437 lines
15 KiB
C++
437 lines
15 KiB
C++
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//===- PtrState.cpp -------------------------------------------------------===//
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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 "PtrState.h"
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#include "DependencyAnalysis.h"
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#include "ObjCARC.h"
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#include "llvm/Analysis/ObjCARCAnalysisUtils.h"
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#include "llvm/Analysis/ObjCARCInstKind.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Value.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include <cassert>
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#include <iterator>
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#include <utility>
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using namespace llvm;
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using namespace llvm::objcarc;
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#define DEBUG_TYPE "objc-arc-ptr-state"
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//===----------------------------------------------------------------------===//
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// Utility
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//===----------------------------------------------------------------------===//
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raw_ostream &llvm::objcarc::operator<<(raw_ostream &OS, const Sequence S) {
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switch (S) {
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case S_None:
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return OS << "S_None";
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case S_Retain:
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return OS << "S_Retain";
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case S_CanRelease:
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return OS << "S_CanRelease";
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case S_Use:
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return OS << "S_Use";
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case S_Release:
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return OS << "S_Release";
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case S_MovableRelease:
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return OS << "S_MovableRelease";
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case S_Stop:
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return OS << "S_Stop";
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}
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llvm_unreachable("Unknown sequence type.");
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}
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//===----------------------------------------------------------------------===//
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// Sequence
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//===----------------------------------------------------------------------===//
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static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) {
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// The easy cases.
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if (A == B)
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return A;
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if (A == S_None || B == S_None)
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return S_None;
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if (A > B)
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std::swap(A, B);
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if (TopDown) {
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// Choose the side which is further along in the sequence.
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if ((A == S_Retain || A == S_CanRelease) &&
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(B == S_CanRelease || B == S_Use))
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return B;
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} else {
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// Choose the side which is further along in the sequence.
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if ((A == S_Use || A == S_CanRelease) &&
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(B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease))
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return A;
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// If both sides are releases, choose the more conservative one.
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if (A == S_Stop && (B == S_Release || B == S_MovableRelease))
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return A;
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if (A == S_Release && B == S_MovableRelease)
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return A;
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}
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return S_None;
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}
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//===----------------------------------------------------------------------===//
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// RRInfo
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//===----------------------------------------------------------------------===//
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void RRInfo::clear() {
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KnownSafe = false;
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IsTailCallRelease = false;
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ReleaseMetadata = nullptr;
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Calls.clear();
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ReverseInsertPts.clear();
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CFGHazardAfflicted = false;
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}
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bool RRInfo::Merge(const RRInfo &Other) {
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// Conservatively merge the ReleaseMetadata information.
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if (ReleaseMetadata != Other.ReleaseMetadata)
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ReleaseMetadata = nullptr;
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// Conservatively merge the boolean state.
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KnownSafe &= Other.KnownSafe;
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IsTailCallRelease &= Other.IsTailCallRelease;
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CFGHazardAfflicted |= Other.CFGHazardAfflicted;
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// Merge the call sets.
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Calls.insert(Other.Calls.begin(), Other.Calls.end());
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// Merge the insert point sets. If there are any differences,
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// that makes this a partial merge.
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bool Partial = ReverseInsertPts.size() != Other.ReverseInsertPts.size();
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for (Instruction *Inst : Other.ReverseInsertPts)
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Partial |= ReverseInsertPts.insert(Inst).second;
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return Partial;
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}
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//===----------------------------------------------------------------------===//
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// PtrState
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//===----------------------------------------------------------------------===//
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void PtrState::SetKnownPositiveRefCount() {
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LLVM_DEBUG(dbgs() << " Setting Known Positive.\n");
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KnownPositiveRefCount = true;
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}
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void PtrState::ClearKnownPositiveRefCount() {
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LLVM_DEBUG(dbgs() << " Clearing Known Positive.\n");
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KnownPositiveRefCount = false;
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}
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void PtrState::SetSeq(Sequence NewSeq) {
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LLVM_DEBUG(dbgs() << " Old: " << GetSeq() << "; New: " << NewSeq
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<< "\n");
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Seq = NewSeq;
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}
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void PtrState::ResetSequenceProgress(Sequence NewSeq) {
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LLVM_DEBUG(dbgs() << " Resetting sequence progress.\n");
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SetSeq(NewSeq);
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Partial = false;
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RRI.clear();
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}
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void PtrState::Merge(const PtrState &Other, bool TopDown) {
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Seq = MergeSeqs(GetSeq(), Other.GetSeq(), TopDown);
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KnownPositiveRefCount &= Other.KnownPositiveRefCount;
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// If we're not in a sequence (anymore), drop all associated state.
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if (Seq == S_None) {
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Partial = false;
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RRI.clear();
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} else if (Partial || Other.Partial) {
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// If we're doing a merge on a path that's previously seen a partial
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// merge, conservatively drop the sequence, to avoid doing partial
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// RR elimination. If the branch predicates for the two merge differ,
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// mixing them is unsafe.
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ClearSequenceProgress();
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} else {
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// Otherwise merge the other PtrState's RRInfo into our RRInfo. At this
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// point, we know that currently we are not partial. Stash whether or not
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// the merge operation caused us to undergo a partial merging of reverse
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// insertion points.
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Partial = RRI.Merge(Other.RRI);
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}
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}
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//===----------------------------------------------------------------------===//
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// BottomUpPtrState
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//===----------------------------------------------------------------------===//
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bool BottomUpPtrState::InitBottomUp(ARCMDKindCache &Cache, Instruction *I) {
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// If we see two releases in a row on the same pointer. If so, make
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// a note, and we'll cicle back to revisit it after we've
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// hopefully eliminated the second release, which may allow us to
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// eliminate the first release too.
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// Theoretically we could implement removal of nested retain+release
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// pairs by making PtrState hold a stack of states, but this is
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// simple and avoids adding overhead for the non-nested case.
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bool NestingDetected = false;
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if (GetSeq() == S_Release || GetSeq() == S_MovableRelease) {
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LLVM_DEBUG(
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dbgs() << " Found nested releases (i.e. a release pair)\n");
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NestingDetected = true;
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}
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MDNode *ReleaseMetadata =
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I->getMetadata(Cache.get(ARCMDKindID::ImpreciseRelease));
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Sequence NewSeq = ReleaseMetadata ? S_MovableRelease : S_Release;
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ResetSequenceProgress(NewSeq);
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SetReleaseMetadata(ReleaseMetadata);
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SetKnownSafe(HasKnownPositiveRefCount());
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SetTailCallRelease(cast<CallInst>(I)->isTailCall());
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InsertCall(I);
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SetKnownPositiveRefCount();
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return NestingDetected;
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}
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bool BottomUpPtrState::MatchWithRetain() {
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SetKnownPositiveRefCount();
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Sequence OldSeq = GetSeq();
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switch (OldSeq) {
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case S_Stop:
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case S_Release:
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case S_MovableRelease:
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case S_Use:
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// If OldSeq is not S_Use or OldSeq is S_Use and we are tracking an
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// imprecise release, clear our reverse insertion points.
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if (OldSeq != S_Use || IsTrackingImpreciseReleases())
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ClearReverseInsertPts();
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LLVM_FALLTHROUGH;
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case S_CanRelease:
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return true;
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case S_None:
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return false;
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case S_Retain:
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llvm_unreachable("bottom-up pointer in retain state!");
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}
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llvm_unreachable("Sequence unknown enum value");
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}
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bool BottomUpPtrState::HandlePotentialAlterRefCount(Instruction *Inst,
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const Value *Ptr,
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ProvenanceAnalysis &PA,
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ARCInstKind Class) {
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Sequence S = GetSeq();
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// Check for possible releases.
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if (!CanDecrementRefCount(Inst, Ptr, PA, Class))
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return false;
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LLVM_DEBUG(dbgs() << " CanAlterRefCount: Seq: " << S << "; "
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<< *Ptr << "\n");
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switch (S) {
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case S_Use:
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SetSeq(S_CanRelease);
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return true;
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case S_CanRelease:
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case S_Release:
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case S_MovableRelease:
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case S_Stop:
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case S_None:
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return false;
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case S_Retain:
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llvm_unreachable("bottom-up pointer in retain state!");
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}
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llvm_unreachable("Sequence unknown enum value");
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}
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void BottomUpPtrState::HandlePotentialUse(BasicBlock *BB, Instruction *Inst,
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const Value *Ptr,
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ProvenanceAnalysis &PA,
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ARCInstKind Class) {
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auto SetSeqAndInsertReverseInsertPt = [&](Sequence NewSeq){
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assert(!HasReverseInsertPts());
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SetSeq(NewSeq);
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// If this is an invoke instruction, we're scanning it as part of
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// one of its successor blocks, since we can't insert code after it
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// in its own block, and we don't want to split critical edges.
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BasicBlock::iterator InsertAfter;
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if (isa<InvokeInst>(Inst)) {
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const auto IP = BB->getFirstInsertionPt();
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InsertAfter = IP == BB->end() ? std::prev(BB->end()) : IP;
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if (isa<CatchSwitchInst>(InsertAfter))
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// A catchswitch must be the only non-phi instruction in its basic
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// block, so attempting to insert an instruction into such a block would
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// produce invalid IR.
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SetCFGHazardAfflicted(true);
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} else {
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InsertAfter = std::next(Inst->getIterator());
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}
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if (InsertAfter != BB->end())
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InsertAfter = skipDebugIntrinsics(InsertAfter);
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InsertReverseInsertPt(&*InsertAfter);
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};
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// Check for possible direct uses.
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switch (GetSeq()) {
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case S_Release:
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case S_MovableRelease:
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if (CanUse(Inst, Ptr, PA, Class)) {
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LLVM_DEBUG(dbgs() << " CanUse: Seq: " << GetSeq() << "; "
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<< *Ptr << "\n");
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SetSeqAndInsertReverseInsertPt(S_Use);
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} else if (Seq == S_Release && IsUser(Class)) {
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LLVM_DEBUG(dbgs() << " PreciseReleaseUse: Seq: " << GetSeq()
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<< "; " << *Ptr << "\n");
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// Non-movable releases depend on any possible objc pointer use.
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SetSeqAndInsertReverseInsertPt(S_Stop);
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} else if (const auto *Call = getreturnRVOperand(*Inst, Class)) {
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if (CanUse(Call, Ptr, PA, GetBasicARCInstKind(Call))) {
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LLVM_DEBUG(dbgs() << " ReleaseUse: Seq: " << GetSeq() << "; "
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<< *Ptr << "\n");
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SetSeqAndInsertReverseInsertPt(S_Stop);
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}
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}
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break;
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case S_Stop:
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if (CanUse(Inst, Ptr, PA, Class)) {
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LLVM_DEBUG(dbgs() << " PreciseStopUse: Seq: " << GetSeq()
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<< "; " << *Ptr << "\n");
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SetSeq(S_Use);
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}
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break;
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case S_CanRelease:
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case S_Use:
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case S_None:
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break;
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case S_Retain:
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llvm_unreachable("bottom-up pointer in retain state!");
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}
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}
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//===----------------------------------------------------------------------===//
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// TopDownPtrState
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//===----------------------------------------------------------------------===//
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bool TopDownPtrState::InitTopDown(ARCInstKind Kind, Instruction *I) {
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bool NestingDetected = false;
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// Don't do retain+release tracking for ARCInstKind::RetainRV, because
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// it's
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// better to let it remain as the first instruction after a call.
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if (Kind != ARCInstKind::RetainRV) {
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// If we see two retains in a row on the same pointer. If so, make
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// a note, and we'll cicle back to revisit it after we've
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// hopefully eliminated the second retain, which may allow us to
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// eliminate the first retain too.
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// Theoretically we could implement removal of nested retain+release
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// pairs by making PtrState hold a stack of states, but this is
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// simple and avoids adding overhead for the non-nested case.
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if (GetSeq() == S_Retain)
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NestingDetected = true;
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ResetSequenceProgress(S_Retain);
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SetKnownSafe(HasKnownPositiveRefCount());
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InsertCall(I);
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}
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SetKnownPositiveRefCount();
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return NestingDetected;
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}
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bool TopDownPtrState::MatchWithRelease(ARCMDKindCache &Cache,
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Instruction *Release) {
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ClearKnownPositiveRefCount();
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Sequence OldSeq = GetSeq();
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MDNode *ReleaseMetadata =
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Release->getMetadata(Cache.get(ARCMDKindID::ImpreciseRelease));
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switch (OldSeq) {
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case S_Retain:
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case S_CanRelease:
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if (OldSeq == S_Retain || ReleaseMetadata != nullptr)
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ClearReverseInsertPts();
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LLVM_FALLTHROUGH;
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case S_Use:
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SetReleaseMetadata(ReleaseMetadata);
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SetTailCallRelease(cast<CallInst>(Release)->isTailCall());
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return true;
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case S_None:
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return false;
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case S_Stop:
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case S_Release:
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case S_MovableRelease:
|
||
|
|
llvm_unreachable("top-down pointer in bottom up state!");
|
||
|
|
}
|
||
|
|
llvm_unreachable("Sequence unknown enum value");
|
||
|
|
}
|
||
|
|
|
||
|
|
bool TopDownPtrState::HandlePotentialAlterRefCount(Instruction *Inst,
|
||
|
|
const Value *Ptr,
|
||
|
|
ProvenanceAnalysis &PA,
|
||
|
|
ARCInstKind Class) {
|
||
|
|
// Check for possible releases. Treat clang.arc.use as a releasing instruction
|
||
|
|
// to prevent sinking a retain past it.
|
||
|
|
if (!CanDecrementRefCount(Inst, Ptr, PA, Class) &&
|
||
|
|
Class != ARCInstKind::IntrinsicUser)
|
||
|
|
return false;
|
||
|
|
|
||
|
|
LLVM_DEBUG(dbgs() << " CanAlterRefCount: Seq: " << GetSeq() << "; "
|
||
|
|
<< *Ptr << "\n");
|
||
|
|
ClearKnownPositiveRefCount();
|
||
|
|
switch (GetSeq()) {
|
||
|
|
case S_Retain:
|
||
|
|
SetSeq(S_CanRelease);
|
||
|
|
assert(!HasReverseInsertPts());
|
||
|
|
InsertReverseInsertPt(Inst);
|
||
|
|
|
||
|
|
// One call can't cause a transition from S_Retain to S_CanRelease
|
||
|
|
// and S_CanRelease to S_Use. If we've made the first transition,
|
||
|
|
// we're done.
|
||
|
|
return true;
|
||
|
|
case S_Use:
|
||
|
|
case S_CanRelease:
|
||
|
|
case S_None:
|
||
|
|
return false;
|
||
|
|
case S_Stop:
|
||
|
|
case S_Release:
|
||
|
|
case S_MovableRelease:
|
||
|
|
llvm_unreachable("top-down pointer in release state!");
|
||
|
|
}
|
||
|
|
llvm_unreachable("covered switch is not covered!?");
|
||
|
|
}
|
||
|
|
|
||
|
|
void TopDownPtrState::HandlePotentialUse(Instruction *Inst, const Value *Ptr,
|
||
|
|
ProvenanceAnalysis &PA,
|
||
|
|
ARCInstKind Class) {
|
||
|
|
// Check for possible direct uses.
|
||
|
|
switch (GetSeq()) {
|
||
|
|
case S_CanRelease:
|
||
|
|
if (!CanUse(Inst, Ptr, PA, Class))
|
||
|
|
return;
|
||
|
|
LLVM_DEBUG(dbgs() << " CanUse: Seq: " << GetSeq() << "; "
|
||
|
|
<< *Ptr << "\n");
|
||
|
|
SetSeq(S_Use);
|
||
|
|
return;
|
||
|
|
case S_Retain:
|
||
|
|
case S_Use:
|
||
|
|
case S_None:
|
||
|
|
return;
|
||
|
|
case S_Stop:
|
||
|
|
case S_Release:
|
||
|
|
case S_MovableRelease:
|
||
|
|
llvm_unreachable("top-down pointer in release state!");
|
||
|
|
}
|
||
|
|
}
|