Rebased PNaCl localmods in LLVM to 223109

lib/Transforms/NaCl/ExpandVarArgs.cpp

+//===- ExpandVarArgs.cpp - Expand out variable argument function calls-----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass expands out all use of variable argument functions.
+//
+// This pass replaces a varargs function call with a function call in
+// which a pointer to the variable arguments is passed explicitly.
+// The callee explicitly allocates space for the variable arguments on
+// the stack using "alloca".
+//
+// Alignment:
+//
+// This pass does not add any alignment padding between the arguments
+// that are copied onto the stack.  This means that if the argument
+// list contains a mixture of, say, 1-byte and 4-byte values, the code
+// generated by this pass might be inefficient due to the memory
+// accesses being unaligned.
+//
+// This should only be an issue when passing structs as varargs
+// arguments.  We won't see i1, i8, i16 and float as varargs arguments
+// because the C standard requires the compiler to promote these to
+// the types "int" and "double".
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/NaCl.h"
+
+using namespace llvm;
+
+namespace {
+  // This is a ModulePass because the pass recreates functions in
+  // order to change their argument lists.
+  class ExpandVarArgs : public ModulePass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    ExpandVarArgs() : ModulePass(ID) {
+      initializeExpandVarArgsPass(*PassRegistry::getPassRegistry());
+    }
+
+    virtual bool runOnModule(Module &M);
+  };
+}
+
+char ExpandVarArgs::ID = 0;
+INITIALIZE_PASS(ExpandVarArgs, "expand-varargs",
+                "Expand out variable argument function definitions and calls",
+                false, false)
+
+static void ExpandVarArgFunc(Function *Func) {
+  Type *PtrType = Type::getInt8PtrTy(Func->getContext());
+
+  FunctionType *FTy = Func->getFunctionType();
+  SmallVector<Type *, 8> Params(FTy->param_begin(), FTy->param_end());
+  Params.push_back(PtrType);
+  FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false);
+  Function *NewFunc = RecreateFunction(Func, NFTy);
+
+  // Declare the new argument as "noalias".
+  NewFunc->setAttributes(
+      Func->getAttributes().addAttribute(
+          Func->getContext(), FTy->getNumParams() + 1, Attribute::NoAlias));
+
+  // Move the arguments across to the new function.
+  for (Function::arg_iterator Arg = Func->arg_begin(), E = Func->arg_end(),
+         NewArg = NewFunc->arg_begin();
+       Arg != E; ++Arg, ++NewArg) {
+    Arg->replaceAllUsesWith(NewArg);
+    NewArg->takeName(Arg);
+  }
+
+  Func->eraseFromParent();
+
+  Value *VarArgsArg = --NewFunc->arg_end();
+  VarArgsArg->setName("varargs");
+
+  // Expand out uses of llvm.va_start in this function.
+  for (Function::iterator BB = NewFunc->begin(), E = NewFunc->end();
+       BB != E;
+       ++BB) {
+    for (BasicBlock::iterator Iter = BB->begin(), E = BB->end();
+         Iter != E; ) {
+      Instruction *Inst = Iter++;
+      if (VAStartInst *VAS = dyn_cast<VAStartInst>(Inst)) {
+        Value *Cast = CopyDebug(new BitCastInst(VAS->getArgList(),
+                                                PtrType->getPointerTo(),
+                                                "arglist", VAS), VAS);
+        CopyDebug(new StoreInst(VarArgsArg, Cast, VAS), VAS);
+        VAS->eraseFromParent();
+      }
+    }
+  }
+}
+
+static void ExpandVAArgInst(VAArgInst *Inst) {
+  // Read the argument.  We assume that no realignment of the pointer
+  // is required.
+  Value *ArgList = CopyDebug(new BitCastInst(
+      Inst->getPointerOperand(),
+      Inst->getType()->getPointerTo()->getPointerTo(), "arglist", Inst), Inst);
+  Value *CurrentPtr = CopyDebug(new LoadInst(ArgList, "arglist_current", Inst),
+                                Inst);
+  Value *Result = CopyDebug(new LoadInst(CurrentPtr, "va_arg", Inst), Inst);
+  Result->takeName(Inst);
+
+  // Update the va_list to point to the next argument.
+  SmallVector<Value *, 1> Indexes;
+  Indexes.push_back(ConstantInt::get(Inst->getContext(), APInt(32, 1)));
+  Value *Next = CopyDebug(GetElementPtrInst::Create(
+                              CurrentPtr, Indexes, "arglist_next", Inst), Inst);
+  CopyDebug(new StoreInst(Next, ArgList, Inst), Inst);
+
+  Inst->replaceAllUsesWith(Result);
+  Inst->eraseFromParent();
+}
+
+static void ExpandVACopyInst(VACopyInst *Inst) {
+  // va_list may have more space reserved, but we only need to
+  // copy a single pointer.
+  Type *PtrTy = Type::getInt8PtrTy(Inst->getContext())->getPointerTo();
+  Value *Src = CopyDebug(new BitCastInst(Inst->getSrc(), PtrTy, "vacopy_src",
+                                         Inst), Inst);
+  Value *Dest = CopyDebug(new BitCastInst(Inst->getDest(), PtrTy, "vacopy_dest",
+                                          Inst), Inst);
+  Value *CurrentPtr = CopyDebug(new LoadInst(Src, "vacopy_currentptr", Inst),
+                                Inst);
+  CopyDebug(new StoreInst(CurrentPtr, Dest, Inst), Inst);
+  Inst->eraseFromParent();
+}
+
+static void LifetimeDecl(Intrinsic::ID id, Value *Ptr, Value *Size,
+                         Instruction *InsertPt) {
+  Module *M = InsertPt->getParent()->getParent()->getParent();
+  Value *Func = Intrinsic::getDeclaration(M, id);
+  SmallVector<Value *, 2> Args;
+  Args.push_back(Size);
+  Args.push_back(Ptr);
+  CallInst::Create(Func, Args, "", InsertPt);
+}
+
+// CopyCall() uses argument overloading so that it can be used by the
+// template ExpandVarArgCall().
+static CallInst *CopyCall(CallInst *Original, Value *Callee,
+                          ArrayRef<Value*> Args) {
+  return CallInst::Create(Callee, Args, "", Original);
+}
+
+static InvokeInst *CopyCall(InvokeInst *Original, Value *Callee,
+                            ArrayRef<Value*> Args) {
+  return InvokeInst::Create(Callee, Original->getNormalDest(),
+                            Original->getUnwindDest(), Args, "", Original);
+}
+
+// ExpandVarArgCall() converts a CallInst or InvokeInst to expand out
+// of varargs.  It returns whether the module was modified.
+template <class InstType>
+static bool ExpandVarArgCall(InstType *Call, DataLayout *DL) {
+  FunctionType *FuncType = cast<FunctionType>(
+      Call->getCalledValue()->getType()->getPointerElementType());
+  if (!FuncType->isFunctionVarArg())
+    return false;
+
+  LLVMContext *Context = &Call->getContext();
+
+  SmallVector<AttributeSet, 8> Attrs;
+  Attrs.push_back(Call->getAttributes().getFnAttributes());
+  Attrs.push_back(Call->getAttributes().getRetAttributes());
+
+  // Split argument list into fixed and variable arguments.
+  SmallVector<Value *, 8> FixedArgs;
+  SmallVector<Value *, 8> VarArgs;
+  SmallVector<Type *, 8> VarArgsTypes;
+  for (unsigned I = 0; I < FuncType->getNumParams(); ++I) {
+    FixedArgs.push_back(Call->getArgOperand(I));
+    // AttributeSets use 1-based indexing.
+    Attrs.push_back(Call->getAttributes().getParamAttributes(I + 1));
+  }
+  for (unsigned I = FuncType->getNumParams();
+       I < Call->getNumArgOperands(); ++I) {
+    Value *ArgVal = Call->getArgOperand(I);
+    VarArgs.push_back(ArgVal);
+    if (Call->getAttributes().hasAttribute(I + 1, Attribute::ByVal)) {
+      // For "byval" arguments we must dereference the pointer.
+      VarArgsTypes.push_back(ArgVal->getType()->getPointerElementType());
+    } else {
+      VarArgsTypes.push_back(ArgVal->getType());
+    }
+  }
+  if (VarArgsTypes.size() == 0) {
+    // Some buggy code (e.g. 176.gcc in Spec2k) uses va_arg on an
+    // empty argument list, which gives undefined behaviour in C.  To
+    // work around such programs, we create a dummy varargs buffer on
+    // the stack even though there are no arguments to put in it.
+    // This allows va_arg to read an undefined value from the stack
+    // rather than crashing by reading from an uninitialized pointer.
+    // An alternative would be to pass a null pointer to catch the
+    // invalid use of va_arg.
+    VarArgsTypes.push_back(Type::getInt32Ty(*Context));
+  }
+
+  // Create struct type for packing variable arguments into.  We
+  // create this as packed for now and assume that no alignment
+  // padding is desired.
+  StructType *VarArgsTy = StructType::get(*Context, VarArgsTypes, true);
+
+  // Allocate space for the variable argument buffer.  Do this at the
+  // start of the function so that we don't leak space if the function
+  // is called in a loop.
+  Function *Func = Call->getParent()->getParent();
+  Instruction *Buf = new AllocaInst(VarArgsTy, "vararg_buffer");
+  Func->getEntryBlock().getInstList().push_front(Buf);
+
+  // Call llvm.lifetime.start/end intrinsics to indicate that Buf is
+  // only used for the duration of the function call, so that the
+  // stack space can be reused elsewhere.
+  Type *I8Ptr = Type::getInt8Ty(*Context)->getPointerTo();
+  Instruction *BufPtr = new BitCastInst(Buf, I8Ptr, "vararg_lifetime_bitcast");
+  BufPtr->insertAfter(Buf);
+  Value *BufSize = ConstantInt::get(*Context,
+                                    APInt(64, DL->getTypeAllocSize(VarArgsTy)));
+  LifetimeDecl(Intrinsic::lifetime_start, BufPtr, BufSize, Call);
+
+  // Copy variable arguments into buffer.
+  int Index = 0;
+  for (SmallVector<Value *, 8>::iterator Iter = VarArgs.begin();
+       Iter != VarArgs.end();
+       ++Iter, ++Index) {
+    SmallVector<Value *, 2> Indexes;
+    Indexes.push_back(ConstantInt::get(*Context, APInt(32, 0)));
+    Indexes.push_back(ConstantInt::get(*Context, APInt(32, Index)));
+    Value *Ptr = CopyDebug(GetElementPtrInst::Create(
+                               Buf, Indexes, "vararg_ptr", Call), Call);
+    if (Call->getAttributes().hasAttribute(
+            FuncType->getNumParams() + Index + 1, Attribute::ByVal)) {
+      IRBuilder<> Builder(Call);
+      Builder.CreateMemCpy(
+          Ptr, *Iter,
+          DL->getTypeAllocSize((*Iter)->getType()->getPointerElementType()),
+          /* Align= */ 1);
+    } else {
+      CopyDebug(new StoreInst(*Iter, Ptr, Call), Call);
+    }
+  }
+
+  // Cast function to new type to add our extra pointer argument.
+  SmallVector<Type *, 8> ArgTypes(FuncType->param_begin(),
+                                  FuncType->param_end());
+  ArgTypes.push_back(VarArgsTy->getPointerTo());
+  FunctionType *NFTy = FunctionType::get(FuncType->getReturnType(),
+                                         ArgTypes, false);
+  Value *CastFunc =
+    CopyDebug(new BitCastInst(Call->getCalledValue(), NFTy->getPointerTo(),
+                              "vararg_func", Call), Call);
+
+  // Create the converted function call.
+  FixedArgs.push_back(Buf);
+  InstType *NewCall = CopyCall(Call, CastFunc, FixedArgs);
+  CopyDebug(NewCall, Call);
+  NewCall->setAttributes(AttributeSet::get(Call->getContext(), Attrs));
+  NewCall->takeName(Call);
+
+  if (isa<CallInst>(Call)) {
+    LifetimeDecl(Intrinsic::lifetime_end, BufPtr, BufSize, Call);
+  } else if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Call)) {
+    LifetimeDecl(Intrinsic::lifetime_end, BufPtr, BufSize,
+                 Invoke->getNormalDest()->getFirstInsertionPt());
+    LifetimeDecl(Intrinsic::lifetime_end, BufPtr, BufSize,
+                 Invoke->getUnwindDest()->getFirstInsertionPt());
+  }
+
+  Call->replaceAllUsesWith(NewCall);
+  Call->eraseFromParent();
+
+  return true;
+}
+
+bool ExpandVarArgs::runOnModule(Module &M) {
+  bool Changed = false;
+  DataLayout DL(&M);
+
+  for (Module::iterator Iter = M.begin(), E = M.end(); Iter != E; ) {
+    Function *Func = Iter++;
+
+    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 (VAArgInst *VI = dyn_cast<VAArgInst>(Inst)) {
+          Changed = true;
+          ExpandVAArgInst(VI);
+        } else if (isa<VAEndInst>(Inst)) {
+          // va_end() is a no-op in this implementation.
+          Changed = true;
+          Inst->eraseFromParent();
+        } else if (VACopyInst *VAC = dyn_cast<VACopyInst>(Inst)) {
+          Changed = true;
+          ExpandVACopyInst(VAC);
+        } else if (CallInst *Call = dyn_cast<CallInst>(Inst)) {
+          Changed |= ExpandVarArgCall(Call, &DL);
+        } else if (InvokeInst *Call = dyn_cast<InvokeInst>(Inst)) {
+          Changed |= ExpandVarArgCall(Call, &DL);
+        }
+      }
+    }
+
+    if (Func->isVarArg()) {
+      Changed = true;
+      ExpandVarArgFunc(Func);
+    }
+  }
+
+  return Changed;
+}
+
+ModulePass *llvm::createExpandVarArgsPass() {
+  return new ExpandVarArgs();
+}