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| //===- llvm/MC/MCCodePadder.h - MC Code Padder ------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_MC_MCCODEPADDER_H
#define LLVM_MC_MCCODEPADDER_H
#include "MCFragment.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
namespace llvm {
class MCAsmLayout;
class MCCodePaddingPolicy;
class MCFragment;
class MCInst;
class MCObjectStreamer;
class MCSection;
typedef SmallVector<const MCPaddingFragment *, 8> MCPFRange;
struct MCCodePaddingContext {
bool IsPaddingActive;
bool IsBasicBlockReachableViaFallthrough;
bool IsBasicBlockReachableViaBranch;
};
/// Target-independent base class incharge of all code padding decisions for a
/// target. During encoding it determines if and where MCPaddingFragments will
/// be located, as later on, when layout information is available, it determines
/// their sizes.
class MCCodePadder {
MCCodePadder(const MCCodePadder &) = delete;
void operator=(const MCCodePadder &) = delete;
/// Determines if the MCCodePaddingPolicies are active.
bool ArePoliciesActive;
/// All the supported MCCodePaddingPolicies.
SmallPtrSet<MCCodePaddingPolicy *, 4> CodePaddingPolicies;
/// A pointer to the fragment of the instruction whose padding is currently
/// done for.
MCPaddingFragment *CurrHandledInstFragment;
/// A map holding the jurisdiction for each padding fragment. Key: padding
/// fragment. Value: The fragment's jurisdiction. A jurisdiction is a vector
/// of padding fragments whose conditions are being controlled by another
/// fragment, the key fragment.
DenseMap<MCPaddingFragment *, MCPFRange> FragmentToJurisdiction;
MCPFRange &getJurisdiction(MCPaddingFragment *Fragment, MCAsmLayout &Layout);
/// A map holding the maximal instruction window size relevant for a padding
/// fragment.
DenseMap<MCPaddingFragment *, uint64_t> FragmentToMaxWindowSize;
uint64_t getMaxWindowSize(MCPaddingFragment *Fragment, MCAsmLayout &Layout);
protected:
/// The current streamer, used to stream code padding.
MCObjectStreamer *OS;
bool addPolicy(MCCodePaddingPolicy *Policy);
virtual bool
basicBlockRequiresInsertionPoint(const MCCodePaddingContext &Context) {
return false;
}
virtual bool instructionRequiresInsertionPoint(const MCInst &Inst) {
return false;
}
virtual bool usePoliciesForBasicBlock(const MCCodePaddingContext &Context) {
return Context.IsPaddingActive;
}
public:
MCCodePadder()
: ArePoliciesActive(false), CurrHandledInstFragment(nullptr),
OS(nullptr) {}
virtual ~MCCodePadder();
/// Handles all target related code padding when starting to write a new
/// basic block to an object file.
///
/// \param OS The streamer used for writing the padding data and function.
/// \param Context the context of the padding, Embeds the basic block's
/// parameters.
void handleBasicBlockStart(MCObjectStreamer *OS,
const MCCodePaddingContext &Context);
/// Handles all target related code padding when done writing a block to an
/// object file.
///
/// \param Context the context of the padding, Embeds the basic block's
/// parameters.
void handleBasicBlockEnd(const MCCodePaddingContext &Context);
/// Handles all target related code padding before writing a new instruction
/// to an object file.
///
/// \param Inst the instruction.
void handleInstructionBegin(const MCInst &Inst);
/// Handles all target related code padding after writing an instruction to an
/// object file.
///
/// \param Inst the instruction.
void handleInstructionEnd(const MCInst &Inst);
/// Relaxes a fragment (changes the size of the padding) according to target
/// requirements. The new size computation is done w.r.t a layout.
///
/// \param Fragment The fragment to relax.
/// \param Layout Code layout information.
///
/// \returns true iff any relaxation occurred.
bool relaxFragment(MCPaddingFragment *Fragment, MCAsmLayout &Layout);
};
/// The base class for all padding policies, i.e. a rule or set of rules to pad
/// the generated code.
class MCCodePaddingPolicy {
MCCodePaddingPolicy() = delete;
MCCodePaddingPolicy(const MCCodePaddingPolicy &) = delete;
void operator=(const MCCodePaddingPolicy &) = delete;
protected:
/// A mask holding the kind of this policy, i.e. only the i'th bit will be set
/// where i is the kind number.
const uint64_t KindMask;
/// Instruction window size relevant to this policy.
const uint64_t WindowSize;
/// A boolean indicating which byte of the instruction determies its
/// instruction window. If true - the last byte of the instructions, o.w. -
/// the first byte of the instruction.
const bool InstByteIsLastByte;
MCCodePaddingPolicy(uint64_t Kind, uint64_t WindowSize,
bool InstByteIsLastByte)
: KindMask(UINT64_C(1) << Kind), WindowSize(WindowSize),
InstByteIsLastByte(InstByteIsLastByte) {}
/// Computes and returns the offset of the consecutive fragment of a given
/// fragment.
///
/// \param Fragment The fragment whose consecutive offset will be computed.
/// \param Layout Code layout information.
///
/// \returns the offset of the consecutive fragment of \p Fragment.
static uint64_t getNextFragmentOffset(const MCFragment *Fragment,
const MCAsmLayout &Layout);
/// Returns the instruction byte of an instruction pointed by a given
/// MCPaddingFragment. An instruction byte is the address of the byte of an
/// instruction which determines its instruction window.
///
/// \param Fragment The fragment pointing to the instruction.
/// \param Layout Code layout information.
///
/// \returns the instruction byte of an instruction pointed by \p Fragment.
uint64_t getFragmentInstByte(const MCPaddingFragment *Fragment,
MCAsmLayout &Layout) const;
uint64_t computeWindowEndAddress(const MCPaddingFragment *Fragment,
uint64_t Offset, MCAsmLayout &Layout) const;
/// Computes and returns the penalty weight of a first instruction window in a
/// range. This requires a special function since the first window does not
/// contain all the padding fragments in that window. It only contains all the
/// padding fragments starting from the relevant insertion point.
///
/// \param Window The first window.
/// \param Offset The offset of the parent section relative to the beginning
/// of the file, mod the window size.
/// \param Layout Code layout information.
///
/// \returns the penalty weight of a first instruction window in a range, \p
/// Window.
double computeFirstWindowPenaltyWeight(const MCPFRange &Window,
uint64_t Offset,
MCAsmLayout &Layout) const;
/// Computes and returns the penalty caused by an instruction window.
///
/// \param Window The instruction window.
/// \param Offset The offset of the parent section relative to the beginning
/// of the file, mod the window size.
/// \param Layout Code layout information.
///
/// \returns the penalty caused by \p Window.
virtual double computeWindowPenaltyWeight(const MCPFRange &Window,
uint64_t Offset,
MCAsmLayout &Layout) const = 0;
public:
virtual ~MCCodePaddingPolicy() {}
/// Returns the kind mask of this policy - A mask holding the kind of this
/// policy, i.e. only the i'th bit will be set where i is the kind number.
uint64_t getKindMask() const { return KindMask; }
/// Returns the instruction window size relevant to this policy.
uint64_t getWindowSize() const { return WindowSize; }
/// Returns true if the last byte of an instruction determines its instruction
/// window, or false if the first of an instruction determines it.
bool isInstByteLastByte() const { return InstByteIsLastByte; }
/// Returns true iff this policy needs padding for a given basic block.
///
/// \param Context the context of the padding, Embeds the basic block's
/// parameters.
///
/// \returns true iff this policy needs padding for the basic block.
virtual bool
basicBlockRequiresPaddingFragment(const MCCodePaddingContext &Context) const {
return false;
}
/// Returns true iff this policy needs padding for a given instruction.
///
/// \param Inst The given instruction.
///
/// \returns true iff this policy needs padding for \p Inst.
virtual bool instructionRequiresPaddingFragment(const MCInst &Inst) const {
return false;
}
/// Computes and returns the penalty caused by a range of instruction windows.
/// The weight is computed for each window separelty and then accumulated.
///
/// \param Range The range.
/// \param Offset The offset of the parent section relative to the beginning
/// of the file, mod the window size.
/// \param Layout Code layout information.
///
/// \returns the penalty caused by \p Range.
double computeRangePenaltyWeight(const MCPFRange &Range, uint64_t Offset,
MCAsmLayout &Layout) const;
};
} // namespace llvm
#endif // LLVM_MC_MCCODEPADDER_H
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