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https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-23 17:29:19 +00:00
Track a retain+release nesting level independently of the
known-incremented level, because the two concepts can be used to prove the saftey of a retain+release removal in different ways. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@138016 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
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b29ec06421
commit
e6d5e88c12
@ -877,7 +877,9 @@ bool ObjCARCExpand::runOnFunction(Function &F) {
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// usually can't sink them past other calls, which would be the main
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// case where it would be useful.
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/// TODO: The pointer returned from objc_loadWeakRetained is retained.
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// TODO: The pointer returned from objc_loadWeakRetained is retained.
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// TODO: Delete release+retain pairs (rare).
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#include "llvm/GlobalAlias.h"
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#include "llvm/Constants.h"
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@ -1124,13 +1126,19 @@ namespace {
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/// retain-decrement-use-release sequence or release-use-decrement-retain
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/// reverese sequence.
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struct RRInfo {
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/// KnownIncremented - After an objc_retain, the reference count of the
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/// referenced object is known to be positive. Similarly, before an
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/// objc_release, the reference count of the referenced object is known to
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/// be positive. If there are retain-release pairs in code regions where the
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/// retain count is known to be positive, they can be eliminated, regardless
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/// of any side effects between them.
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bool KnownIncremented;
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/// KnownSafe - After an objc_retain, the reference count of the referenced
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/// object is known to be positive. Similarly, before an objc_release, the
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/// reference count of the referenced object is known to be positive. If
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/// there are retain-release pairs in code regions where the retain count
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/// is known to be positive, they can be eliminated, regardless of any side
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/// effects between them.
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///
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/// Also, a retain+release pair nested within another retain+release
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/// pair all on the known same pointer value can be eliminated, regardless
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/// of any intervening side effects.
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///
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/// KnownSafe is true when either of these conditions is satisfied.
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bool KnownSafe;
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/// IsRetainBlock - True if the Calls are objc_retainBlock calls (as
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/// opposed to objc_retain calls).
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@ -1153,7 +1161,7 @@ namespace {
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SmallPtrSet<Instruction *, 2> ReverseInsertPts;
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RRInfo() :
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KnownIncremented(false), IsRetainBlock(false), IsTailCallRelease(false),
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KnownSafe(false), IsRetainBlock(false), IsTailCallRelease(false),
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ReleaseMetadata(0) {}
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void clear();
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@ -1161,7 +1169,7 @@ namespace {
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}
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void RRInfo::clear() {
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KnownIncremented = false;
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KnownSafe = false;
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IsRetainBlock = false;
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IsTailCallRelease = false;
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ReleaseMetadata = 0;
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@ -1176,6 +1184,9 @@ namespace {
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/// RefCount - The known minimum number of reference count increments.
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unsigned RefCount;
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/// NestCount - The known minimum level of retain+release nesting.
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unsigned NestCount;
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/// Seq - The current position in the sequence.
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Sequence Seq;
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@ -1184,7 +1195,7 @@ namespace {
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/// TODO: Encapsulate this better.
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RRInfo RRI;
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PtrState() : RefCount(0), Seq(S_None) {}
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PtrState() : RefCount(0), NestCount(0), Seq(S_None) {}
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void SetAtLeastOneRefCount() {
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if (RefCount == 0) RefCount = 1;
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@ -1202,6 +1213,18 @@ namespace {
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return RefCount > 0;
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}
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void IncrementNestCount() {
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if (NestCount != UINT_MAX) ++NestCount;
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}
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void DecrementNestCount() {
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if (NestCount != 0) --NestCount;
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}
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bool IsKnownNested() const {
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return NestCount > 0;
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}
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void SetSeq(Sequence NewSeq) {
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Seq = NewSeq;
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}
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@ -1233,6 +1256,7 @@ void
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PtrState::Merge(const PtrState &Other, bool TopDown) {
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Seq = MergeSeqs(Seq, Other.Seq, TopDown);
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RefCount = std::min(RefCount, Other.RefCount);
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NestCount = std::min(NestCount, Other.NestCount);
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// We can't merge a plain objc_retain with an objc_retainBlock.
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if (RRI.IsRetainBlock != Other.RRI.IsRetainBlock)
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@ -1245,7 +1269,7 @@ PtrState::Merge(const PtrState &Other, bool TopDown) {
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if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata)
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RRI.ReleaseMetadata = 0;
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RRI.KnownIncremented = RRI.KnownIncremented && Other.RRI.KnownIncremented;
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RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe;
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RRI.IsTailCallRelease = RRI.IsTailCallRelease && Other.RRI.IsTailCallRelease;
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RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end());
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RRI.ReverseInsertPts.insert(Other.RRI.ReverseInsertPts.begin(),
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@ -2166,7 +2190,7 @@ ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
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switch (SuccS.GetSeq()) {
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case S_None:
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case S_CanRelease: {
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if (!S.RRI.KnownIncremented && !SuccS.RRI.KnownIncremented)
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if (!S.RRI.KnownSafe && !SuccS.RRI.KnownSafe)
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S.ClearSequenceProgress();
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continue;
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}
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@ -2176,7 +2200,7 @@ ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
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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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if (!S.RRI.KnownIncremented && !SuccS.RRI.KnownIncremented)
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if (!S.RRI.KnownSafe && !SuccS.RRI.KnownSafe)
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AllSuccsHaveSame = false;
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break;
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case S_Retain:
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@ -2199,7 +2223,7 @@ ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
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PtrState &SuccS = BBStates[*SI].getPtrBottomUpState(Arg);
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switch (SuccS.GetSeq()) {
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case S_None: {
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if (!S.RRI.KnownIncremented && !SuccS.RRI.KnownIncremented)
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if (!S.RRI.KnownSafe && !SuccS.RRI.KnownSafe)
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S.ClearSequenceProgress();
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continue;
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}
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@ -2210,7 +2234,7 @@ ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
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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 (!S.RRI.KnownIncremented && !SuccS.RRI.KnownIncremented)
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if (!S.RRI.KnownSafe && !SuccS.RRI.KnownSafe)
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AllSuccsHaveSame = false;
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break;
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case S_Retain:
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@ -2285,11 +2309,12 @@ ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
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S.SetSeqToRelease(Inst->getMetadata(ImpreciseReleaseMDKind));
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S.RRI.clear();
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S.RRI.KnownIncremented = S.IsKnownIncremented();
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S.RRI.KnownSafe = S.IsKnownNested() || S.IsKnownIncremented();
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S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
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S.RRI.Calls.insert(Inst);
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S.IncrementRefCount();
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S.IncrementNestCount();
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break;
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}
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case IC_RetainBlock:
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@ -2300,6 +2325,7 @@ ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
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PtrState &S = MyStates.getPtrBottomUpState(Arg);
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S.DecrementRefCount();
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S.SetAtLeastOneRefCount();
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S.DecrementNestCount();
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switch (S.GetSeq()) {
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case S_Stop:
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@ -2322,7 +2348,7 @@ ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
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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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break;
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continue;
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}
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case IC_AutoreleasepoolPop:
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// Conservatively, clear MyStates for all known pointers.
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@ -2346,11 +2372,9 @@ ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
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PtrState &S = MI->second;
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Sequence Seq = S.GetSeq();
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// Check for possible releases. Note that we don't have to update
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// S's RefCount because any reference count modifications would be
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// done through a different provenance.
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if (!IsRetain(Class) && Class != IC_RetainBlock &&
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CanAlterRefCount(Inst, Ptr, PA, Class))
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// Check for possible releases.
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if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
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S.DecrementRefCount();
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switch (Seq) {
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case S_Use:
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S.SetSeq(S_CanRelease);
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@ -2364,6 +2388,7 @@ ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
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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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// Check for possible direct uses.
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switch (Seq) {
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@ -2464,19 +2489,23 @@ ObjCARCOpt::VisitTopDown(BasicBlock *BB,
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S.SetSeq(S_Retain);
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S.RRI.clear();
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S.RRI.IsRetainBlock = Class == IC_RetainBlock;
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S.RRI.KnownIncremented = S.IsKnownIncremented();
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// Don't check S.IsKnownIncremented() here because it's not
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// sufficient.
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S.RRI.KnownSafe = S.IsKnownNested();
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S.RRI.Calls.insert(Inst);
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}
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S.SetAtLeastOneRefCount();
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S.IncrementRefCount();
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break;
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S.IncrementNestCount();
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continue;
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}
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case IC_Release: {
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Arg = GetObjCArg(Inst);
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PtrState &S = MyStates.getPtrTopDownState(Arg);
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S.DecrementRefCount();
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S.DecrementNestCount();
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switch (S.GetSeq()) {
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case S_Retain:
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@ -2520,11 +2549,9 @@ ObjCARCOpt::VisitTopDown(BasicBlock *BB,
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PtrState &S = MI->second;
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Sequence Seq = S.GetSeq();
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// Check for possible releases. Note that we don't have to update
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// S's RefCount because any reference count modifications would be
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// done through a different provenance.
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if (!IsRetain(Class) && Class != IC_RetainBlock &&
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CanAlterRefCount(Inst, Ptr, PA, Class))
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// Check for possible releases.
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if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
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S.DecrementRefCount();
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switch (Seq) {
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case S_Retain:
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S.SetSeq(S_CanRelease);
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@ -2544,6 +2571,7 @@ ObjCARCOpt::VisitTopDown(BasicBlock *BB,
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case S_MovableRelease:
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llvm_unreachable("top-down pointer in release state!");
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}
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}
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// Check for possible direct uses.
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switch (Seq) {
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@ -2718,7 +2746,7 @@ ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
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// If a pair happens in a region where it is known that the reference count
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// is already incremented, we can similarly ignore possible decrements.
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bool KnownIncrementedTD = true, KnownIncrementedBU = true;
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bool KnownSafeTD = true, KnownSafeBU = true;
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// Connect the dots between the top-down-collected RetainsToMove and
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// bottom-up-collected ReleasesToMove to form sets of related calls.
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@ -2738,7 +2766,7 @@ ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
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MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain);
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assert(It != Retains.end());
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const RRInfo &NewRetainRRI = It->second;
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KnownIncrementedTD &= NewRetainRRI.KnownIncremented;
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KnownSafeTD &= NewRetainRRI.KnownSafe;
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for (SmallPtrSet<Instruction *, 2>::const_iterator
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LI = NewRetainRRI.Calls.begin(),
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LE = NewRetainRRI.Calls.end(); LI != LE; ++LI) {
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@ -2794,7 +2822,7 @@ ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
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Releases.find(NewRelease);
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assert(It != Releases.end());
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const RRInfo &NewReleaseRRI = It->second;
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KnownIncrementedBU &= NewReleaseRRI.KnownIncremented;
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KnownSafeBU &= NewReleaseRRI.KnownSafe;
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for (SmallPtrSet<Instruction *, 2>::const_iterator
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LI = NewReleaseRRI.Calls.begin(),
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LE = NewReleaseRRI.Calls.end(); LI != LE; ++LI) {
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@ -2842,9 +2870,9 @@ ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
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if (NewRetains.empty()) break;
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}
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// If the pointer is known incremented, we can safely delete the pair
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// regardless of what's between them.
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if (KnownIncrementedTD || KnownIncrementedBU) {
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// If the pointer is known incremented or nested, we can safely delete the
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// pair regardless of what's between them.
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if (KnownSafeTD || KnownSafeBU) {
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RetainsToMove.ReverseInsertPts.clear();
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ReleasesToMove.ReverseInsertPts.clear();
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NewCount = 0;
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@ -1569,6 +1569,74 @@ if.end: ; preds = %entry, %if.then
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ret void
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}
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; When there are adjacent retain+release pairs, the first one is
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; known unnecessary because the presence of the second one means that
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; the first one won't be deleting the object.
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; CHECK: define void @test57(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: call void @use_pointer(i8* %x)
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; CHECK-NEXT: call void @use_pointer(i8* %x)
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; CHECK-NEXT: %0 = tail call i8* @objc_retain(i8* %x) nounwind
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; CHECK-NEXT: call void @use_pointer(i8* %x)
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; CHECK-NEXT: call void @use_pointer(i8* %x)
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; CHECK-NEXT: call void @objc_release(i8* %x) nounwind
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; CHECK-NEXT: ret void
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; CHECK-NEXT: }
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define void @test57(i8* %x) nounwind {
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entry:
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call i8* @objc_retain(i8* %x) nounwind
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call void @use_pointer(i8* %x)
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call void @use_pointer(i8* %x)
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call void @objc_release(i8* %x) nounwind
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call i8* @objc_retain(i8* %x) nounwind
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call void @use_pointer(i8* %x)
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call void @use_pointer(i8* %x)
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call void @objc_release(i8* %x) nounwind
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ret void
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}
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; An adjacent retain+release pair is sufficient even if it will be
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; removed itself.
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; CHECK: define void @test58(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: call void @use_pointer(i8* %x)
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; CHECK-NEXT: call void @use_pointer(i8* %x)
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; CHECK-NEXT: ret void
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; CHECK-NEXT: }
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define void @test58(i8* %x) nounwind {
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entry:
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call i8* @objc_retain(i8* %x) nounwind
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call void @use_pointer(i8* %x)
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call void @use_pointer(i8* %x)
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call void @objc_release(i8* %x) nounwind
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call i8* @objc_retain(i8* %x) nounwind
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call void @objc_release(i8* %x) nounwind
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ret void
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}
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; Don't delete the second retain+release pair in an adjacent set.
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; CHECK: define void @test59(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: %0 = tail call i8* @objc_retain(i8* %x) nounwind
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; CHECK-NEXT: call void @use_pointer(i8* %x)
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; CHECK-NEXT: call void @use_pointer(i8* %x)
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; CHECK-NEXT: call void @objc_release(i8* %x) nounwind
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; CHECK-NEXT: ret void
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; CHECK-NEXT: }
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define void @test59(i8* %x) nounwind {
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entry:
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%a = call i8* @objc_retain(i8* %x) nounwind
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call void @objc_release(i8* %x) nounwind
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%b = call i8* @objc_retain(i8* %x) nounwind
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call void @use_pointer(i8* %x)
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call void @use_pointer(i8* %x)
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call void @objc_release(i8* %x) nounwind
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ret void
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}
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declare void @bar(i32 ()*)
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; A few real-world testcases.
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