lib/Analysis/Verifier.cpp

//===- Verifier.cpp - MLIR Verifier Implementation ------------------------===//
//
// Copyright 2019 The MLIR Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// =============================================================================
//
// This file implements the verify() methods on the various IR types, performing
// (potentially expensive) checks on the holistic structure of the code.  This
// can be used for detecting bugs in compiler transformations and hand written
// .mlir files.
//
// The checks in this file are only for things that can occur as part of IR
// transformations: e.g. violation of dominance information, malformed operation
// attributes, etc.  MLIR supports transformations moving IR through locally
// invalid states (e.g. unlinking an instruction from an instruction before
// re-inserting it in a new place), but each transformation must complete with
// the IR in a valid form.
//
// This should not check for things that are always wrong by construction (e.g.
// affine maps or other immutable structures that are incorrect), because those
// are not mutable and can be checked at time of construction.
//
//===----------------------------------------------------------------------===//

#include "mlir/Analysis/Dominance.h"
#include "mlir/IR/Attributes.h"
#include "mlir/IR/Dialect.h"
#include "mlir/IR/Function.h"
#include "mlir/IR/Instruction.h"
#include "mlir/IR/Module.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/PrettyStackTrace.h"
#include "llvm/Support/Regex.h"
#include "llvm/Support/raw_ostream.h"
using namespace mlir;

namespace {
/// This class encapsulates all the state used to verify a function body.  It is
/// a pervasive truth that this file treats "true" as an error that needs to be
/// recovered from, and "false" as success.
///
class FuncVerifier {
public:
  bool failure(const Twine &message, Instruction &value) {
    return value.emitError(message);
  }

  bool failure(const Twine &message, Function &fn) {
    return fn.emitError(message);
  }

  bool failure(const Twine &message, Block &bb) {
    // Take the location information for the first instruction in the block.
    if (!bb.empty())
      return failure(message, bb.front());

    // Worst case, fall back to using the function's location.
    return failure(message, fn);
  }

  /// Returns the registered dialect for a dialect-specific attribute.
  template <typename ErrorContext>
  Dialect *getDialectForAttribute(const NamedAttribute &attr,
                                  const ErrorContext &ctx) {
    assert(attr.first.strref().contains('.') && "expected dialect attribute");
    auto dialectNamePair = attr.first.strref().split('.');
    return fn.getContext()->getRegisteredDialect(dialectNamePair.first);
  }

  template <typename ErrorContext>
  bool verifyAttribute(Attribute attr, ErrorContext &ctx) {
    if (!attr.isOrContainsFunction())
      return false;

    // If we have a function attribute, check that it is non-null and in the
    // same module as the operation that refers to it.
    if (auto fnAttr = attr.dyn_cast<FunctionAttr>()) {
      if (!fnAttr.getValue())
        return failure("attribute refers to deallocated function!", ctx);

      if (fnAttr.getValue()->getModule() != fn.getModule())
        return failure("attribute refers to function '" +
                           Twine(fnAttr.getValue()->getName()) +
                           "' defined in another module!",
                       ctx);
      return false;
    }

    // Otherwise, we must have an array attribute, remap the elements.
    for (auto elt : attr.cast<ArrayAttr>().getValue()) {
      if (verifyAttribute(elt, ctx))
        return true;
    }

    return false;
  }

  bool verify();
  bool verifyBlock(Block &block, bool isTopLevel);
  bool verifyOperation(Instruction &op);
  bool verifyDominance(Block &block);
  bool verifyInstDominance(Instruction &inst);

  explicit FuncVerifier(Function &fn)
      : fn(fn), identifierRegex("^[a-zA-Z_][a-zA-Z_0-9\\.\\$]*$") {}

private:
  /// The function being checked.
  Function &fn;

  /// Dominance information for this function, when checking dominance.
  DominanceInfo *domInfo = nullptr;

  /// Regex checker for attribute names.
  llvm::Regex identifierRegex;
};
} // end anonymous namespace

bool FuncVerifier::verify() {
  llvm::PrettyStackTraceFormat fmt("MLIR Verifier: func @%s",
                                   fn.getName().c_str());

  // Check that the function name is valid.
  if (!identifierRegex.match(fn.getName().strref()))
    return failure("invalid function name '" + fn.getName().strref() + "'", fn);

  /// Verify that all of the attributes are okay.
  for (auto attr : fn.getAttrs()) {
    if (!identifierRegex.match(attr.first))
      return failure("invalid attribute name '" + attr.first.strref() + "'",
                     fn);
    if (verifyAttribute(attr.second, fn))
      return true;

    /// Check that the attribute is a dialect attribute, i.e. contains a '.' for
    /// the namespace.
    if (!attr.first.strref().contains('.'))
      return failure("functions may only have dialect attributes", fn);

    // Verify this attribute with the defining dialect.
    if (auto *dialect = getDialectForAttribute(attr, fn))
      if (dialect->verifyFunctionAttribute(&fn, attr))
        return true;
  }

  /// Verify that all of the argument attributes are okay.
  for (unsigned i = 0, e = fn.getNumArguments(); i != e; ++i) {
    for (auto attr : fn.getArgAttrs(i)) {
      if (!identifierRegex.match(attr.first))
        return failure(
            llvm::formatv("invalid attribute name '{0}' on argument {1}",
                          attr.first.strref(), i),
            fn);
      if (verifyAttribute(attr.second, fn))
        return true;

      /// Check that the attribute is a dialect attribute, i.e. contains a '.'
      /// for the namespace.
      if (!attr.first.strref().contains('.'))
        return failure("function arguments may only have dialect attributes",
                       fn);

      // Verify this attribute with the defining dialect.
      if (auto *dialect = getDialectForAttribute(attr, fn))
        if (dialect->verifyFunctionArgAttribute(&fn, i, attr))
          return true;
    }
  }

  // External functions have nothing more to check.
  if (fn.isExternal())
    return false;

  // Verify the first block has no predecessors.
  auto *firstBB = &fn.front();
  if (!firstBB->hasNoPredecessors())
    return failure("entry block of function may not have predecessors", fn);

  // Verify that the argument list of the function and the arg list of the first
  // block line up.
  auto fnInputTypes = fn.getType().getInputs();
  if (fnInputTypes.size() != firstBB->getNumArguments())
    return failure("first block of function must have " +
                       Twine(fnInputTypes.size()) +
                       " arguments to match function signature",
                   fn);
  for (unsigned i = 0, e = firstBB->getNumArguments(); i != e; ++i)
    if (fnInputTypes[i] != firstBB->getArgument(i)->getType())
      return failure(
          "type of argument #" + Twine(i) +
              " must match corresponding argument in function signature",
          fn);

  for (auto &block : fn)
    if (verifyBlock(block, /*isTopLevel=*/true))
      return true;

  // Since everything looks structurally ok to this point, we do a dominance
  // check.  We do this as a second pass since malformed CFG's can cause
  // dominator analysis constructure to crash and we want the verifier to be
  // resilient to malformed code.
  DominanceInfo theDomInfo(const_cast<Function *>(&fn));
  domInfo = &theDomInfo;
  for (auto &block : fn)
    if (verifyDominance(block))
      return true;

  domInfo = nullptr;
  return false;
}

// Returns if the given block is allowed to have no terminator.
static bool canBlockHaveNoTerminator(Block &block) {
  // Allow the first block of an operation region to have no terminator if it is
  // the only block in the region.
  auto *parentList = block.getParent();
  return parentList->getContainingInst() &&
         std::next(parentList->begin()) == parentList->end();
}

bool FuncVerifier::verifyBlock(Block &block, bool isTopLevel) {
  for (auto *arg : block.getArguments()) {
    if (arg->getOwner() != &block)
      return failure("block argument not owned by block", block);
  }

  // Verify that this block has a terminator.
  if (block.empty()) {
    if (canBlockHaveNoTerminator(block))
      return false;
    return failure("block with no terminator", block);
  }

  // Verify the non-terminator instructions separately so that we can verify
  // they has no successors.
  for (auto &inst : llvm::make_range(block.begin(), std::prev(block.end()))) {
    if (inst.getNumSuccessors() != 0)
      return failure(
          "instruction with block successors must terminate its parent block",
          inst);

    if (verifyOperation(inst))
      return true;
  }

  // Verify the terminator.
  if (verifyOperation(block.back()))
    return true;
  if (block.back().isKnownNonTerminator() && !canBlockHaveNoTerminator(block))
    return failure("block with no terminator", block);

  // Verify that this block is not branching to a block of a different
  // region.
  for (Block *successor : block.getSuccessors())
    if (successor->getParent() != block.getParent())
      return failure("branching to block of a different region", block.back());

  return false;
}

/// Check the invariants of the specified operation.
bool FuncVerifier::verifyOperation(Instruction &op) {
  if (op.getFunction() != &fn)
    return failure("operation in the wrong function", op);

  // Check that operands are non-nil and structurally ok.
  for (auto *operand : op.getOperands()) {
    if (!operand)
      return failure("null operand found", op);

    if (operand->getFunction() != &fn)
      return failure("reference to operand defined in another function", op);
  }

  /// Verify that all of the attributes are okay.
  for (auto attr : op.getAttrs()) {
    if (!identifierRegex.match(attr.first))
      return failure("invalid attribute name '" + attr.first.strref() + "'",
                     op);
    if (verifyAttribute(attr.second, const_cast<Instruction &>(op)))
      return true;

    // Check for any optional dialect specific attributes.
    if (!attr.first.strref().contains('.'))
      continue;
    if (auto *dialect = getDialectForAttribute(attr, op))
      if (dialect->verifyInstructionAttribute(&op, attr))
        return true;
  }

  // If we can get operation info for this, check the custom hook.
  if (auto *opInfo = op.getAbstractOperation()) {
    if (opInfo->verifyInvariants(const_cast<Instruction *>(&op)))
      return true;
  }

  // Verify that all child blocks are ok.
  for (auto &region : op.getRegions())
    for (auto &b : region)
      if (verifyBlock(b, /*isTopLevel=*/false))
        return true;

  return false;
}

bool FuncVerifier::verifyDominance(Block &block) {
  // Verify the dominance of each of the held instructions.
  for (auto &inst : block)
    if (verifyInstDominance(inst))
      return true;
  return false;
}

bool FuncVerifier::verifyInstDominance(Instruction &inst) {
  // Check that operands properly dominate this use.
  for (unsigned operandNo = 0, e = inst.getNumOperands(); operandNo != e;
       ++operandNo) {
    auto *op = inst.getOperand(operandNo);
    if (domInfo->properlyDominates(op, &inst))
      continue;

    inst.emitError("operand #" + Twine(operandNo) +
                   " does not dominate this use");
    if (auto *useInst = op->getDefiningInst())
      useInst->emitNote("operand defined here");
    return true;
  }

  // Verify the dominance of each of the nested blocks within this instruction.
  for (auto &region : inst.getRegions())
    for (auto &block : region)
      if (verifyDominance(block))
        return true;

  return false;
}

//===----------------------------------------------------------------------===//
// Entrypoints
//===----------------------------------------------------------------------===//

/// Perform (potentially expensive) checks of invariants, used to detect
/// compiler bugs.  On error, this reports the error through the MLIRContext and
/// returns true.
bool Function::verify() { return FuncVerifier(*this).verify(); }

/// Perform (potentially expensive) checks of invariants, used to detect
/// compiler bugs.  On error, this reports the error through the MLIRContext and
/// returns true.
bool Module::verify() {

  /// Check that each function is correct.
  for (auto &fn : *this) {
    if (fn.verify())
      return true;
  }

  return false;
}