CodeMetrics.h

Go to the documentation of this file.

//===- CodeMetrics.h - Code cost measurements -------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements various weight measurements for code, helping
// the Inliner and other passes decide whether to duplicate its contents.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_CODEMETRICS_H
#define LLVM_ANALYSIS_CODEMETRICS_H

#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/IR/CallSite.h"

namespace llvm {
class AssumptionTracker;
class BasicBlock;
class Loop;
class Function;
class Instruction;
class DataLayout;
class TargetTransformInfo;
class Value;

/// \brief Check whether a call will lower to something small.
///
/// This tests checks whether this callsite will lower to something
/// significantly cheaper than a traditional call, often a single
/// instruction. Note that if isInstructionFree(CS.getInstruction()) would
/// return true, so will this function.
bool callIsSmall(ImmutableCallSite CS);

/// \brief Utility to calculate the size and a few similar metrics for a set
/// of basic blocks.
struct CodeMetrics {
  /// \brief True if this function contains a call to setjmp or other functions
  /// with attribute "returns twice" without having the attribute itself.
  bool exposesReturnsTwice;

  /// \brief True if this function calls itself.
  bool isRecursive;

  /// \brief True if this function cannot be duplicated.
  ///
  /// True if this function contains one or more indirect branches, or it contains
  /// one or more 'noduplicate' instructions.
  bool notDuplicatable;

  /// \brief True if this function calls alloca (in the C sense).
  bool usesDynamicAlloca;

  /// \brief Number of instructions in the analyzed blocks.
  unsigned NumInsts;

  /// \brief Number of analyzed blocks.
  unsigned NumBlocks;

  /// \brief Keeps track of basic block code size estimates.
  DenseMap<const BasicBlock *, unsigned> NumBBInsts;

  /// \brief Keep track of the number of calls to 'big' functions.
  unsigned NumCalls;

  /// \brief The number of calls to internal functions with a single caller.
  ///
  /// These are likely targets for future inlining, likely exposed by
  /// interleaved devirtualization.
  unsigned NumInlineCandidates;

  /// \brief How many instructions produce vector values.
  ///
  /// The inliner is more aggressive with inlining vector kernels.
  unsigned NumVectorInsts;

  /// \brief How many 'ret' instructions the blocks contain.
  unsigned NumRets;

  CodeMetrics()
      : exposesReturnsTwice(false), isRecursive(false), notDuplicatable(false),
        usesDynamicAlloca(false), NumInsts(0), NumBlocks(0), NumCalls(0),
        NumInlineCandidates(0), NumVectorInsts(0), NumRets(0) {}

  /// \brief Add information about a block to the current state.
  void analyzeBasicBlock(const BasicBlock *BB, const TargetTransformInfo &TTI,
                         SmallPtrSetImpl<const Value*> &EphValues);

  /// \brief Collect a loop's ephemeral values (those used only by an assume
  /// or similar intrinsics in the loop).
  static void collectEphemeralValues(const Loop *L, AssumptionTracker *AT,
                                     SmallPtrSetImpl<const Value*> &EphValues);

  /// \brief Collect a functions's ephemeral values (those used only by an
  /// assume or similar intrinsics in the function).
  static void collectEphemeralValues(const Function *L, AssumptionTracker *AT,
                                     SmallPtrSetImpl<const Value*> &EphValues);
};

}

#endif