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diff --git a/lib/Transforms/NaCl/ExpandSmallArguments.cpp b/lib/Transforms/NaCl/ExpandSmallArguments.cpp
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+++ b/lib/Transforms/NaCl/ExpandSmallArguments.cpp
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+//===- ExpandSmallArguments.cpp - Expand out arguments smaller than i32----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// LLVM IR allows function return types and argument types such as
+// "zeroext i8" and "signext i8".  The Language Reference says that
+// zeroext "indicates to the code generator that the parameter or
+// return value should be zero-extended to the extent required by the
+// target's ABI (which is usually 32-bits, but is 8-bits for a i1 on
+// x86-64) by the caller (for a parameter) or the callee (for a return
+// value)".
+//
+// This can lead to non-portable behaviour when calling functions
+// without C prototypes or with wrong C prototypes.
+//
+// In order to remove this non-portability from PNaCl, and to simplify
+// the language that the PNaCl translator accepts, the
+// ExpandSmallArguments pass widens integer arguments and return types
+// to be at least 32 bits.  The pass inserts explicit cast
+// instructions (ZExtInst/SExtInst/TruncInst) as needed.
+//
+// The pass chooses between ZExtInst and SExtInst widening based on
+// whether a "signext" attribute is present.  However, in principle
+// the pass could always use zero-extension, because the extent to
+// which either zero-extension or sign-extension is done is up to the
+// target ABI, which is up to PNaCl to specify.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/Function.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 arguments' types.
+  class ExpandSmallArguments : public ModulePass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    ExpandSmallArguments() : ModulePass(ID) {
+      initializeExpandSmallArgumentsPass(*PassRegistry::getPassRegistry());
+    }
+
+    virtual bool runOnModule(Module &M);
+  };
+}
+
+char ExpandSmallArguments::ID = 0;
+INITIALIZE_PASS(ExpandSmallArguments, "expand-small-arguments",
+                "Expand function arguments to be at least 32 bits in size",
+                false, false)
+
+// Returns the normalized version of the given argument/return type.
+static Type *NormalizeType(Type *Ty) {
+  if (IntegerType *IntTy = dyn_cast<IntegerType>(Ty)) {
+    if (IntTy->getBitWidth() < 32) {
+      return IntegerType::get(Ty->getContext(), 32);
+    }
+  }
+  return Ty;
+}
+
+// Returns the normalized version of the given function type.
+static FunctionType *NormalizeFunctionType(FunctionType *FTy) {
+  if (FTy->isVarArg()) {
+    report_fatal_error(
+        "ExpandSmallArguments does not handle varargs functions");
+  }
+  SmallVector<Type *, 8> ArgTypes;
+  for (unsigned I = 0; I < FTy->getNumParams(); ++I) {
+    ArgTypes.push_back(NormalizeType(FTy->getParamType(I)));
+  }
+  return FunctionType::get(NormalizeType(FTy->getReturnType()),
+                           ArgTypes, false);
+}
+
+// Convert the given function to use normalized argument/return types.
+static bool ConvertFunction(Function *Func) {
+  FunctionType *FTy = Func->getFunctionType();
+  FunctionType *NFTy = NormalizeFunctionType(FTy);
+  if (NFTy == FTy)
+    return false; // No change needed.
+  Function *NewFunc = RecreateFunction(Func, NFTy);
+
+  // 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) {
+    NewArg->takeName(Arg);
+    if (Arg->getType() == NewArg->getType()) {
+      Arg->replaceAllUsesWith(NewArg);
+    } else {
+      Instruction *Trunc = new TruncInst(
+          NewArg, Arg->getType(), NewArg->getName() + ".arg_trunc",
+          NewFunc->getEntryBlock().getFirstInsertionPt());
+      Arg->replaceAllUsesWith(Trunc);
+    }
+  }
+
+  if (FTy->getReturnType() != NFTy->getReturnType()) {
+    // Fix up return instructions.
+    Instruction::CastOps CastType =
+        Func->getAttributes().hasAttribute(0, Attribute::SExt) ?
+        Instruction::SExt : Instruction::ZExt;
+    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 (ReturnInst *Ret = dyn_cast<ReturnInst>(Inst)) {
+          Value *Ext = CopyDebug(
+              CastInst::Create(CastType, Ret->getReturnValue(),
+                               NFTy->getReturnType(),
+                               Ret->getReturnValue()->getName() + ".ret_ext",
+                               Ret),
+              Ret);
+          CopyDebug(ReturnInst::Create(Ret->getContext(), Ext, Ret), Ret);
+          Ret->eraseFromParent();
+        }
+      }
+    }
+  }
+
+  Func->eraseFromParent();
+  return true;
+}
+
+// Convert the given call to use normalized argument/return types.
+static bool ConvertCall(CallInst *Call) {
+  // Don't try to change calls to intrinsics.
+  if (isa<IntrinsicInst>(Call))
+    return false;
+  FunctionType *FTy = cast<FunctionType>(
+      Call->getCalledValue()->getType()->getPointerElementType());
+  FunctionType *NFTy = NormalizeFunctionType(FTy);
+  if (NFTy == FTy)
+    return false; // No change needed.
+
+  // Convert arguments.
+  SmallVector<Value *, 8> Args;
+  for (unsigned I = 0; I < Call->getNumArgOperands(); ++I) {
+    Value *Arg = Call->getArgOperand(I);
+    if (NFTy->getParamType(I) != FTy->getParamType(I)) {
+      Instruction::CastOps CastType =
+          Call->getAttributes().hasAttribute(I + 1, Attribute::SExt) ?
+          Instruction::SExt : Instruction::ZExt;
+      Arg = CopyDebug(CastInst::Create(CastType, Arg, NFTy->getParamType(I),
+                                       "arg_ext", Call), Call);
+    }
+    Args.push_back(Arg);
+  }
+  Value *CastFunc =
+    CopyDebug(new BitCastInst(Call->getCalledValue(), NFTy->getPointerTo(),
+                              Call->getName() + ".arg_cast", Call), Call);
+  CallInst *NewCall = CallInst::Create(CastFunc, Args, "", Call);
+  CopyDebug(NewCall, Call);
+  NewCall->takeName(Call);
+  NewCall->setAttributes(Call->getAttributes());
+  NewCall->setCallingConv(Call->getCallingConv());
+  NewCall->setTailCall(Call->isTailCall());
+  Value *Result = NewCall;
+  if (FTy->getReturnType() != NFTy->getReturnType()) {
+    Result = CopyDebug(new TruncInst(NewCall, FTy->getReturnType(),
+                                     NewCall->getName() + ".ret_trunc",
+                                     Call), Call);
+  }
+  Call->replaceAllUsesWith(Result);
+  Call->eraseFromParent();
+  return true;
+}
+
+bool ExpandSmallArguments::runOnModule(Module &M) {
+  bool Changed = false;
+  for (Module::iterator Iter = M.begin(), E = M.end(); Iter != E; ) {
+    Function *Func = Iter++;
+    // Don't try to change intrinsic declarations because intrinsics
+    // will continue to have non-normalized argument types.  For
+    // example, memset() takes an i8 argument.  It shouldn't matter
+    // whether we modify the types of other function declarations, but
+    // we don't expect to see non-intrinsic function declarations in a
+    // PNaCl pexe.
+    if (Func->empty())
+      continue;
+
+    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 (CallInst *Call = dyn_cast<CallInst>(Inst)) {
+          Changed |= ConvertCall(Call);
+        } else if (isa<InvokeInst>(Inst)) {
+          report_fatal_error(
+              "ExpandSmallArguments does not handle invoke instructions");
+        }
+      }
+    }
+
+    Changed |= ConvertFunction(Func);
+  }
+  return Changed;
+}
+
+ModulePass *llvm::createExpandSmallArgumentsPass() {
+  return new ExpandSmallArguments();
+}