) that are local to
+// catcher_func() (if the variables' addresses are taken).  The C
+// standard says that these variables' values would become undefined
+// after longjmp() returned if setjmp() were called from
+// catcher_func().  Specifically, LLVM's GVN pass can optimize away
+// stores to allocas between setjmp() and longjmp() (see
+// pnacl-sjlj-eh-bug.ll for an example).  But this only applies to
+// allocas inside the caller of setjmp(), not to allocas inside the
+// caller of the caller of setjmp(), so doing the setjmp() call inside
+// a helper function that catcher_func() calls avoids the problem.
+//
+// The pass makes the following changes to IR:
+//
+//  * Convert "invoke" and "landingpad" instructions.
+//  * Convert "resume" instructions into __pnacl_eh_resume() calls.
+//  * Replace each call to llvm.eh.typeid.for() with an integer
+//    constant representing the exception type.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/NaCl.h"
+#include "ExceptionInfoWriter.h"
+
+using namespace llvm;
+
+namespace {
+  // This is a ModulePass so that it can introduce new global variables.
+  class PNaClSjLjEH : public ModulePass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    PNaClSjLjEH() : ModulePass(ID) {
+      initializePNaClSjLjEHPass(*PassRegistry::getPassRegistry());
+    }
+
+    virtual bool runOnModule(Module &M);
+  };
+
+  class FuncRewriter {
+    Type *ExceptionFrameTy;
+    ExceptionInfoWriter *ExcInfoWriter;
+    Function *Func;
+
+    // FrameInitialized indicates whether the following variables have
+    // been initialized.
+    bool FrameInitialized;
+    Function *SetjmpIntrinsic;  // setjmp() intrinsic function
+    Instruction *EHStackTlsVar;  // Bitcast of thread-local __pnacl_eh_stack var
+    Instruction *Frame;  // Frame allocated for this function
+    Instruction *FrameJmpBuf;  // Frame's jmp_buf field
+    Instruction *FrameNextPtr;  // Frame's next field
+    Instruction *FrameExcInfo;  // Frame's clause_list_id field
+
+    Function *EHResumeFunc;  // __pnacl_eh_resume() function
+
+    // Initialize values that are shared across all "invoke"
+    // instructions within the function.
+    void initializeFrame();
+
+  public:
+    FuncRewriter(Type *ExceptionFrameTy, ExceptionInfoWriter *ExcInfoWriter,
+                 Function *Func):
+        ExceptionFrameTy(ExceptionFrameTy),
+        ExcInfoWriter(ExcInfoWriter),
+        Func(Func),
+        FrameInitialized(false),
+        SetjmpIntrinsic(NULL), EHStackTlsVar(NULL),
+        Frame(NULL), FrameJmpBuf(NULL), FrameNextPtr(NULL), FrameExcInfo(NULL),
+        EHResumeFunc(NULL) {}
+
+    Value *createSetjmpWrappedCall(InvokeInst *Invoke);
+    void expandInvokeInst(InvokeInst *Invoke);
+    void expandResumeInst(ResumeInst *Resume);
+    void expandFunc();
+  };
+}
+
+char PNaClSjLjEH::ID = 0;
+INITIALIZE_PASS(PNaClSjLjEH, "pnacl-sjlj-eh",
+                "Lower C++ exception handling to use setjmp()",
+                false, false)
+
+static const int kPNaClJmpBufSize = 1024;
+static const int kPNaClJmpBufAlign = 8;
+
+void FuncRewriter::initializeFrame() {
+  if (FrameInitialized)
+    return;
+  FrameInitialized = true;
+  Module *M = Func->getParent();
+
+  SetjmpIntrinsic = Intrinsic::getDeclaration(M, Intrinsic::nacl_setjmp);
+
+  Value *EHStackTlsVarUncast = M->getGlobalVariable("__pnacl_eh_stack");
+  if (!EHStackTlsVarUncast)
+    report_fatal_error("__pnacl_eh_stack not defined");
+  EHStackTlsVar = new BitCastInst(
+      EHStackTlsVarUncast, ExceptionFrameTy->getPointerTo()->getPointerTo(),
+      "pnacl_eh_stack");
+  Func->getEntryBlock().getInstList().push_front(EHStackTlsVar);
+
+  // Allocate the new exception frame.  This is reused across all
+  // invoke instructions in the function.
+  Type *I32 = Type::getInt32Ty(M->getContext());
+  Frame = new AllocaInst(ExceptionFrameTy, ConstantInt::get(I32, 1),
+                         kPNaClJmpBufAlign, "invoke_frame");
+  Func->getEntryBlock().getInstList().push_front(Frame);
+
+  // Calculate addresses of fields in the exception frame.
+  Value *JmpBufIndexes[] = { ConstantInt::get(I32, 0),
+                             ConstantInt::get(I32, 0),
+                             ConstantInt::get(I32, 0) };
+  FrameJmpBuf = GetElementPtrInst::Create(Frame, JmpBufIndexes,
+                                          "invoke_jmp_buf");
+  FrameJmpBuf->insertAfter(Frame);
+
+  Value *NextPtrIndexes[] = { ConstantInt::get(I32, 0),
+                              ConstantInt::get(I32, 1) };
+  FrameNextPtr = GetElementPtrInst::Create(Frame, NextPtrIndexes,
+                                           "invoke_next");
+  FrameNextPtr->insertAfter(Frame);
+
+  Value *ExcInfoIndexes[] = { ConstantInt::get(I32, 0),
+                              ConstantInt::get(I32, 2) };
+  FrameExcInfo = GetElementPtrInst::Create(Frame, ExcInfoIndexes,
+                                           "exc_info_ptr");
+  FrameExcInfo->insertAfter(Frame);
+}
+
+// Creates the helper function that will do the setjmp() call and
+// function call for implementing Invoke.  Creates the call to the
+// helper function.  Returns a Value which is zero on the normal
+// execution path and non-zero if the landingpad block should be
+// entered.
+Value *FuncRewriter::createSetjmpWrappedCall(InvokeInst *Invoke) {
+  Type *I32 = Type::getInt32Ty(Func->getContext());
+
+  // Allocate space for storing the invoke's result temporarily (so
+  // that the helper function can return multiple values).  We don't
+  // need to do this if the result is unused, and we can't if its type
+  // is void.
+  Instruction *ResultAlloca = NULL;
+  if (!Invoke->use_empty()) {
+    ResultAlloca = new AllocaInst(Invoke->getType(), "invoke_result_ptr");
+    Func->getEntryBlock().getInstList().push_front(ResultAlloca);
+  }
+
+  // Create type for the helper function.
+  SmallVector<Type *, 10> ArgTypes;
+  for (unsigned I = 0, E = Invoke->getNumArgOperands(); I < E; ++I)
+    ArgTypes.push_back(Invoke->getArgOperand(I)->getType());
+  ArgTypes.push_back(Invoke->getCalledValue()->getType());
+  ArgTypes.push_back(FrameJmpBuf->getType());
+  if (ResultAlloca)
+    ArgTypes.push_back(Invoke->getType()->getPointerTo());
+  FunctionType *FTy = FunctionType::get(I32, ArgTypes, false);
+
+  // Create the helper function.
+  Function *HelperFunc = Function::Create(
+      FTy, GlobalValue::InternalLinkage, Func->getName() + "_setjmp_caller");
+  Func->getParent()->getFunctionList().insertAfter(Func, HelperFunc);
+  BasicBlock *EntryBB = BasicBlock::Create(Func->getContext(), "", HelperFunc);
+  BasicBlock *NormalBB = BasicBlock::Create(Func->getContext(), "normal",
+                                            HelperFunc);
+  BasicBlock *ExceptionBB = BasicBlock::Create(Func->getContext(), "exception",
+                                               HelperFunc);
+
+  // Unpack the helper function's arguments.
+  Function::arg_iterator ArgIter = HelperFunc->arg_begin();
+  SmallVector<Value *, 10> InnerCallArgs;
+  for (unsigned I = 0, E = Invoke->getNumArgOperands(); I < E; ++I) {
+    ArgIter->setName("arg");
+    InnerCallArgs.push_back(ArgIter++);
+  }
+  Argument *CalleeArg = ArgIter++;
+  Argument *JmpBufArg = ArgIter++;
+  CalleeArg->setName("func_ptr");
+  JmpBufArg->setName("jmp_buf");
+
+  // Create setjmp() call.
+  Value *SetjmpArgs[] = { JmpBufArg };
+  CallInst *SetjmpCall = CallInst::Create(SetjmpIntrinsic, SetjmpArgs,
+                                          "invoke_sj", EntryBB);
+  CopyDebug(SetjmpCall, Invoke);
+  // Setting the "returns_twice" attribute here prevents optimization
+  // passes from inlining HelperFunc into its caller.
+  SetjmpCall->setCanReturnTwice();
+  // Check setjmp()'s result.
+  Value *IsZero = CopyDebug(new ICmpInst(*EntryBB, CmpInst::ICMP_EQ, SetjmpCall,
+                                         ConstantInt::get(I32, 0),
+                                         "invoke_sj_is_zero"), Invoke);
+  CopyDebug(BranchInst::Create(NormalBB, ExceptionBB, IsZero, EntryBB), Invoke);
+  // Handle the normal, non-exceptional code path.
+  CallInst *InnerCall = CallInst::Create(CalleeArg, InnerCallArgs, "",
+                                         NormalBB);
+  CopyDebug(InnerCall, Invoke);
+  InnerCall->setAttributes(Invoke->getAttributes());
+  InnerCall->setCallingConv(Invoke->getCallingConv());
+  if (ResultAlloca) {
+    InnerCall->setName("result");
+    Argument *ResultArg = ArgIter++;
+    ResultArg->setName("result_ptr");
+    CopyDebug(new StoreInst(InnerCall, ResultArg, NormalBB), Invoke);
+  }
+  ReturnInst::Create(Func->getContext(), ConstantInt::get(I32, 0), NormalBB);
+  // Handle the exceptional code path.
+  ReturnInst::Create(Func->getContext(), ConstantInt::get(I32, 1), ExceptionBB);
+
+  // Create the outer call to the helper function.
+  SmallVector<Value *, 10> OuterCallArgs;
+  for (unsigned I = 0, E = Invoke->getNumArgOperands(); I < E; ++I)
+    OuterCallArgs.push_back(Invoke->getArgOperand(I));
+  OuterCallArgs.push_back(Invoke->getCalledValue());
+  OuterCallArgs.push_back(FrameJmpBuf);
+  if (ResultAlloca)
+    OuterCallArgs.push_back(ResultAlloca);
+  CallInst *OuterCall = CallInst::Create(HelperFunc, OuterCallArgs,
+                                         "invoke_is_exc", Invoke);
+  CopyDebug(OuterCall, Invoke);
+
+  // Retrieve the function return value stored in the alloca.  We only
+  // need to do this on the non-exceptional path, but we currently do
+  // it unconditionally because that is simpler.
+  if (ResultAlloca) {
+    Value *Result = new LoadInst(ResultAlloca, "", Invoke);
+    Result->takeName(Invoke);
+    Invoke->replaceAllUsesWith(Result);
+  }
+  return OuterCall;
+}
+
+static void convertInvokeToCall(InvokeInst *Invoke) {
+  SmallVector<Value*, 16> CallArgs(Invoke->op_begin(), Invoke->op_end() - 3);
+  // Insert a normal call instruction.
+  CallInst *NewCall = CallInst::Create(Invoke->getCalledValue(),
+                                       CallArgs, "", Invoke);
+  CopyDebug(NewCall, Invoke);
+  NewCall->takeName(Invoke);
+  NewCall->setCallingConv(Invoke->getCallingConv());
+  NewCall->setAttributes(Invoke->getAttributes());
+  Invoke->replaceAllUsesWith(NewCall);
+
+  // Insert an unconditional branch to the normal destination.
+  BranchInst::Create(Invoke->getNormalDest(), Invoke);
+  // Remove any PHI node entries from the exception destination.
+  Invoke->getUnwindDest()->removePredecessor(Invoke->getParent());
+  Invoke->eraseFromParent();
+}
+
+void FuncRewriter::expandInvokeInst(InvokeInst *Invoke) {
+  // Calls to ReturnsTwice functions, i.e. setjmp(), can't be moved
+  // into a helper function.  setjmp() can't throw an exception
+  // anyway, so convert the invoke to a call.
+  if (Invoke->hasFnAttr(Attribute::ReturnsTwice)) {
+    convertInvokeToCall(Invoke);
+    return;
+  }
+
+  initializeFrame();
+
+  LandingPadInst *LP = Invoke->getLandingPadInst();
+  Type *I32 = Type::getInt32Ty(Func->getContext());
+  Value *ExcInfo = ConstantInt::get(
+      I32, ExcInfoWriter->getIDForLandingPadClauseList(LP));
+
+  // Append the new frame to the list.
+  Value *OldList = CopyDebug(
+      new LoadInst(EHStackTlsVar, "old_eh_stack", Invoke), Invoke);
+  CopyDebug(new StoreInst(OldList, FrameNextPtr, Invoke), Invoke);
+  CopyDebug(new StoreInst(ExcInfo, FrameExcInfo, Invoke), Invoke);
+  CopyDebug(new StoreInst(Frame, EHStackTlsVar, Invoke), Invoke);
+  Value *IsException = createSetjmpWrappedCall(Invoke);
+  // Restore the old frame list.  We only need to do this on the
+  // non-exception code path, but we currently do it unconditionally
+  // because that is simpler.  (The PNaCl C++ runtime library restores
+  // the old frame list on the exceptional path; doing it again here
+  // redundantly is OK.)
+  CopyDebug(new StoreInst(OldList, EHStackTlsVar, Invoke), Invoke);
+
+  Value *IsZero = CopyDebug(new ICmpInst(Invoke, CmpInst::ICMP_EQ, IsException,
+                                         ConstantInt::get(I32, 0),
+                                         "invoke_sj_is_zero"), Invoke);
+  CopyDebug(BranchInst::Create(Invoke->getNormalDest(), Invoke->getUnwindDest(),
+                               IsZero, Invoke),
+            Invoke);
+
+  Invoke->eraseFromParent();
+}
+
+void FuncRewriter::expandResumeInst(ResumeInst *Resume) {
+  if (!EHResumeFunc) {
+    EHResumeFunc = Func->getParent()->getFunction("__pnacl_eh_resume");
+    if (!EHResumeFunc)
+      report_fatal_error("__pnacl_eh_resume() not defined");
+  }
+
+  // The "resume" instruction gets passed the landingpad's full result
+  // (struct LandingPadResult above).  Extract the exception_obj field
+  // to pass to __pnacl_eh_resume(), which doesn't need the
+  // matched_clause_id field.
+  unsigned Indexes[] = { 0 };
+  Value *ExceptionPtr =
+      CopyDebug(ExtractValueInst::Create(Resume->getValue(), Indexes,
+                                         "resume_exc", Resume), Resume);
+
+  // Cast to the pointer type that __pnacl_eh_resume() expects.
+  if (EHResumeFunc->getFunctionType()->getFunctionNumParams() != 1)
+    report_fatal_error("Bad type for __pnacl_eh_resume()");
+  Type *ArgType = EHResumeFunc->getFunctionType()->getFunctionParamType(0);
+  ExceptionPtr = new BitCastInst(ExceptionPtr, ArgType, "resume_cast", Resume);
+
+  Value *Args[] = { ExceptionPtr };
+  CopyDebug(CallInst::Create(EHResumeFunc, Args, "", Resume), Resume);
+  new UnreachableInst(Func->getContext(), Resume);
+  Resume->eraseFromParent();
+}
+
+void FuncRewriter::expandFunc() {
+  Type *I32 = Type::getInt32Ty(Func->getContext());
+
+  // We need to do two passes: When we process an invoke we need to
+  // look at its landingpad, so we can't remove the landingpads until
+  // all the invokes have been processed.
+  for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB) {
+    for (BasicBlock::iterator Iter = BB->begin(), E = BB->end(); Iter != E; ) {
+      Instruction *Inst = Iter++;
+      if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Inst)) {
+        expandInvokeInst(Invoke);
+      } else if (ResumeInst *Resume = dyn_cast<ResumeInst>(Inst)) {
+        expandResumeInst(Resume);
+      } else if (IntrinsicInst *Intrinsic = dyn_cast<IntrinsicInst>(Inst)) {
+        if (Intrinsic->getIntrinsicID() == Intrinsic::eh_typeid_for) {
+          Value *ExcType = Intrinsic->getArgOperand(0);
+          Value *Val = ConstantInt::get(
+              I32, ExcInfoWriter->getIDForExceptionType(ExcType));
+          Intrinsic->replaceAllUsesWith(Val);
+          Intrinsic->eraseFromParent();
+        }
+      }
+    }
+  }
+  for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB) {
+    for (BasicBlock::iterator Iter = BB->begin(), E = BB->end(); Iter != E; ) {
+      Instruction *Inst = Iter++;
+      if (LandingPadInst *LP = dyn_cast<LandingPadInst>(Inst)) {
+        initializeFrame();
+        Value *LPPtr = new BitCastInst(
+            FrameJmpBuf, LP->getType()->getPointerTo(), "landingpad_ptr", LP);
+        Value *LPVal = CopyDebug(new LoadInst(LPPtr, "", LP), LP);
+        LPVal->takeName(LP);
+        LP->replaceAllUsesWith(LPVal);
+        LP->eraseFromParent();
+      }
+    }
+  }
+}
+
+bool PNaClSjLjEH::runOnModule(Module &M) {
+  Type *JmpBufTy = ArrayType::get(Type::getInt8Ty(M.getContext()),
+                                  kPNaClJmpBufSize);
+
+  // Define "struct ExceptionFrame".
+  StructType *ExceptionFrameTy = StructType::create(M.getContext(),
+                                                    "ExceptionFrame");
+  Type *ExceptionFrameFields[] = {
+    JmpBufTy,  // jmp_buf
+    ExceptionFrameTy->getPointerTo(),  // struct ExceptionFrame *next
+    Type::getInt32Ty(M.getContext())  // Exception info (clause list ID)
+  };
+  ExceptionFrameTy->setBody(ExceptionFrameFields);
+
+  ExceptionInfoWriter ExcInfoWriter(&M.getContext());
+  for (Module::iterator Func = M.begin(), E = M.end(); Func != E; ++Func) {
+    FuncRewriter Rewriter(ExceptionFrameTy, &ExcInfoWriter, Func);
+    Rewriter.expandFunc();
+  }
+  ExcInfoWriter.defineGlobalVariables(&M);
+  return true;
+}
+
+ModulePass *llvm::createPNaClSjLjEHPass() {
+  return new PNaClSjLjEH();
+}