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371 lines
15 KiB
C++
371 lines
15 KiB
C++
//===- MCCodePadder.cpp - Target MC Code Padder ---------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/MC/MCAsmLayout.h"
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#include "llvm/MC/MCCodePadder.h"
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#include "llvm/MC/MCObjectStreamer.h"
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#include <algorithm>
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#include <limits>
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#include <numeric>
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using namespace llvm;
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//---------------------------------------------------------------------------
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// MCCodePadder
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//
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MCCodePadder::~MCCodePadder() {
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for (auto *Policy : CodePaddingPolicies)
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delete Policy;
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}
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bool MCCodePadder::addPolicy(MCCodePaddingPolicy *Policy) {
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assert(Policy && "Policy must be valid");
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return CodePaddingPolicies.insert(Policy).second;
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}
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void MCCodePadder::handleBasicBlockStart(MCObjectStreamer *OS,
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const MCCodePaddingContext &Context) {
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assert(OS != nullptr && "OS must be valid");
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assert(this->OS == nullptr && "Still handling another basic block");
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this->OS = OS;
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ArePoliciesActive = usePoliciesForBasicBlock(Context);
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bool InsertionPoint = basicBlockRequiresInsertionPoint(Context);
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assert((!InsertionPoint ||
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OS->getCurrentFragment()->getKind() != MCFragment::FT_Align) &&
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"Cannot insert padding nops right after an alignment fragment as it "
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"will ruin the alignment");
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uint64_t PoliciesMask = MCPaddingFragment::PFK_None;
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if (ArePoliciesActive) {
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PoliciesMask = std::accumulate(
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CodePaddingPolicies.begin(), CodePaddingPolicies.end(),
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MCPaddingFragment::PFK_None,
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[&Context](uint64_t Mask,
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const MCCodePaddingPolicy *Policy) -> uint64_t {
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return Policy->basicBlockRequiresPaddingFragment(Context)
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? (Mask | Policy->getKindMask())
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: Mask;
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});
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}
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if (InsertionPoint || PoliciesMask != MCPaddingFragment::PFK_None) {
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MCPaddingFragment *PaddingFragment = OS->getOrCreatePaddingFragment();
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if (InsertionPoint)
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PaddingFragment->setAsInsertionPoint();
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PaddingFragment->setPaddingPoliciesMask(
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PaddingFragment->getPaddingPoliciesMask() | PoliciesMask);
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}
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}
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void MCCodePadder::handleBasicBlockEnd(const MCCodePaddingContext &Context) {
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assert(this->OS != nullptr && "Not handling a basic block");
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OS = nullptr;
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}
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void MCCodePadder::handleInstructionBegin(const MCInst &Inst) {
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if (!OS)
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return; // instruction was emitted outside a function
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assert(CurrHandledInstFragment == nullptr && "Can't start handling an "
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"instruction while still "
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"handling another instruction");
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bool InsertionPoint = instructionRequiresInsertionPoint(Inst);
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assert((!InsertionPoint ||
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OS->getCurrentFragment()->getKind() != MCFragment::FT_Align) &&
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"Cannot insert padding nops right after an alignment fragment as it "
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"will ruin the alignment");
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uint64_t PoliciesMask = MCPaddingFragment::PFK_None;
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if (ArePoliciesActive) {
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PoliciesMask = std::accumulate(
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CodePaddingPolicies.begin(), CodePaddingPolicies.end(),
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MCPaddingFragment::PFK_None,
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[&Inst](uint64_t Mask, const MCCodePaddingPolicy *Policy) -> uint64_t {
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return Policy->instructionRequiresPaddingFragment(Inst)
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? (Mask | Policy->getKindMask())
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: Mask;
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});
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}
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MCFragment *CurrFragment = OS->getCurrentFragment();
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// CurrFragment can be a previously created MCPaddingFragment. If so, let's
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// update it with the information we have, such as the instruction that it
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// should point to.
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bool needToUpdateCurrFragment =
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CurrFragment != nullptr &&
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CurrFragment->getKind() == MCFragment::FT_Padding;
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if (InsertionPoint || PoliciesMask != MCPaddingFragment::PFK_None ||
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needToUpdateCurrFragment) {
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// temporarily holding the fragment as CurrHandledInstFragment, to be
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// updated after the instruction will be written
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CurrHandledInstFragment = OS->getOrCreatePaddingFragment();
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if (InsertionPoint)
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CurrHandledInstFragment->setAsInsertionPoint();
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CurrHandledInstFragment->setPaddingPoliciesMask(
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CurrHandledInstFragment->getPaddingPoliciesMask() | PoliciesMask);
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}
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}
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void MCCodePadder::handleInstructionEnd(const MCInst &Inst) {
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if (!OS)
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return; // instruction was emitted outside a function
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if (CurrHandledInstFragment == nullptr)
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return;
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MCFragment *InstFragment = OS->getCurrentFragment();
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if (MCDataFragment *InstDataFragment =
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dyn_cast_or_null<MCDataFragment>(InstFragment))
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// Inst is a fixed size instruction and was encoded into a MCDataFragment.
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// Let the fragment hold it and its size. Its size is the current size of
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// the data fragment, as the padding fragment was inserted right before it
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// and nothing was written yet except Inst
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CurrHandledInstFragment->setInstAndInstSize(
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Inst, InstDataFragment->getContents().size());
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else if (MCRelaxableFragment *InstRelaxableFragment =
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dyn_cast_or_null<MCRelaxableFragment>(InstFragment))
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// Inst may be relaxed and its size may vary.
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// Let the fragment hold the instruction and the MCRelaxableFragment
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// that's holding it.
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CurrHandledInstFragment->setInstAndInstFragment(Inst,
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InstRelaxableFragment);
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else
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llvm_unreachable("After encoding an instruction current fragment must be "
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"either a MCDataFragment or a MCRelaxableFragment");
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CurrHandledInstFragment = nullptr;
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}
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MCPFRange &MCCodePadder::getJurisdiction(MCPaddingFragment *Fragment,
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MCAsmLayout &Layout) {
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auto JurisdictionLocation = FragmentToJurisdiction.find(Fragment);
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if (JurisdictionLocation != FragmentToJurisdiction.end())
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return JurisdictionLocation->second;
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MCPFRange Jurisdiction;
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// Forward scanning the fragments in this section, starting from the given
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// fragments, and adding relevant MCPaddingFragments to the Jurisdiction
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for (MCFragment *CurrFragment = Fragment; CurrFragment != nullptr;
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CurrFragment = CurrFragment->getNextNode()) {
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MCPaddingFragment *CurrPaddingFragment =
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dyn_cast<MCPaddingFragment>(CurrFragment);
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if (CurrPaddingFragment == nullptr)
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continue;
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if (CurrPaddingFragment != Fragment &&
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CurrPaddingFragment->isInsertionPoint())
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// Found next insertion point Fragment. From now on it's its jurisdiction.
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break;
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for (const auto *Policy : CodePaddingPolicies) {
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if (CurrPaddingFragment->hasPaddingPolicy(Policy->getKindMask())) {
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Jurisdiction.push_back(CurrPaddingFragment);
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break;
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}
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}
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}
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auto InsertionResult =
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FragmentToJurisdiction.insert(std::make_pair(Fragment, Jurisdiction));
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assert(InsertionResult.second &&
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"Insertion to FragmentToJurisdiction failed");
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return InsertionResult.first->second;
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}
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uint64_t MCCodePadder::getMaxWindowSize(MCPaddingFragment *Fragment,
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MCAsmLayout &Layout) {
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auto MaxFragmentSizeLocation = FragmentToMaxWindowSize.find(Fragment);
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if (MaxFragmentSizeLocation != FragmentToMaxWindowSize.end())
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return MaxFragmentSizeLocation->second;
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MCPFRange &Jurisdiction = getJurisdiction(Fragment, Layout);
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uint64_t JurisdictionMask = MCPaddingFragment::PFK_None;
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for (const auto *Protege : Jurisdiction)
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JurisdictionMask |= Protege->getPaddingPoliciesMask();
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uint64_t MaxFragmentSize = UINT64_C(0);
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for (const auto *Policy : CodePaddingPolicies)
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if ((JurisdictionMask & Policy->getKindMask()) !=
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MCPaddingFragment::PFK_None)
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MaxFragmentSize = std::max(MaxFragmentSize, Policy->getWindowSize());
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auto InsertionResult =
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FragmentToMaxWindowSize.insert(std::make_pair(Fragment, MaxFragmentSize));
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assert(InsertionResult.second &&
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"Insertion to FragmentToMaxWindowSize failed");
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return InsertionResult.first->second;
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}
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bool MCCodePadder::relaxFragment(MCPaddingFragment *Fragment,
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MCAsmLayout &Layout) {
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if (!Fragment->isInsertionPoint())
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return false;
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uint64_t OldSize = Fragment->getSize();
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uint64_t MaxWindowSize = getMaxWindowSize(Fragment, Layout);
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if (MaxWindowSize == UINT64_C(0))
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return false;
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assert(isPowerOf2_64(MaxWindowSize) &&
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"MaxWindowSize must be an integer power of 2");
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uint64_t SectionAlignment = Fragment->getParent()->getAlignment();
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assert(isPowerOf2_64(SectionAlignment) &&
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"SectionAlignment must be an integer power of 2");
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MCPFRange &Jurisdiction = getJurisdiction(Fragment, Layout);
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uint64_t OptimalSize = UINT64_C(0);
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double OptimalWeight = std::numeric_limits<double>::max();
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uint64_t MaxFragmentSize = MaxWindowSize - UINT16_C(1);
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for (uint64_t Size = UINT64_C(0); Size <= MaxFragmentSize; ++Size) {
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Fragment->setSize(Size);
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Layout.invalidateFragmentsFrom(Fragment);
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double SizeWeight = 0.0;
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// The section is guaranteed to be aligned to SectionAlignment, but that
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// doesn't guarantee the exact section offset w.r.t. the policies window
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// size.
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// As a concrete example, the section could be aligned to 16B, but a
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// policy's window size can be 32B. That means that the section actual start
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// address can either be 0mod32 or 16mod32. The said policy will act
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// differently for each case, so we need to take both into consideration.
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for (uint64_t Offset = UINT64_C(0); Offset < MaxWindowSize;
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Offset += SectionAlignment) {
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double OffsetWeight = std::accumulate(
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CodePaddingPolicies.begin(), CodePaddingPolicies.end(), 0.0,
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[&Jurisdiction, &Offset, &Layout](
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double Weight, const MCCodePaddingPolicy *Policy) -> double {
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double PolicyWeight =
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Policy->computeRangePenaltyWeight(Jurisdiction, Offset, Layout);
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assert(PolicyWeight >= 0.0 && "A penalty weight must be positive");
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return Weight + PolicyWeight;
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});
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SizeWeight = std::max(SizeWeight, OffsetWeight);
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}
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if (SizeWeight < OptimalWeight) {
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OptimalWeight = SizeWeight;
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OptimalSize = Size;
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}
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if (OptimalWeight == 0.0)
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break;
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}
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Fragment->setSize(OptimalSize);
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Layout.invalidateFragmentsFrom(Fragment);
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return OldSize != OptimalSize;
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}
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//---------------------------------------------------------------------------
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// MCCodePaddingPolicy
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//
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uint64_t MCCodePaddingPolicy::getNextFragmentOffset(const MCFragment *Fragment,
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const MCAsmLayout &Layout) {
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assert(Fragment != nullptr && "Fragment cannot be null");
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MCFragment const *NextFragment = Fragment->getNextNode();
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return NextFragment == nullptr
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? Layout.getSectionAddressSize(Fragment->getParent())
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: Layout.getFragmentOffset(NextFragment);
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}
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uint64_t
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MCCodePaddingPolicy::getFragmentInstByte(const MCPaddingFragment *Fragment,
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MCAsmLayout &Layout) const {
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uint64_t InstByte = getNextFragmentOffset(Fragment, Layout);
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if (InstByteIsLastByte)
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InstByte += Fragment->getInstSize() - UINT64_C(1);
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return InstByte;
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}
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uint64_t
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MCCodePaddingPolicy::computeWindowEndAddress(const MCPaddingFragment *Fragment,
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uint64_t Offset,
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MCAsmLayout &Layout) const {
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uint64_t InstByte = getFragmentInstByte(Fragment, Layout);
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return alignTo(InstByte + UINT64_C(1) + Offset, WindowSize) - Offset;
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}
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double MCCodePaddingPolicy::computeRangePenaltyWeight(
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const MCPFRange &Range, uint64_t Offset, MCAsmLayout &Layout) const {
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SmallVector<MCPFRange, 8> Windows;
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SmallVector<MCPFRange, 8>::iterator CurrWindowLocation = Windows.end();
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for (const MCPaddingFragment *Fragment : Range) {
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if (!Fragment->hasPaddingPolicy(getKindMask()))
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continue;
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uint64_t FragmentWindowEndAddress =
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computeWindowEndAddress(Fragment, Offset, Layout);
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if (CurrWindowLocation == Windows.end() ||
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FragmentWindowEndAddress !=
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computeWindowEndAddress(*CurrWindowLocation->begin(), Offset,
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Layout)) {
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// next window is starting
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Windows.push_back(MCPFRange());
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CurrWindowLocation = Windows.end() - 1;
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}
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CurrWindowLocation->push_back(Fragment);
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}
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if (Windows.empty())
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return 0.0;
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double RangeWeight = 0.0;
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SmallVector<MCPFRange, 8>::iterator I = Windows.begin();
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RangeWeight += computeFirstWindowPenaltyWeight(*I, Offset, Layout);
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++I;
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RangeWeight += std::accumulate(
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I, Windows.end(), 0.0,
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[this, &Layout, &Offset](double Weight, MCPFRange &Window) -> double {
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return Weight += computeWindowPenaltyWeight(Window, Offset, Layout);
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});
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return RangeWeight;
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}
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double MCCodePaddingPolicy::computeFirstWindowPenaltyWeight(
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const MCPFRange &Window, uint64_t Offset, MCAsmLayout &Layout) const {
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if (Window.empty())
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return 0.0;
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uint64_t WindowEndAddress =
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computeWindowEndAddress(*Window.begin(), Offset, Layout);
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MCPFRange FullWindowFirstPart; // will hold all the fragments that are in the
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// same window as the fragments in the given
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// window but their penalty weight should not
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// be added
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for (const MCFragment *Fragment = (*Window.begin())->getPrevNode();
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Fragment != nullptr; Fragment = Fragment->getPrevNode()) {
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const MCPaddingFragment *PaddingNopFragment =
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dyn_cast<MCPaddingFragment>(Fragment);
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if (PaddingNopFragment == nullptr ||
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!PaddingNopFragment->hasPaddingPolicy(getKindMask()))
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continue;
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if (WindowEndAddress !=
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computeWindowEndAddress(PaddingNopFragment, Offset, Layout))
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break;
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FullWindowFirstPart.push_back(PaddingNopFragment);
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}
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std::reverse(FullWindowFirstPart.begin(), FullWindowFirstPart.end());
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double FullWindowFirstPartWeight =
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computeWindowPenaltyWeight(FullWindowFirstPart, Offset, Layout);
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MCPFRange FullWindow(
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FullWindowFirstPart); // will hold all the fragments that are in the
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// same window as the fragments in the given
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// window, whether their weight should be added
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// or not
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FullWindow.append(Window.begin(), Window.end());
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double FullWindowWeight =
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computeWindowPenaltyWeight(FullWindow, Offset, Layout);
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assert(FullWindowWeight >= FullWindowFirstPartWeight &&
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"More fragments necessarily means bigger weight");
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return FullWindowWeight - FullWindowFirstPartWeight;
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}
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