InlineCost.h   [plain text]

//===- InlineCost.h - Cost analysis for inliner -----------------*- 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 heuristics for inlining decisions.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_INLINECOST_H
#define LLVM_ANALYSIS_INLINECOST_H

#include "llvm/Function.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/ValueMap.h"
#include "llvm/Analysis/CodeMetrics.h"
#include <cassert>
#include <climits>
#include <vector>

namespace llvm {

  class CallSite;
  class TargetData;

  namespace InlineConstants {
    // Various magic constants used to adjust heuristics.
    const int InstrCost = 5;
    const int IndirectCallThreshold = 100;
    const int CallPenalty = 25;
    const int LastCallToStaticBonus = -15000;
    const int ColdccPenalty = 2000;
    const int NoreturnPenalty = 10000;
    /// Do not inline functions which allocate this many bytes on the stack
    /// when the caller is recursive.
    const unsigned TotalAllocaSizeRecursiveCaller = 1024;
  }

  /// \brief Represents the cost of inlining a function.
  ///
  /// This supports special values for functions which should "always" or
  /// "never" be inlined. Otherwise, the cost represents a unitless amount;
  /// smaller values increase the likelihood of the function being inlined.
  ///
  /// Objects of this type also provide the adjusted threshold for inlining
  /// based on the information available for a particular callsite. They can be
  /// directly tested to determine if inlining should occur given the cost and
  /// threshold for this cost metric.
  class InlineCost {
    enum SentinelValues {
      AlwaysInlineCost = INT_MIN,
      NeverInlineCost = INT_MAX
    };

    /// \brief The estimated cost of inlining this callsite.
    const int Cost;

    /// \brief The adjusted threshold against which this cost was computed.
    const int Threshold;

    // Trivial constructor, interesting logic in the factory functions below.
    InlineCost(int Cost, int Threshold)
      : Cost(Cost), Threshold(Threshold) {}

  public:
    static InlineCost get(int Cost, int Threshold) {
      assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
      assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
      return InlineCost(Cost, Threshold);
    }
    static InlineCost getAlways() {
      return InlineCost(AlwaysInlineCost, 0);
    }
    static InlineCost getNever() {
      return InlineCost(NeverInlineCost, 0);
    }

    /// \brief Test whether the inline cost is low enough for inlining.
    operator bool() const {
      return Cost < Threshold;
    }

    bool isAlways() const   { return Cost == AlwaysInlineCost; }
    bool isNever() const    { return Cost == NeverInlineCost; }
    bool isVariable() const { return !isAlways() && !isNever(); }

    /// \brief Get the inline cost estimate.
    /// It is an error to call this on an "always" or "never" InlineCost.
    int getCost() const {
      assert(isVariable() && "Invalid access of InlineCost");
      return Cost;
    }

    /// \brief Get the cost delta from the threshold for inlining.
    /// Only valid if the cost is of the variable kind. Returns a negative
    /// value if the cost is too high to inline.
    int getCostDelta() const { return Threshold - getCost(); }
  };

  /// InlineCostAnalyzer - Cost analyzer used by inliner.
  class InlineCostAnalyzer {
    // TargetData if available, or null.
    const TargetData *TD;

  public:
    InlineCostAnalyzer(): TD(0) {}

    void setTargetData(const TargetData *TData) { TD = TData; }

    /// \brief Get an InlineCost object representing the cost of inlining this
    /// callsite.
    ///
    /// Note that threshold is passed into this function. Only costs below the
    /// threshold are computed with any accuracy. The threshold can be used to
    /// bound the computation necessary to determine whether the cost is
    /// sufficiently low to warrant inlining.
    InlineCost getInlineCost(CallSite CS, int Threshold);
    /// getCalledFunction - The heuristic used to determine if we should inline
    /// the function call or not.  The callee is explicitly specified, to allow
    /// you to calculate the cost of inlining a function via a pointer.  This
    /// behaves exactly as the version with no explicit callee parameter in all
    /// other respects.
    //
    //  Note: This is used by out-of-tree passes, please do not remove without
    //  adding a replacement API.
    InlineCost getInlineCost(CallSite CS, Function *Callee, int Threshold);
  };
}

#endif