PNaCl ABI: Promote illegal integer types

lib/Transforms/NaCl/PromoteIntegers.cpp

Index: lib/Transforms/NaCl/PromoteIntegers.cpp
diff --git a/lib/Transforms/NaCl/PromoteIntegers.cpp b/lib/Transforms/NaCl/PromoteIntegers.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..dd1f091c615702d169231bd4a6c759ee38bea1a6
--- /dev/null
+++ b/lib/Transforms/NaCl/PromoteIntegers.cpp
@@ -0,0 +1,613 @@
+//===- PromoteIntegers.cpp - Promote illegal integers for PNaCl ABI -------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+// A limited set of transformations to promote illegal-sized int types.
+//
+//===----------------------------------------------------------------------===//
+//
+// Legal sizes are currently 1, 8, 16, 32, 64 (and higher, see note below)
+// Operations on illegal integers and int pointers are be changed to operate
+// on the next-higher legal size.
+// It always maintains the invariant that the upper bits (above the size of the
+// original type) are zero; therefore after operations which can overwrite these
+// bits (e.g. add, shl, sext), the bits are cleared.
+//
+// Limitations:
+// 1) It can't change function signatures or global variables
+// 2) It won't promote (and can't expand) types larger than i64
+// 3) Doesn't support mul/div operators
+// 4) Doesn't handle arrays or structs (or GEPs) with illegal types
+// 5) Doesn't handle constant expressions
+//
+//===----------------------------------------------------------------------===//
+
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+namespace {
+class PromoteIntegers : public FunctionPass {
+ public:
+  static char ID;
+  PromoteIntegers() : FunctionPass(ID) {
+    initializePromoteIntegersPass(*PassRegistry::getPassRegistry());
+  }
+  virtual bool runOnFunction(Function &F);
+};
+}
+
+char PromoteIntegers::ID = 0;
+INITIALIZE_PASS(PromoteIntegers, "nacl-promote-ints",
+                "Promote integer types which are illegal in PNaCl",
+                false, false)
+
+
+// Legal sizes are currently 1, 8, 16, 32, and 64.
+// We can't yet expand types above 64 bit, so don't try to touch them for now.
+static bool isLegalSize(unsigned Size) {
+  // TODO(dschuff): expand >64bit types or disallow >64bit packed bitfields
+  if (Size > 64) return true;
+  return Size == 1 || Size == 8 || Size == 16 || Size == 32 || Size == 64;
+}
+
+static Type *getPromotedIntType(IntegerType *Ty) {
+  unsigned Width = Ty->getBitWidth();
+  assert(Width <= 64 && "Don't know how to legalize >64 bit types yet");
+  if (isLegalSize(Width))
+    return Ty;
+  return IntegerType::get(Ty->getContext(),
+                          Width < 8 ? 8 : NextPowerOf2(Width));
+}
+
+// Return a legal integer or pointer-to-integer type, promoting to a larger
+// size if necessary.
+static Type *getPromotedType(Type *Ty) {
+  assert((isa<IntegerType>(Ty) || isa<PointerType>(Ty)) &&
+         "Trying to convert a non-integer type");
+
+  if (isa<PointerType>(Ty))
+    return getPromotedIntType(
+        cast<IntegerType>(Ty->getContainedType(0)))->getPointerTo();
+
+  return getPromotedIntType(cast<IntegerType>(Ty));
+}
+
+// Return true if Val is an int or pointer-to-int which should be converted.
+static bool shouldConvert(Value *Val) {
+  Type *Ty = Val->getType();
+  if (PointerType *Pty = dyn_cast<PointerType>(Ty))
+    Ty = Pty->getContainedType(0);
+  if (IntegerType *ITy = dyn_cast<IntegerType>(Ty)) {
+    if (!isLegalSize(ITy->getBitWidth())) {
+      return true;
+    }
+  }
+  return false;
+}
+
+// Return a constant which has been promoted to a legal size.
+static Value *convertConstant(Constant *C, bool SignExt=false) {
+  assert(shouldConvert(C));
+  ConstantInt *CInt = cast<ConstantInt>(C);
+  return ConstantInt::get(
+      getPromotedType(cast<IntegerType>(CInt->getType())),
+      SignExt ? CInt->getSExtValue() : CInt->getZExtValue(),
+      /*isSigned=*/SignExt);
+}
+
+// Holds the state for converting/replacing values. Conversion is done in one
+// pass, with each value requiring conversion possibly having two stages. When
+// an instruction needs to be replaced (i.e. it has illegal operands or result)
+// a new instruction is created, and the pass calls getConverted to get its
+// operands. If the original operand has already been converted, the new value
+// is returned. Otherwise, a placeholder is created and used in the new
+// instruction. After a new instruction is created to replace an illegal one,
+// recordConverted is called to register the replacement. All users are updated,
+// and if there is a placeholder, its users are also updated.
+// recordConverted also queues the old value for deletion.
+// This strategy avoids the need for recursion or worklists for conversion.
+class ConversionState {
+ public:
+  // Return the promoted value for Val. If Val has not yet been converted,
+  // return a placeholder, which will be converted later.
+  Value *getConverted(Value *Val) {
+    if (!shouldConvert(Val))
+        return Val;
+    if (isa<GlobalVariable>(Val))
+      report_fatal_error("Can't convert illegal GlobalVariables");
+    if (RewrittenMap.count(Val))
+      return RewrittenMap[Val];
+    Value *P;
+    // Directly convert constants.
+    if (Constant *C = dyn_cast<Constant>(Val)) {
+      return convertConstant(C, /*SignExt=*/false);
+    } else {
+      // No converted value available yet, so create a placeholder.
+      P = new Argument(getPromotedType(Val->getType()));
+    }
+    RewrittenMap[Val] = P;
+    Placeholders[Val] = P;
+    return P;
+  }
+
+  // Replace the uses of From with To, replace the uses of any
+  // placeholders for From, and optionally give From's name to To.
+  // Also mark To for deletion.
+  void recordConverted(Instruction *From, Value *To, bool TakeName=true) {
+    ToErase.push_back(From);
+    if (!shouldConvert(From)) {
+      // From does not produce an illegal value, update its users in place.
+      From->replaceAllUsesWith(To);
+    } else {
+      // From produces an illegal value, so its users will be replaced. When
+      // replacements are created they will use values returned by getConverted.
+      if (Placeholders.count(From)) {
+        // Users of the placeholder can be updated in place.
+        Placeholders[From]->replaceAllUsesWith(To);
+        Placeholders.erase(From);
+      }
+      RewrittenMap[From] = To;
+    }
+    if (TakeName) {
+      To->takeName(From);
+    }
+  }
+
+  void eraseReplacedInstructions() {
+    for (SmallVectorImpl<Instruction *>::iterator I = ToErase.begin(),
+             E = ToErase.end(); I != E; ++I)
+      (*I)->dropAllReferences();
+    for (SmallVectorImpl<Instruction *>::iterator I = ToErase.begin(),
+             E = ToErase.end(); I != E; ++I)
+      (*I)->eraseFromParent();
+  }
+
+ private:
+  // Maps illegal values to their new converted values (or placeholders
+  // if no new value is available yet)
+  DenseMap<Value *, Value *> RewrittenMap;
+  // Maps illegal values with no conversion available yet to their placeholders
+  DenseMap<Value *, Value *> Placeholders;
+  // Illegal values which have already been converted, will be erased.
+  SmallVector<Instruction *, 8> ToErase;
+};
+
+// Split an illegal load into multiple legal loads and return the resulting
+// promoted value. The size of the load is assumed to be a multiple of 8.
+static Value *splitLoad(LoadInst *Inst, ConversionState &State) {
+  if (Inst->isVolatile() || Inst->isAtomic())
+    report_fatal_error("Can't split volatile/atomic loads");
+  if (cast<IntegerType>(Inst->getType())->getBitWidth() % 8 != 0)
+    report_fatal_error("Loads must be a multiple of 8 bits");
+
+  Value *OrigPtr = State.getConverted(Inst->getPointerOperand());
+  // OrigPtr is a placeholder in recursive calls, and so has no name
+  if (OrigPtr->getName().empty())
+    OrigPtr->setName(Inst->getPointerOperand()->getName());
+  unsigned Width = cast<IntegerType>(Inst->getType())->getBitWidth();
+  Type *NewType = getPromotedType(Inst->getType());
+  unsigned LoWidth = Width;
+
+  while (!isLegalSize(LoWidth)) LoWidth -= 8;
+  IntegerType *LoType = IntegerType::get(Inst->getContext(), LoWidth);
+  IntegerType *HiType = IntegerType::get(Inst->getContext(), Width - LoWidth);
+  IRBuilder<> IRB(Inst->getParent(), Inst);
+
+  Value *BCLo = IRB.CreateBitCast(
+      OrigPtr,
+      LoType->getPointerTo(),
+      OrigPtr->getName() + ".loty");
+  Value *LoadLo = IRB.CreateAlignedLoad(
+      BCLo, Inst->getAlignment(), Inst->getName() + ".lo");
+  Value *LoExt = IRB.CreateZExt(LoadLo, NewType, LoadLo->getName() + ".ext");
+  Value *GEPHi = IRB.CreateConstGEP1_32(BCLo, 1, OrigPtr->getName() + ".hi");
+  Value *BCHi = IRB.CreateBitCast(
+        GEPHi,
+        HiType->getPointerTo(),
+        OrigPtr->getName() + ".hity");
+
+  Value *LoadHi = IRB.CreateLoad(BCHi, Inst->getName() + ".hi");
+  if (!isLegalSize(Width - LoWidth)) {
+    LoadHi = splitLoad(cast<LoadInst>(LoadHi), State);
+    // BCHi was still illegal, and has been replaced with a placeholder in the
+    // recursive call. Since it is redundant with BCLo in the recursive call,
+    // just splice it out entirely.
+    State.recordConverted(cast<Instruction>(BCHi), GEPHi, /*TakeName=*/false);
+  }
+
+  Value *HiExt = IRB.CreateZExt(LoadHi, NewType, LoadHi->getName() + ".ext");
+  Value *HiShift = IRB.CreateShl(HiExt, LoWidth, HiExt->getName() + ".sh");
+  Value *Result = IRB.CreateOr(LoExt, HiShift);
+
+  State.recordConverted(Inst, Result);
+
+  return Result;
+}
+
+static Value *splitStore(StoreInst *Inst, ConversionState &State) {
+  if (Inst->isVolatile() || Inst->isAtomic())
+    report_fatal_error("Can't split volatile/atomic stores");
+  if (cast<IntegerType>(Inst->getValueOperand()->getType())->getBitWidth() % 8
+      != 0)
+    report_fatal_error("Stores must be a multiple of 8 bits");
+
+  Value *OrigPtr = State.getConverted(Inst->getPointerOperand());
+  // OrigPtr is now a placeholder in recursive calls, and so has no name.
+  if (OrigPtr->getName().empty())
+    OrigPtr->setName(Inst->getPointerOperand()->getName());
+  Value *OrigVal = State.getConverted(Inst->getValueOperand());
+  unsigned Width = cast<IntegerType>(
+      Inst->getValueOperand()->getType())->getBitWidth();
+  unsigned LoWidth = Width;
+
+  while (!isLegalSize(LoWidth)) LoWidth -= 8;
+  IntegerType *LoType = IntegerType::get(Inst->getContext(), LoWidth);
+  IntegerType *HiType = IntegerType::get(Inst->getContext(), Width - LoWidth);
+  IRBuilder<> IRB(Inst->getParent(), Inst);
+
+  Value *BCLo = IRB.CreateBitCast(
+      OrigPtr,
+      LoType->getPointerTo(),
+      OrigPtr->getName() + ".loty");
+  Value *LoTrunc = IRB.CreateTrunc(
+      OrigVal, LoType, OrigVal->getName() + ".lo");
+  IRB.CreateAlignedStore(LoTrunc, BCLo, Inst->getAlignment());
+
+  Value *HiLShr = IRB.CreateLShr(
+      OrigVal, LoWidth, OrigVal->getName() + ".hi.sh");
+  Value *GEPHi = IRB.CreateConstGEP1_32(BCLo, 1, OrigPtr->getName() + ".hi");
+  Value *HiTrunc = IRB.CreateTrunc(
+      HiLShr, HiType, OrigVal->getName() + ".hi");
+  Value *BCHi = IRB.CreateBitCast(
+        GEPHi,
+        HiType->getPointerTo(),
+        OrigPtr->getName() + ".hity");
+
+  Value *StoreHi = IRB.CreateStore(HiTrunc, BCHi);
+
+  if (!isLegalSize(Width - LoWidth)) {
+    // HiTrunc is still illegal, and is redundant with the truncate in the
+    // recursive call, so just get rid of it.
+    State.recordConverted(cast<Instruction>(HiTrunc), HiLShr,
+                          /*TakeName=*/false);
+    StoreHi = splitStore(cast<StoreInst>(StoreHi), State);
+    // BCHi was still illegal, and has been replaced with a placeholder in the
+    // recursive call. Since it is redundant with BCLo in the recursive call,
+    // just splice it out entirely.
+    State.recordConverted(cast<Instruction>(BCHi), GEPHi, /*TakeName=*/false);
+  }
+  State.recordConverted(Inst, StoreHi, /*TakeName=*/false);
+  return StoreHi;
+}
+
+// Return a value with the bits of the operand above the size of the original
+// type cleared. The operand is assumed to have been legalized already.
+static Value *getClearUpper(Value *Operand, Type *OrigType,
+                            Instruction *InsertPt) {
+  // If the operand is a constant, it will have been created by
+  // ConversionState.getConverted, which zero-extends by default.
+  if (isa<Constant>(Operand))
+    return Operand;
+  return BinaryOperator::Create(
+      Instruction::And,
+      Operand,
+      ConstantInt::get(
+          getPromotedType(OrigType),
+          APInt::getLowBitsSet(getPromotedType(OrigType)->getIntegerBitWidth(),
+                               OrigType->getIntegerBitWidth())),
+      Operand->getName() + ".clear",
+      InsertPt);
+}
+
+// Return a value with the bits of the operand above the size of the original
+// type equal to the sign bit of the original operand. The new operand is
+// assumed to have been legalized already.
+// This is done by shifting the sign bit of the smaller value up to the MSB
+// position in the larger size, and then arithmetic-shifting it back down.
+static Value *getSignExtend(Value *Operand, Value *OrigOperand,
+                            Instruction *InsertPt) {
+  // If OrigOperand was a constant, NewOperand will have been created by
+  // ConversionState.getConverted, which zero-extends by default. But that is
+  // wrong here, so replace it with a sign-extended constant.
+  if (Constant *C = dyn_cast<Constant>(OrigOperand))
+    return convertConstant(C, /*SignExt=*/true);
+  Type *OrigType = OrigOperand->getType();
+  ConstantInt *ShiftAmt = ConstantInt::getSigned(
+      cast<IntegerType>(getPromotedType(OrigType)),
+      getPromotedType(OrigType)->getIntegerBitWidth() -
+        OrigType->getIntegerBitWidth());
+  BinaryOperator *Shl = BinaryOperator::Create(
+      Instruction::Shl,
+      Operand,
+      ShiftAmt,
+      Operand->getName() + ".getsign",
+      InsertPt);
+  return BinaryOperator::Create(
+      Instruction::AShr,
+      Shl,
+      ShiftAmt,
+      Operand->getName() + ".signed",
+      InsertPt);
+}
+
+static void convertInstruction(Instruction *Inst, ConversionState &State) {
+  if (SExtInst *Sext = dyn_cast<SExtInst>(Inst)) {
+    Value *Op = Sext->getOperand(0);
+    Value *NewInst = NULL;
+    // If the operand to be extended is illegal, we first need to fill its
+    // upper bits (which are zero) with its sign bit.
+    if (shouldConvert(Op)) {
+      NewInst = getSignExtend(State.getConverted(Op), Op, Sext);
+    }
+    // If the converted type of the operand is the same as the converted
+    // type of the result, we won't actually be changing the type of the
+    // variable, just its value.
+    if (getPromotedType(Op->getType()) !=
+        getPromotedType(Sext->getType())) {
+      NewInst = new SExtInst(
+          NewInst ? NewInst : State.getConverted(Op),
+          getPromotedType(cast<IntegerType>(Sext->getType())),
+          Sext->getName() + ".sext", Sext);
+    }
+    // Now all the bits of the result are correct, but we need to restore
+    // the bits above its type to zero.
+    if (shouldConvert(Sext)) {
+      NewInst = getClearUpper(NewInst, Sext->getType(), Sext);
+    }
+    assert(NewInst && "Failed to convert sign extension");
+    State.recordConverted(Sext, NewInst);
+  } else if (ZExtInst *Zext = dyn_cast<ZExtInst>(Inst)) {
+    Value *Op = Zext->getOperand(0);
+    Value *NewInst = NULL;
+    // TODO(dschuff): Some of these zexts could be no-ops.
+    if (shouldConvert(Op)) {
+      NewInst = getClearUpper(State.getConverted(Op),
+                              Op->getType(),
+                              Zext);
+    }
+    // If the converted type of the operand is the same as the converted
+    // type of the result, we won't actually be changing the type of the
+    // variable, just its value.
+    if (getPromotedType(Op->getType()) !=
+        getPromotedType(Zext->getType())) {
+      NewInst = CastInst::CreateZExtOrBitCast(
+          NewInst ? NewInst : State.getConverted(Op),
+          getPromotedType(cast<IntegerType>(Zext->getType())),
+          "", Zext);
+    }
+    assert(NewInst);
+    State.recordConverted(Zext, NewInst);
+  } else if (TruncInst *Trunc = dyn_cast<TruncInst>(Inst)) {
+    Value *Op = Trunc->getOperand(0);
+    Value *NewInst = NULL;
+    // If the converted type of the operand is the same as the converted
+    // type of the result, we won't actually be changing the type of the
+    // variable, just its value.
+    if (getPromotedType(Op->getType()) !=
+        getPromotedType(Trunc->getType())) {
+      NewInst = new TruncInst(
+          State.getConverted(Op),
+          getPromotedType(cast<IntegerType>(Trunc->getType())),
+          State.getConverted(Op)->getName() + ".trunc",
+          Trunc);
+    }
+    // Restoring the upper-bits-are-zero invariant effectively truncates the
+    // value.
+    if (shouldConvert(Trunc)) {
+      NewInst = getClearUpper(NewInst ? NewInst : Op,
+                              Trunc->getType(),
+                              Trunc);
+    }
+    assert(NewInst);
+    State.recordConverted(Trunc, NewInst);
+  } else if (AllocaInst *Alloc = dyn_cast<AllocaInst>(Inst)) {
+    // Don't handle arrays of illegal types, but we could handle an array
+    // with size specified as an illegal type, as unlikely as that seems.
+    if (shouldConvert(Alloc) && Alloc->isArrayAllocation())
+      report_fatal_error("Can't convert arrays of illegal type");
+    AllocaInst *NewInst = new AllocaInst(
+        getPromotedType(Alloc->getAllocatedType()),
+        State.getConverted(Alloc->getArraySize()),
+        "", Alloc);
+    NewInst->setAlignment(Alloc->getAlignment());
+    State.recordConverted(Alloc, NewInst);
+  } else if (BitCastInst *BCInst = dyn_cast<BitCastInst>(Inst)) {
+    // Only handle pointers. Ints can't be casted to/from other ints
+    if (shouldConvert(BCInst) || shouldConvert(BCInst->getOperand(0))) {
+      BitCastInst *NewInst = new BitCastInst(
+          State.getConverted(BCInst->getOperand(0)),
+          getPromotedType(BCInst->getDestTy()),
+          "", BCInst);
+      State.recordConverted(BCInst, NewInst);
+    }
+  } else if (LoadInst *Load = dyn_cast<LoadInst>(Inst)) {
+    if (shouldConvert(Load)) {
+      splitLoad(Load, State);
+    }
+  } else if (StoreInst *Store = dyn_cast<StoreInst>(Inst)) {
+    if (shouldConvert(Store->getValueOperand())) {
+      splitStore(Store, State);
+    }
+  } else if (CallInst *Call = dyn_cast<CallInst>(Inst)) {
+    report_fatal_error("can't convert calls with illegal types");
+  } else if (BinaryOperator *Binop = dyn_cast<BinaryOperator>(Inst)) {
+    Value *NewInst = NULL;
+    if (Binop->getOpcode() == Instruction::AShr) {
+      // The AShr operand needs to be sign-extended to the promoted size
+      // before shifting. Because the sign-extension is implemented with
+      // with AShr, it can be combined with the original operation.
+      Value *Op = Binop->getOperand(0);
+      Value *ShiftAmount = NULL;
+      APInt SignShiftAmt = APInt(
+          getPromotedType(Op->getType())->getIntegerBitWidth(),
+          getPromotedType(Op->getType())->getIntegerBitWidth() -
+          Op->getType()->getIntegerBitWidth());
+      NewInst = BinaryOperator::Create(
+          Instruction::Shl,
+          State.getConverted(Op),
+          ConstantInt::get(getPromotedType(Op->getType()), SignShiftAmt),
+          State.getConverted(Op)->getName() + ".getsign",
+          Binop);
+      if (ConstantInt *C = dyn_cast<ConstantInt>(
+              State.getConverted(Binop->getOperand(1)))) {
+        ShiftAmount = ConstantInt::get(getPromotedType(Op->getType()),
+                                       SignShiftAmt + C->getValue());
+      } else {
+        ShiftAmount = BinaryOperator::Create(
+            Instruction::Add,
+            State.getConverted(Binop->getOperand(1)),
+            ConstantInt::get(
+                getPromotedType(Binop->getOperand(1)->getType()),
+                SignShiftAmt),
+            State.getConverted(Op)->getName() + ".shamt", Binop);
+      }
+      NewInst = BinaryOperator::Create(
+          Instruction::AShr,
+          NewInst,
+          ShiftAmount,
+          Binop->getName() + ".result", Binop);
+    } else {
+      // If the original operation is not AShr, just recreate it as usual.
+      NewInst = BinaryOperator::Create(
+          Binop->getOpcode(),
+          State.getConverted(Binop->getOperand(0)),
+          State.getConverted(Binop->getOperand(1)),
+          Binop->getName() + ".result", Binop);
+      if (isa<OverflowingBinaryOperator>(NewInst)) {
+        cast<BinaryOperator>(NewInst)->setHasNoUnsignedWrap
+            (Binop->hasNoUnsignedWrap());
+        cast<BinaryOperator>(NewInst)->setHasNoSignedWrap(
+            Binop->hasNoSignedWrap());
+      }
+    }
+
+    // Now restore the invariant if necessary.
+    // This switch also sanity-checks the operation.
+    switch (Binop->getOpcode()) {
+      case Instruction::And:
+      case Instruction::Or:
+      case Instruction::Xor:
+      case Instruction::LShr:
+        // These won't change the upper bits.
+        break;
+        // These can change the upper bits, unless we are sure they never
+        // overflow. So clear them now.
+      case Instruction::Add:
+      case Instruction::Sub:
+        if (!(Binop->hasNoUnsignedWrap() && Binop->hasNoSignedWrap()))
+          NewInst = getClearUpper(NewInst, Binop->getType(), Binop);
+        break;
+      case Instruction::Shl:
+        if (!Binop->hasNoUnsignedWrap())
+          NewInst = getClearUpper(NewInst, Binop->getType(), Binop);
+        break;
+        // We modified the upper bits ourselves when implementing AShr
+      case Instruction::AShr:
+        NewInst = getClearUpper(NewInst, Binop->getType(), Binop);
+        break;
+        // We should not see FP operators here.
+        // We don't handle mul/div.
+      case Instruction::FAdd:
+      case Instruction::FSub:
+      case Instruction::Mul:
+      case Instruction::FMul:
+      case Instruction::UDiv:
+      case Instruction::SDiv:
+      case Instruction::FDiv:
+      case Instruction::URem:
+      case Instruction::SRem:
+      case Instruction::FRem:
+      case Instruction::BinaryOpsEnd:
+        errs() << *Inst << "\n";
+        llvm_unreachable("Cannot handle binary operator");
+        break;
+    }
+
+    State.recordConverted(Binop, NewInst);
+  } else if (ICmpInst *Cmp = dyn_cast<ICmpInst>(Inst)) {
+    Value *Op0, *Op1;
+    // For signed compares, operands are sign-extended to their
+    // promoted type. For unsigned or equality compares, the comparison
+    // is equivalent with the larger type because they are already
+    // zero-extended.
+    if (Cmp->isSigned()) {
+      Op0 = getSignExtend(State.getConverted(Cmp->getOperand(0)),
+                          Cmp->getOperand(0),
+                          Cmp);
+      Op1 = getSignExtend(State.getConverted(Cmp->getOperand(1)),
+                          Cmp->getOperand(1),
+                          Cmp);
+    } else {
+      Op0 = State.getConverted(Cmp->getOperand(0));
+      Op1 = State.getConverted(Cmp->getOperand(1));
+    }
+    ICmpInst *NewInst = new ICmpInst(
+        Cmp, Cmp->getPredicate(), Op0, Op1, "");
+    State.recordConverted(Cmp, NewInst);
+  } else if (SelectInst *Select = dyn_cast<SelectInst>(Inst)) {
+    SelectInst *NewInst = SelectInst::Create(
+        Select->getCondition(),
+        State.getConverted(Select->getTrueValue()),
+        State.getConverted(Select->getFalseValue()),
+        "", Select);
+    State.recordConverted(Select, NewInst);
+  } else if (PHINode *Phi = dyn_cast<PHINode>(Inst)) {
+    PHINode *NewPhi = PHINode::Create(
+        getPromotedType(Phi->getType()),
+        Phi->getNumIncomingValues(),
+        "", Phi);
+    for (unsigned I = 0, E = Phi->getNumIncomingValues(); I < E; ++I) {
+      NewPhi->addIncoming(State.getConverted(Phi->getIncomingValue(I)),
+                          Phi->getIncomingBlock(I));
+    }
+    State.recordConverted(Phi, NewPhi);
+  } else {
+    errs() << *Inst<<"\n";
+    llvm_unreachable("unhandled instruction");
+  }
+}
+
+bool PromoteIntegers::runOnFunction(Function &F) {
+  // Don't support changing the function arguments. This should not be
+  // generated by clang.
+  for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I) {
+    Value *Arg = I;
+    if (shouldConvert(Arg)) {
+      errs() << "Function " << F.getName() << ": " << *Arg << "\n";
+      llvm_unreachable("Function has illegal integer/pointer argument");
+    }
+  }
+
+  ConversionState State;
+  bool Modified = false;
+  for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
+    for (BasicBlock::iterator BBI = FI->begin(), BBE = FI->end(); BBI != BBE;) {
+      Instruction *Inst = BBI++;
+      // Only attempt to convert an instruction if its result or any of its
+      // operands are illegal.
+      bool ShouldConvert = shouldConvert(Inst);
+      for (User::op_iterator OI = Inst->op_begin(), OE = Inst->op_end();
+           OI != OE; ++OI)
+        ShouldConvert |= shouldConvert(cast<Value>(OI));
+
+      if (ShouldConvert) {
+        convertInstruction(Inst, State);
+        Modified = true;
+      }
+    }
+  }
+  State.eraseReplacedInstructions();
+  return Modified;
+}