Пример #1
0
SILValue SILGenFunction::emitGlobalFunctionRef(SILLocation loc,
                                               SILDeclRef constant,
                                               SILConstantInfo constantInfo) {
  assert(constantInfo == getConstantInfo(constant));

  // Builtins must be fully applied at the point of reference.
  if (constant.hasDecl() &&
      isa<BuiltinUnit>(constant.getDecl()->getDeclContext())) {
    SGM.diagnose(loc.getSourceLoc(), diag::not_implemented,
                 "delayed application of builtin");
    return SILUndef::get(constantInfo.getSILType(), SGM.M);
  }
  
  // If the constant is a thunk we haven't emitted yet, emit it.
  if (!SGM.hasFunction(constant)) {
    if (constant.isCurried) {
      SGM.emitCurryThunk(constant);
    } else if (constant.isForeignToNativeThunk()) {
      SGM.emitForeignToNativeThunk(constant);
    } else if (constant.isNativeToForeignThunk()) {
      SGM.emitNativeToForeignThunk(constant);
    } else if (constant.kind == SILDeclRef::Kind::EnumElement) {
      SGM.emitEnumConstructor(cast<EnumElementDecl>(constant.getDecl()));
    }
  }

  auto f = SGM.getFunction(constant, NotForDefinition);
  assert(f->getLoweredFunctionType() == constantInfo.SILFnType);
  return B.createFunctionRef(loc, f);
}
Пример #2
0
/// Given that this is an 'Unknown' value, emit diagnostic notes providing
/// context about what the problem is.
void SymbolicValue::emitUnknownDiagnosticNotes(SILLocation fallbackLoc) {
  auto badInst = dyn_cast<SILInstruction>(getUnknownNode());
  if (!badInst)
    return;

  bool emittedFirstNote = emitNoteDiagnostic(badInst, getUnknownReason(),
                                             fallbackLoc);

  auto sourceLoc = fallbackLoc.getSourceLoc();
  auto &module = badInst->getModule();
  if (sourceLoc.isInvalid()) {
    diagnose(module.getASTContext(), sourceLoc, diag::constexpr_not_evaluable);
    return;
  }
  for (auto &sourceLoc : llvm::reverse(getUnknownCallStack())) {
    // Skip unknown sources.
    if (!sourceLoc.isValid())
      continue;

    auto diag = emittedFirstNote ? diag::constexpr_called_from
                                 : diag::constexpr_not_evaluable;
    diagnose(module.getASTContext(), sourceLoc, diag);
    emittedFirstNote = true;
  }
}
Пример #3
0
static void diagnoseReturn(const SILInstruction *I, ASTContext &Context) {
  auto *TI = dyn_cast<TermInst>(I);
  if (!TI || !(isa<BranchInst>(TI) || isa<ReturnInst>(TI)))
    return;

  const SILBasicBlock *BB = TI->getParent();
  const SILFunction *F = BB->getParent();

  // Warn if we reach a return inside a noreturn function.
  if (F->getLoweredFunctionType()->isNoReturn()) {
    SILLocation L = TI->getLoc();
    if (L.is<ReturnLocation>())
      diagnose(Context, L.getSourceLoc(), diag::return_from_noreturn);
    if (L.is<ImplicitReturnLocation>())
      diagnose(Context, L.getSourceLoc(), diag::return_from_noreturn);
  }
}
Пример #4
0
SILValue SILGenFunction::emitGlobalFunctionRef(SILLocation loc,
                                               SILDeclRef constant,
                                               SILConstantInfo constantInfo) {
  assert(constantInfo == getConstantInfo(constant));

  // Builtins must be fully applied at the point of reference.
  if (constant.hasDecl() &&
      isa<BuiltinUnit>(constant.getDecl()->getDeclContext())) {
    SGM.diagnose(loc.getSourceLoc(), diag::not_implemented,
                 "delayed application of builtin");
    return SILUndef::get(constantInfo.getSILType(), SGM.M);
  }
  
  // If the constant is a thunk we haven't emitted yet, emit it.
  if (!SGM.hasFunction(constant)) {
    if (constant.isCurried) {
      auto vd = constant.getDecl();
      // Reference the next uncurrying level of the function.
      SILDeclRef next = SILDeclRef(vd, constant.kind,
                                 SILDeclRef::ConstructAtBestResilienceExpansion,
                                 constant.uncurryLevel + 1);
      // If the function is fully uncurried and natively foreign, reference its
      // foreign entry point.
      if (!next.isCurried) {
        if (requiresForeignToNativeThunk(vd))
          next = next.asForeign();
      }
      
      // Preserve whether the curry thunks lead to a direct reference to the
      // method implementation.
      next = next.asDirectReference(constant.isDirectReference);

      SGM.emitCurryThunk(vd, constant, next);
    }
    // Otherwise, if this is a calling convention thunk we haven't emitted yet,
    // emit it.
    else if (constant.isForeignToNativeThunk()) {
      SGM.emitForeignToNativeThunk(constant);
    } else if (constant.isNativeToForeignThunk()) {
      SGM.emitNativeToForeignThunk(constant);
    } else if (constant.kind == SILDeclRef::Kind::EnumElement) {
      SGM.emitEnumConstructor(cast<EnumElementDecl>(constant.getDecl()));
    }
  }

  auto f = SGM.getFunction(constant, NotForDefinition);
  assert(f->getLoweredFunctionType() == constantInfo.SILFnType);
  return B.createFunctionRef(loc, f);
}
Пример #5
0
void swift::printSILLocationDescription(llvm::raw_ostream &out,
                                        SILLocation loc,
                                        ASTContext &Context) {
  if (loc.isNull()) {
    out << "<<invalid location>>";
  } else if (loc.isSILFile()) {
    printSourceLocDescription(out, loc.getSourceLoc(), Context);
  } else if (auto decl = loc.getAsASTNode<Decl>()) {
    printDeclDescription(out, decl, Context);
  } else if (auto expr = loc.getAsASTNode<Expr>()) {
    printExprDescription(out, expr, Context);
  } else if (auto stmt = loc.getAsASTNode<Stmt>()) {
    printStmtDescription(out, stmt, Context);
  } else if (auto pattern = loc.castToASTNode<Pattern>()) {
    printPatternDescription(out, pattern, Context);
  }
}
Пример #6
0
static void emitSourceLocationArgs(SILGenFunction &gen,
                                   SILLocation loc,
                                   ManagedValue (&args)[4]) {
  auto &ctx = gen.getASTContext();
  auto sourceLoc = loc.getSourceLoc();
  
  StringRef filename = "";
  unsigned line = 0;
  if (sourceLoc.isValid()) {
    unsigned bufferID = ctx.SourceMgr.findBufferContainingLoc(sourceLoc);
    filename = ctx.SourceMgr.getIdentifierForBuffer(bufferID);
    line = ctx.SourceMgr.getLineAndColumn(sourceLoc).first;
  }
  
  bool isASCII = true;
  for (unsigned char c : filename) {
    if (c > 127) {
      isASCII = false;
      break;
    }
  }
  
  auto wordTy = SILType::getBuiltinWordType(ctx);
  auto i1Ty = SILType::getBuiltinIntegerType(1, ctx);
  
  // File
  SILValue literal = gen.B.createStringLiteral(loc, filename,
                                             StringLiteralInst::Encoding::UTF8);
  args[0] = ManagedValue::forUnmanaged(literal);
  // File length
  literal = gen.B.createIntegerLiteral(loc, wordTy, filename.size());
  args[1] = ManagedValue::forUnmanaged(literal);
  // File is ascii
  literal = gen.B.createIntegerLiteral(loc, i1Ty, isASCII);
  args[2] = ManagedValue::forUnmanaged(literal);
  // Line
  literal = gen.B.createIntegerLiteral(loc, wordTy, line);
  args[3] = ManagedValue::forUnmanaged(literal);
}
Пример #7
0
/// \brief Issue an "unreachable code" diagnostic if the blocks contains or
/// leads to another block that contains user code.
///
/// Note, we rely on SILLocation information to determine if SILInstructions
/// correspond to user code.
static bool diagnoseUnreachableBlock(const SILBasicBlock &B,
                                     SILModule &M,
                                     const SILBasicBlockSet &Reachable,
                                     UnreachableUserCodeReportingState *State,
                                     const SILBasicBlock *TopLevelB,
                         llvm::SmallPtrSetImpl<const SILBasicBlock*> &Visited){
  if (Visited.count(&B))
    return false;
  Visited.insert(&B);
  
  assert(State);
  for (auto I = B.begin(), E = B.end(); I != E; ++I) {
    SILLocation Loc = I->getLoc();
    // If we've reached an implicit return, we have not found any user code and
    // can stop searching for it.
    if (Loc.is<ImplicitReturnLocation>() || Loc.isAutoGenerated())
      return false;

    // Check if the instruction corresponds to user-written code, also make
    // sure we don't report an error twice for the same instruction.
    if (isUserCode(&*I) && !State->BlocksWithErrors.count(&B)) {

      // Emit the diagnostic.
      auto BrInfoIter = State->MetaMap.find(TopLevelB);
      assert(BrInfoIter != State->MetaMap.end());
      auto BrInfo = BrInfoIter->second;

      switch (BrInfo.Kind) {
      case (UnreachableKind::FoldedBranch):
        // Emit the diagnostic on the unreachable block and emit the
        // note on the branch responsible for the unreachable code.
        diagnose(M.getASTContext(), Loc.getSourceLoc(), diag::unreachable_code);
        diagnose(M.getASTContext(), BrInfo.Loc.getSourceLoc(),
                 diag::unreachable_code_branch, BrInfo.CondIsAlwaysTrue);
        break;

      case (UnreachableKind::FoldedSwitchEnum): {
        // If we are warning about a switch condition being a constant, the main
        // emphasis should be on the condition (to ensure we have a single
        // message per switch).
        const SwitchStmt *SS = BrInfo.Loc.getAsASTNode<SwitchStmt>();
        if (!SS)
          break;
        assert(SS);
        const Expr *SE = SS->getSubjectExpr();
        diagnose(M.getASTContext(), SE->getLoc(), diag::switch_on_a_constant);
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diag::unreachable_code_note);
        break;
      }

      case (UnreachableKind::NoreturnCall): {
        // Specialcase when we are warning about unreachable code after a call
        // to a noreturn function.
        if (!BrInfo.Loc.isASTNode<ExplicitCastExpr>()) {
          assert(BrInfo.Loc.isASTNode<ApplyExpr>());
          diagnose(M.getASTContext(), Loc.getSourceLoc(),
                   diag::unreachable_code);
          diagnose(M.getASTContext(), BrInfo.Loc.getSourceLoc(),
                   diag::call_to_noreturn_note);
        }
        break;
      }
      }

      // Record that we've reported this unreachable block to avoid duplicates
      // in the future.
      State->BlocksWithErrors.insert(&B);
      return true;
    }
  }

  // This block could be empty if it's terminator has been folded.
  if (B.empty())
    return false;

  // If we have not found user code in this block, inspect it's successors.
  // Check if at least one of the successors contains user code.
  for (auto I = B.succ_begin(), E = B.succ_end(); I != E; ++I) {
    SILBasicBlock *SB = *I;
    bool HasReachablePred = false;
    for (auto PI = SB->pred_begin(), PE = SB->pred_end(); PI != PE; ++PI) {
      if (Reachable.count(*PI))
        HasReachablePred = true;
    }

    // If all of the predecessors of this successor are unreachable, check if
    // it contains user code.
    if (!HasReachablePred && diagnoseUnreachableBlock(*SB, M, Reachable,
                                                    State, TopLevelB, Visited))
      return true;
  }
  
  return false;
}
Пример #8
0
ManagedValue
SILGenFunction::emitPreconditionOptionalHasValue(SILLocation loc,
                                                 ManagedValue optional) {
  // Generate code to the optional is present, and if not, abort with a message
  // (provided by the stdlib).
  SILBasicBlock *contBB = createBasicBlock();
  SILBasicBlock *failBB = createBasicBlock();

  bool hadCleanup = optional.hasCleanup();
  bool hadLValue = optional.isLValue();

  auto noneDecl = getASTContext().getOptionalNoneDecl();
  auto someDecl = getASTContext().getOptionalSomeDecl();
  if (optional.getType().isAddress()) {
    // We forward in the creation routine for
    // unchecked_take_enum_data_addr. switch_enum_addr is a +0 operation.
    B.createSwitchEnumAddr(loc, optional.getValue(),
                           /*defaultDest*/ nullptr,
                           {{someDecl, contBB}, {noneDecl, failBB}});
  } else {
    B.createSwitchEnum(loc, optional.forward(*this),
                       /*defaultDest*/ nullptr,
                       {{someDecl, contBB}, {noneDecl, failBB}});
  }
  B.emitBlock(failBB);

  // Call the standard library implementation of _diagnoseUnexpectedNilOptional.
  if (auto diagnoseFailure =
        getASTContext().getDiagnoseUnexpectedNilOptional(nullptr)) {
    auto args = emitSourceLocationArgs(loc.getSourceLoc(), loc);
    
    emitApplyOfLibraryIntrinsic(loc, diagnoseFailure, SubstitutionMap(),
                                {
                                  args.filenameStartPointer,
                                  args.filenameLength,
                                  args.filenameIsAscii,
                                  args.line
                                },
                                SGFContext());
  }

  B.createUnreachable(loc);
  B.clearInsertionPoint();
  B.emitBlock(contBB);

  ManagedValue result;
  SILType payloadType = optional.getType().getAnyOptionalObjectType();

  if (payloadType.isObject()) {
    result = B.createOwnedPHIArgument(payloadType);
  } else {
    result =
        B.createUncheckedTakeEnumDataAddr(loc, optional, someDecl, payloadType);
  }

  if (hadCleanup) {
    return result;
  }

  if (hadLValue) {
    return ManagedValue::forLValue(result.forward(*this));
  }

  return ManagedValue::forUnmanaged(result.forward(*this));
}
Пример #9
0
static SILInstruction *constantFoldBuiltin(BuiltinInst *BI,
                                           Optional<bool> &ResultsInError) {
  const IntrinsicInfo &Intrinsic = BI->getIntrinsicInfo();
  SILModule &M = BI->getModule();

  // If it's an llvm intrinsic, fold the intrinsic.
  if (Intrinsic.ID != llvm::Intrinsic::not_intrinsic)
    return constantFoldIntrinsic(BI, Intrinsic.ID, ResultsInError);

  // Otherwise, it should be one of the builtin functions.
  OperandValueArrayRef Args = BI->getArguments();
  const BuiltinInfo &Builtin = BI->getBuiltinInfo();

  switch (Builtin.ID) {
  default: break;

// Check and fold binary arithmetic with overflow.
#define BUILTIN(id, name, Attrs)
#define BUILTIN_BINARY_OPERATION_WITH_OVERFLOW(id, name, _, attrs, overload) \
  case BuiltinValueKind::id:
#include "swift/AST/Builtins.def"
    return constantFoldBinaryWithOverflow(BI, Builtin.ID, ResultsInError);

#define BUILTIN(id, name, Attrs)
#define BUILTIN_BINARY_OPERATION(id, name, attrs, overload) \
case BuiltinValueKind::id:
#include "swift/AST/Builtins.def"
      return constantFoldBinary(BI, Builtin.ID, ResultsInError);

// Fold comparison predicates.
#define BUILTIN(id, name, Attrs)
#define BUILTIN_BINARY_PREDICATE(id, name, attrs, overload) \
case BuiltinValueKind::id:
#include "swift/AST/Builtins.def"
      return constantFoldCompare(BI, Builtin.ID);

  case BuiltinValueKind::Trunc:
  case BuiltinValueKind::ZExt:
  case BuiltinValueKind::SExt:
  case BuiltinValueKind::TruncOrBitCast:
  case BuiltinValueKind::ZExtOrBitCast:
  case BuiltinValueKind::SExtOrBitCast: {

    // We can fold if the value being cast is a constant.
    auto *V = dyn_cast<IntegerLiteralInst>(Args[0]);
    if (!V)
      return nullptr;

    APInt CastResV = constantFoldCast(V->getValue(), Builtin);

    // Add the literal instruction to represent the result of the cast.
    SILBuilderWithScope B(BI);
    return B.createIntegerLiteral(BI->getLoc(), BI->getType(), CastResV);
  }

  // Process special builtins that are designed to check for overflows in
  // integer conversions.
  case BuiltinValueKind::SToSCheckedTrunc:
  case BuiltinValueKind::UToUCheckedTrunc:
  case BuiltinValueKind::SToUCheckedTrunc:
  case BuiltinValueKind::UToSCheckedTrunc:
  case BuiltinValueKind::SUCheckedConversion:
  case BuiltinValueKind::USCheckedConversion: {
    return constantFoldAndCheckIntegerConversions(BI, Builtin, ResultsInError);
  }

  case BuiltinValueKind::IntToFPWithOverflow: {
    // Get the value. It should be a constant in most cases.
    // Note, this will not always be a constant, for example, when analyzing
    // _convertFromBuiltinIntegerLiteral function itself.
    auto *V = dyn_cast<IntegerLiteralInst>(Args[0]);
    if (!V)
      return nullptr;
    APInt SrcVal = V->getValue();
    Type DestTy = Builtin.Types[1];

    APFloat TruncVal(
        DestTy->castTo<BuiltinFloatType>()->getAPFloatSemantics());
    APFloat::opStatus ConversionStatus = TruncVal.convertFromAPInt(
        SrcVal, /*isSigned=*/true, APFloat::rmNearestTiesToEven);

    SILLocation Loc = BI->getLoc();
    const ApplyExpr *CE = Loc.getAsASTNode<ApplyExpr>();

    // Check for overflow.
    if (ConversionStatus & APFloat::opOverflow) {
      // If we overflow and are not asked for diagnostics, just return nullptr.
      if (!ResultsInError.hasValue())
        return nullptr;

      SmallString<10> SrcAsString;
      SrcVal.toString(SrcAsString, /*radix*/10, true /*isSigned*/);
      
      // Otherwise emit our diagnostics and then return nullptr.
      diagnose(M.getASTContext(), Loc.getSourceLoc(),
               diag::integer_literal_overflow,
               CE ? CE->getType() : DestTy, SrcAsString);
      ResultsInError = Optional<bool>(true);
      return nullptr;
    }

    // The call to the builtin should be replaced with the constant value.
    SILBuilderWithScope B(BI);
    return B.createFloatLiteral(Loc, BI->getType(), TruncVal);
  }

  case BuiltinValueKind::FPTrunc: {
    // Get the value. It should be a constant in most cases.
    auto *V = dyn_cast<FloatLiteralInst>(Args[0]);
    if (!V)
      return nullptr;
    APFloat TruncVal = V->getValue();
    Type DestTy = Builtin.Types[1];
    bool losesInfo;
    APFloat::opStatus ConversionStatus = TruncVal.convert(
        DestTy->castTo<BuiltinFloatType>()->getAPFloatSemantics(),
        APFloat::rmNearestTiesToEven, &losesInfo);
    SILLocation Loc = BI->getLoc();

    // Check if conversion was successful.
    if (ConversionStatus != APFloat::opStatus::opOK &&
        ConversionStatus != APFloat::opStatus::opInexact) {
      return nullptr;
    }

    // The call to the builtin should be replaced with the constant value.
    SILBuilderWithScope B(BI);
    return B.createFloatLiteral(Loc, BI->getType(), TruncVal);
  }

  case BuiltinValueKind::AssumeNonNegative: {
    auto *V = dyn_cast<IntegerLiteralInst>(Args[0]);
    if (!V)
      return nullptr;

    APInt VInt = V->getValue();
    if (VInt.isNegative() && ResultsInError.hasValue()) {
      diagnose(M.getASTContext(), BI->getLoc().getSourceLoc(),
               diag::wrong_non_negative_assumption,
               VInt.toString(/*Radix*/ 10, /*Signed*/ true));
      ResultsInError = Optional<bool>(true);
    }
    return V;
  }
  }
  return nullptr;
}
Пример #10
0
/// \brief Fold arithmetic intrinsics with overflow.
static SILInstruction *
constantFoldBinaryWithOverflow(BuiltinInst *BI, llvm::Intrinsic::ID ID,
                               bool ReportOverflow,
                               Optional<bool> &ResultsInError) {
  OperandValueArrayRef Args = BI->getArguments();
  assert(Args.size() >= 2);

  auto *Op1 = dyn_cast<IntegerLiteralInst>(Args[0]);
  auto *Op2 = dyn_cast<IntegerLiteralInst>(Args[1]);

  // If either Op1 or Op2 is not a literal, we cannot do anything.
  if (!Op1 || !Op2)
    return nullptr;

  // Calculate the result.
  APInt LHSInt = Op1->getValue();
  APInt RHSInt = Op2->getValue();
  bool Overflow;
  APInt Res = constantFoldBinaryWithOverflow(LHSInt, RHSInt, Overflow, ID);

  // If we can statically determine that the operation overflows,
  // warn about it if warnings are not disabled by ResultsInError being null.
  if (ResultsInError.hasValue() && Overflow && ReportOverflow) {
    // Try to infer the type of the constant expression that the user operates
    // on. If the intrinsic was lowered from a call to a function that takes
    // two arguments of the same type, use the type of the LHS argument.
    // This would detect '+'/'+=' and such.
    Type OpType;
    SILLocation Loc = BI->getLoc();
    const ApplyExpr *CE = Loc.getAsASTNode<ApplyExpr>();
    SourceRange LHSRange, RHSRange;
    if (CE) {
      const auto *Args = dyn_cast_or_null<TupleExpr>(CE->getArg());
      if (Args && Args->getNumElements() == 2) {
        // Look through inout types in order to handle += well.
        CanType LHSTy = Args->getElement(0)->getType()->getInOutObjectType()->
                         getCanonicalType();
        CanType RHSTy = Args->getElement(1)->getType()->getCanonicalType();
        if (LHSTy == RHSTy)
          OpType = Args->getElement(1)->getType();
        
        LHSRange = Args->getElement(0)->getSourceRange();
        RHSRange = Args->getElement(1)->getSourceRange();
      }
    }

    bool Signed = false;
    StringRef Operator = "+";
    
    switch (ID) {
      default: llvm_unreachable("Invalid case");
      case llvm::Intrinsic::sadd_with_overflow:
        Signed = true;
        break;
      case llvm::Intrinsic::uadd_with_overflow:
        break;
      case llvm::Intrinsic::ssub_with_overflow:
        Operator = "-";
        Signed = true;
        break;
      case llvm::Intrinsic::usub_with_overflow:
        Operator = "-";
        break;
      case llvm::Intrinsic::smul_with_overflow:
        Operator = "*";
        Signed = true;
        break;
      case llvm::Intrinsic::umul_with_overflow:
        Operator = "*";
        break;
    }

    if (!OpType.isNull()) {
      diagnose(BI->getModule().getASTContext(),
               Loc.getSourceLoc(),
               diag::arithmetic_operation_overflow,
               LHSInt.toString(/*Radix*/ 10, Signed),
               Operator,
               RHSInt.toString(/*Radix*/ 10, Signed),
               OpType).highlight(LHSRange).highlight(RHSRange);
    } else {
      // If we cannot get the type info in an expected way, describe the type.
      diagnose(BI->getModule().getASTContext(),
               Loc.getSourceLoc(),
               diag::arithmetic_operation_overflow_generic_type,
               LHSInt.toString(/*Radix*/ 10, Signed),
               Operator,
               RHSInt.toString(/*Radix*/ 10, Signed),
               Signed,
               LHSInt.getBitWidth()).highlight(LHSRange).highlight(RHSRange);
    }
    ResultsInError = Optional<bool>(true);
  }

  return constructResultWithOverflowTuple(BI, Res, Overflow);
}
Пример #11
0
static SILInstruction *
constantFoldAndCheckIntegerConversions(BuiltinInst *BI,
                                       const BuiltinInfo &Builtin,
                                       Optional<bool> &ResultsInError) {
  assert(Builtin.ID == BuiltinValueKind::SToSCheckedTrunc ||
         Builtin.ID == BuiltinValueKind::UToUCheckedTrunc ||
         Builtin.ID == BuiltinValueKind::SToUCheckedTrunc ||
         Builtin.ID == BuiltinValueKind::UToSCheckedTrunc ||
         Builtin.ID == BuiltinValueKind::SUCheckedConversion ||
         Builtin.ID == BuiltinValueKind::USCheckedConversion);

  // Check if we are converting a constant integer.
  OperandValueArrayRef Args = BI->getArguments();
  auto *V = dyn_cast<IntegerLiteralInst>(Args[0]);
  if (!V)
    return nullptr;
  APInt SrcVal = V->getValue();

  // Get source type and bit width.
  Type SrcTy = Builtin.Types[0];
  uint32_t SrcBitWidth =
    Builtin.Types[0]->castTo<BuiltinIntegerType>()->getGreatestWidth();

  // Compute the destination (for SrcBitWidth < DestBitWidth) and enough info
  // to check for overflow.
  APInt Result;
  bool OverflowError;
  Type DstTy;

  // Process conversions signed <-> unsigned for same size integers.
  if (Builtin.ID == BuiltinValueKind::SUCheckedConversion ||
      Builtin.ID == BuiltinValueKind::USCheckedConversion) {
    DstTy = SrcTy;
    Result = SrcVal;
    // Report an error if the sign bit is set.
    OverflowError = SrcVal.isNegative();

  // Process truncation from unsigned to signed.
  } else if (Builtin.ID != BuiltinValueKind::UToSCheckedTrunc) {
    assert(Builtin.Types.size() == 2);
    DstTy = Builtin.Types[1];
    uint32_t DstBitWidth =
      DstTy->castTo<BuiltinIntegerType>()->getGreatestWidth();
    //     Result = trunc_IntFrom_IntTo(Val)
    //   For signed destination:
    //     sext_IntFrom(Result) == Val ? Result : overflow_error
    //   For signed destination:
    //     zext_IntFrom(Result) == Val ? Result : overflow_error
    Result = SrcVal.trunc(DstBitWidth);
    // Get the signedness of the destination.
    bool Signed = (Builtin.ID == BuiltinValueKind::SToSCheckedTrunc);
    APInt Ext = Signed ? Result.sext(SrcBitWidth) : Result.zext(SrcBitWidth);
    OverflowError = (SrcVal != Ext);

  // Process the rest of truncations.
  } else {
    assert(Builtin.Types.size() == 2);
    DstTy = Builtin.Types[1];
    uint32_t DstBitWidth =
      Builtin.Types[1]->castTo<BuiltinIntegerType>()->getGreatestWidth();
    // Compute the destination (for SrcBitWidth < DestBitWidth):
    //   Result = trunc_IntTo(Val)
    //   Trunc  = trunc_'IntTo-1bit'(Val)
    //   zext_IntFrom(Trunc) == Val ? Result : overflow_error
    Result = SrcVal.trunc(DstBitWidth);
    APInt TruncVal = SrcVal.trunc(DstBitWidth - 1);
    OverflowError = (SrcVal != TruncVal.zext(SrcBitWidth));
  }

  // Check for overflow.
  if (OverflowError) {
    // If we are not asked to emit overflow diagnostics, just return nullptr on
    // overflow.
    if (!ResultsInError.hasValue())
      return nullptr;

    SILLocation Loc = BI->getLoc();
    SILModule &M = BI->getModule();
    const ApplyExpr *CE = Loc.getAsASTNode<ApplyExpr>();
    Type UserSrcTy;
    Type UserDstTy;
    // Primitive heuristics to get the user-written type.
    // Eventually we might be able to use SILLocation (when it contains info
    // about inlined call chains).
    if (CE) {
      if (const TupleType *RTy = CE->getArg()->getType()->getAs<TupleType>()) {
        if (RTy->getNumElements() == 1) {
          UserSrcTy = RTy->getElementType(0);
          UserDstTy = CE->getType();
        }
      } else {
        UserSrcTy = CE->getArg()->getType();
        UserDstTy = CE->getType();
      }
    }
    
 
    // Assume that we are converting from a literal if the Source size is
    // 2048. Is there a better way to identify conversions from literals?
    bool Literal = (SrcBitWidth == 2048);

    // FIXME: This will prevent hard error in cases the error is coming
    // from ObjC interoperability code. Currently, we treat NSUInteger as
    // Int.
    if (Loc.getSourceLoc().isInvalid()) {
      // Otherwise emit the appropriate diagnostic and set ResultsInError.
      if (Literal)
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diag::integer_literal_overflow_warn,
                 UserDstTy.isNull() ? DstTy : UserDstTy);
      else
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diag::integer_conversion_overflow_warn,
                 UserSrcTy.isNull() ? SrcTy : UserSrcTy,
                 UserDstTy.isNull() ? DstTy : UserDstTy);

      ResultsInError = Optional<bool>(true);
      return nullptr;
    }

    // Otherwise report the overflow error.
    if (Literal) {
      bool SrcTySigned, DstTySigned;
      std::tie(SrcTySigned, DstTySigned) = getTypeSignedness(Builtin);
      SmallString<10> SrcAsString;
      SrcVal.toString(SrcAsString, /*radix*/10, SrcTySigned);

      // Try to print user-visible types if they are available.
      if (!UserDstTy.isNull()) {
        auto diagID = diag::integer_literal_overflow;
        
        // If this is a negative literal in an unsigned type, use a specific
        // diagnostic.
        if (SrcTySigned && !DstTySigned && SrcVal.isNegative())
          diagID = diag::negative_integer_literal_overflow_unsigned;
        
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diagID, UserDstTy, SrcAsString);
      // Otherwise, print the Builtin Types.
      } else {
        bool SrcTySigned, DstTySigned;
        std::tie(SrcTySigned, DstTySigned) = getTypeSignedness(Builtin);
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diag::integer_literal_overflow_builtin_types,
                 DstTySigned, DstTy, SrcAsString);
      }
    } else {
      if (Builtin.ID == BuiltinValueKind::SUCheckedConversion) {
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diag::integer_conversion_sign_error,
                 UserDstTy.isNull() ? DstTy : UserDstTy);
      } else {
        // Try to print user-visible types if they are available.
        if (!UserSrcTy.isNull()) {
          diagnose(M.getASTContext(), Loc.getSourceLoc(),
                   diag::integer_conversion_overflow,
                   UserSrcTy, UserDstTy);

        // Otherwise, print the Builtin Types.
        } else {
          // Since builtin types are sign-agnostic, print the signedness
          // separately.
          bool SrcTySigned, DstTySigned;
          std::tie(SrcTySigned, DstTySigned) = getTypeSignedness(Builtin);
          diagnose(M.getASTContext(), Loc.getSourceLoc(),
                   diag::integer_conversion_overflow_builtin_types,
                   SrcTySigned, SrcTy, DstTySigned, DstTy);
        }
      }
    }

    ResultsInError = Optional<bool>(true);
    return nullptr;
  }

  // The call to the builtin should be replaced with the constant value.
  return constructResultWithOverflowTuple(BI, Result, false);

}