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Teach the ARC optimizer about the !clang.arc.copy_on_escape metadata
tag on objc_retainBlock calls, which indicates that they may be optimized away. rdar://10211286. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142298 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
parent
fa1ee88052
commit
a974beaa1f
@ -1154,6 +1154,10 @@ namespace {
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/// opposed to objc_retain calls).
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bool IsRetainBlock;
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/// CopyOnEscape - True if this the Calls are objc_retainBlock calls
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/// which all have the !clang.arc.copy_on_escape metadata.
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bool CopyOnEscape;
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/// IsTailCallRelease - True of the objc_release calls are all marked
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/// with the "tail" keyword.
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bool IsTailCallRelease;
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@ -1176,8 +1180,8 @@ namespace {
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SmallPtrSet<Instruction *, 2> ReverseInsertPts;
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RRInfo() :
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KnownSafe(false), IsRetainBlock(false), IsTailCallRelease(false),
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Partial(false),
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KnownSafe(false), IsRetainBlock(false), CopyOnEscape(false),
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IsTailCallRelease(false), Partial(false),
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ReleaseMetadata(0) {}
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void clear();
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@ -1187,6 +1191,7 @@ namespace {
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void RRInfo::clear() {
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KnownSafe = false;
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IsRetainBlock = false;
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CopyOnEscape = false;
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IsTailCallRelease = false;
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Partial = false;
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ReleaseMetadata = 0;
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@ -1294,6 +1299,7 @@ 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.CopyOnEscape = RRI.CopyOnEscape && Other.RRI.CopyOnEscape;
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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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@ -1482,6 +1488,10 @@ namespace {
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/// metadata.
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unsigned ImpreciseReleaseMDKind;
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/// CopyOnEscape - The Metadata Kind for clang.arc.copy_on_escape
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/// metadata.
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unsigned CopyOnEscapeMDKind;
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Constant *getRetainRVCallee(Module *M);
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Constant *getAutoreleaseRVCallee(Module *M);
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Constant *getReleaseCallee(Module *M);
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@ -2360,9 +2370,12 @@ ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
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S.SetAtLeastOneRefCount();
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S.DecrementNestCount();
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// An objc_retainBlock call with just a use still needs to be kept,
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// because it may be copying a block from the stack to the heap.
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if (Class == IC_RetainBlock && S.GetSeq() == S_Use)
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// An non-copy-on-escape objc_retainBlock call with just a use still
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// needs to be kept, because it may be copying a block from the stack
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// to the heap.
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if (Class == IC_RetainBlock &&
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!Inst->getMetadata(CopyOnEscapeMDKind) &&
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S.GetSeq() == S_Use)
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S.SetSeq(S_CanRelease);
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switch (S.GetSeq()) {
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@ -2377,6 +2390,8 @@ ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
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// better to let it remain as the first instruction after a call.
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if (Class != IC_RetainRV) {
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S.RRI.IsRetainBlock = Class == IC_RetainBlock;
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if (S.RRI.IsRetainBlock)
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S.RRI.CopyOnEscape = !!Inst->getMetadata(CopyOnEscapeMDKind);
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Retains[Inst] = S.RRI;
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}
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S.ClearSequenceProgress();
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@ -2527,6 +2542,8 @@ 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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if (S.RRI.IsRetainBlock)
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S.RRI.CopyOnEscape = !!Inst->getMetadata(CopyOnEscapeMDKind);
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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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@ -2618,10 +2635,11 @@ ObjCARCOpt::VisitTopDown(BasicBlock *BB,
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S.SetSeq(S_Use);
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break;
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case S_Retain:
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// An objc_retainBlock call may be responsible for copying the block
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// data from the stack to the heap. Model this by moving it straight
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// from S_Retain to S_Use.
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// A non-copy-on-scape objc_retainBlock call may be responsible for
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// copying the block data from the stack to the heap. Model this by
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// moving it straight from S_Retain to S_Use.
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if (S.RRI.IsRetainBlock &&
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!S.RRI.CopyOnEscape &&
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CanUse(Inst, Ptr, PA, Class)) {
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assert(S.RRI.ReverseInsertPts.empty());
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S.RRI.ReverseInsertPts.insert(Inst);
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@ -2713,6 +2731,9 @@ void ObjCARCOpt::MoveCalls(Value *Arg,
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getRetainBlockCallee(M) : getRetainCallee(M),
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MyArg, "", InsertPt);
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Call->setDoesNotThrow();
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if (RetainsToMove.CopyOnEscape)
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Call->setMetadata(CopyOnEscapeMDKind,
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MDNode::get(M->getContext(), ArrayRef<Value *>()));
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if (!RetainsToMove.IsRetainBlock)
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Call->setTailCall();
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}
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@ -2792,10 +2813,11 @@ ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
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// regardless of what possible decrements or uses lie between them.
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bool KnownSafe = isa<Constant>(Arg);
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// Same for stack storage, unless this is an objc_retainBlock call,
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// which is responsible for copying the block data from the stack to
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// the heap.
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if (!I->second.IsRetainBlock && isa<AllocaInst>(Arg))
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// Same for stack storage, unless this is a non-copy-on-escape
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// objc_retainBlock call, which is responsible for copying the block data
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// from the stack to the heap.
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if ((!I->second.IsRetainBlock || I->second.CopyOnEscape) &&
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isa<AllocaInst>(Arg))
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KnownSafe = true;
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// A constant pointer can't be pointing to an object on the heap. It may
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@ -2905,6 +2927,7 @@ ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
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// Merge the IsRetainBlock values.
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if (FirstRetain) {
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RetainsToMove.IsRetainBlock = NewReleaseRetainRRI.IsRetainBlock;
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RetainsToMove.CopyOnEscape = NewReleaseRetainRRI.CopyOnEscape;
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FirstRetain = false;
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} else if (ReleasesToMove.IsRetainBlock !=
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NewReleaseRetainRRI.IsRetainBlock)
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@ -2912,6 +2935,9 @@ ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
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// objc_retain and the other uses objc_retainBlock.
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goto next_retain;
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// Merge the CopyOnEscape values.
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RetainsToMove.CopyOnEscape &= NewReleaseRetainRRI.CopyOnEscape;
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// Collect the optimal insertion points.
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if (!KnownSafe)
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for (SmallPtrSet<Instruction *, 2>::const_iterator
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@ -3265,6 +3291,8 @@ bool ObjCARCOpt::doInitialization(Module &M) {
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// Identify the imprecise release metadata kind.
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ImpreciseReleaseMDKind =
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M.getContext().getMDKindID("clang.imprecise_release");
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CopyOnEscapeMDKind =
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M.getContext().getMDKindID("clang.arc.copy_on_escape");
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// Intuitively, objc_retain and others are nocapture, however in practice
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// they are not, because they return their argument value. And objc_release
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@ -1,11 +1,6 @@
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; RUN: opt -S -objc-arc < %s | FileCheck %s
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; rdar://10209613
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; CHECK: define void @test
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; CHECK: %3 = call i8* @objc_retainBlock(i8* %2) nounwind
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; CHECK: @objc_msgSend
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; CHECK-NEXT: @objc_release(i8* %3)
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%0 = type opaque
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%struct.__block_descriptor = type { i64, i64 }
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@ -13,6 +8,10 @@
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@__block_descriptor_tmp = external hidden constant { i64, i64, i8*, i8*, i8*, i8* }
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@"\01L_OBJC_SELECTOR_REFERENCES_" = external hidden global i8*, section "__DATA, __objc_selrefs, literal_pointers, no_dead_strip"
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; CHECK: define void @test(
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; CHECK: %3 = call i8* @objc_retainBlock(i8* %2) nounwind
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; CHECK: @objc_msgSend
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; CHECK-NEXT: @objc_release(i8* %3)
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define void @test(%0* %array) uwtable {
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entry:
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%block = alloca <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, %0* }>, align 8
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@ -41,6 +40,43 @@ entry:
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ret void
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}
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; Same as test, but the objc_retainBlock has a clang.arc.copy_on_escape
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; tag so it's safe to delete.
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; CHECK: define void @test_with_COE(
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; CHECK-NOT: @objc_retainBlock
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; CHECK: @objc_msgSend
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; CHECK: @objc_release
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; CHECK-NOT: @objc_release
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; CHECK: }
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define void @test_with_COE(%0* %array) uwtable {
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entry:
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%block = alloca <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, %0* }>, align 8
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%0 = bitcast %0* %array to i8*
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%1 = tail call i8* @objc_retain(i8* %0) nounwind
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%block.isa = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, %0* }>* %block, i64 0, i32 0
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store i8* bitcast (i8** @_NSConcreteStackBlock to i8*), i8** %block.isa, align 8
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%block.flags = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, %0* }>* %block, i64 0, i32 1
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store i32 1107296256, i32* %block.flags, align 8
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%block.reserved = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, %0* }>* %block, i64 0, i32 2
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store i32 0, i32* %block.reserved, align 4
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%block.invoke = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, %0* }>* %block, i64 0, i32 3
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store i8* bitcast (void (i8*)* @__test_block_invoke_0 to i8*), i8** %block.invoke, align 8
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%block.descriptor = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, %0* }>* %block, i64 0, i32 4
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store %struct.__block_descriptor* bitcast ({ i64, i64, i8*, i8*, i8*, i8* }* @__block_descriptor_tmp to %struct.__block_descriptor*), %struct.__block_descriptor** %block.descriptor, align 8
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%block.captured = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, %0* }>* %block, i64 0, i32 5
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store %0* %array, %0** %block.captured, align 8
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%2 = bitcast <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, %0* }>* %block to i8*
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%3 = call i8* @objc_retainBlock(i8* %2) nounwind, !clang.arc.copy_on_escape !0
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%tmp2 = load i8** @"\01L_OBJC_SELECTOR_REFERENCES_", align 8
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call void bitcast (i8* (i8*, i8*, ...)* @objc_msgSend to void (i8*, i8*, i8*)*)(i8* %0, i8* %tmp2, i8* %3)
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call void @objc_release(i8* %3) nounwind
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%strongdestroy = load %0** %block.captured, align 8
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%4 = bitcast %0* %strongdestroy to i8*
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call void @objc_release(i8* %4) nounwind, !clang.imprecise_release !0
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ret void
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}
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declare i8* @objc_retain(i8*)
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declare void @__test_block_invoke_0(i8* nocapture) uwtable
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