From 728db4997a104335904ebbfafbf767f3c492250d Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Fri, 13 Jan 2012 00:39:07 +0000 Subject: [PATCH] Implement proper ObjC ARC objc_retainBlock "escape" analysis, so that the optimizer doesn't eliminate objc_retainBlock calls which are needed for their side effect of copying blocks onto the heap. This implements rdar://10361249. llvm-svn: 148076 --- llvm/lib/Transforms/Scalar/ObjCARC.cpp | 108 +++++++++------ llvm/test/Transforms/ObjCARC/basic.ll | 19 ++- llvm/test/Transforms/ObjCARC/retain-block.ll | 138 +++++++++++++++++++ 3 files changed, 218 insertions(+), 47 deletions(-) create mode 100644 llvm/test/Transforms/ObjCARC/retain-block.ll diff --git a/llvm/lib/Transforms/Scalar/ObjCARC.cpp b/llvm/lib/Transforms/Scalar/ObjCARC.cpp index b017ba11d829..0cf314860842 100644 --- a/llvm/lib/Transforms/Scalar/ObjCARC.cpp +++ b/llvm/lib/Transforms/Scalar/ObjCARC.cpp @@ -601,6 +601,36 @@ static bool ModuleHasARC(const Module &M) { M.getNamedValue("objc_unretainedPointer"); } +/// DoesObjCBlockEscape - Test whether the given pointer, which is an +/// Objective C block pointer, does not "escape". This differs from regular +/// escape analysis in that a use as an argument to a call is not considered +/// an escape. +static bool DoesObjCBlockEscape(const Value *BlockPtr) { + // Walk the def-use chains. + SmallVector Worklist; + Worklist.push_back(BlockPtr); + do { + const Value *V = Worklist.pop_back_val(); + for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end(); + UI != UE; ++UI) { + const User *UUser = *UI; + // Special - Use by a call (callee or argument) is not considered + // to be an escape. + if (ImmutableCallSite CS = cast(UUser)) + continue; + if (isa(UUser) || isa(UUser) || + isa(UUser) || isa(UUser)) { + Worklist.push_back(UUser); + continue; + } + return true; + } + } while (!Worklist.empty()); + + // No escapes found. + return false; +} + //===----------------------------------------------------------------------===// // ARC AliasAnalysis. //===----------------------------------------------------------------------===// @@ -1159,10 +1189,6 @@ namespace { /// opposed to objc_retain calls). bool IsRetainBlock; - /// CopyOnEscape - True if this the Calls are objc_retainBlock calls - /// which all have the !clang.arc.copy_on_escape metadata. - bool CopyOnEscape; - /// IsTailCallRelease - True of the objc_release calls are all marked /// with the "tail" keyword. bool IsTailCallRelease; @@ -1186,7 +1212,7 @@ namespace { SmallPtrSet ReverseInsertPts; RRInfo() : - KnownSafe(false), IsRetainBlock(false), CopyOnEscape(false), + KnownSafe(false), IsRetainBlock(false), IsTailCallRelease(false), Partial(false), ReleaseMetadata(0) {} @@ -1197,7 +1223,6 @@ namespace { void RRInfo::clear() { KnownSafe = false; IsRetainBlock = false; - CopyOnEscape = false; IsTailCallRelease = false; Partial = false; ReleaseMetadata = 0; @@ -1295,7 +1320,6 @@ PtrState::Merge(const PtrState &Other, bool TopDown) { if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata) RRI.ReleaseMetadata = 0; - RRI.CopyOnEscape = RRI.CopyOnEscape && Other.RRI.CopyOnEscape; RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe; RRI.IsTailCallRelease = RRI.IsTailCallRelease && Other.RRI.IsTailCallRelease; RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end()); @@ -1495,6 +1519,8 @@ namespace { Constant *getRetainBlockCallee(Module *M); Constant *getAutoreleaseCallee(Module *M); + bool IsRetainBlockOptimizable(const Instruction *Inst); + void OptimizeRetainCall(Function &F, Instruction *Retain); bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV); void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV); @@ -1562,6 +1588,22 @@ void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesCFG(); } +bool ObjCARCOpt::IsRetainBlockOptimizable(const Instruction *Inst) { + // Without the magic metadata tag, we have to assume this might be an + // objc_retainBlock call inserted to convert a block pointer to an id, + // in which case it really is needed. + if (!Inst->getMetadata(CopyOnEscapeMDKind)) + return false; + + // If the pointer "escapes" (not including being used in a call), + // the copy may be needed. + if (DoesObjCBlockEscape(Inst)) + return false; + + // Otherwise, it's not needed. + return true; +} + Constant *ObjCARCOpt::getRetainRVCallee(Module *M) { if (!RetainRVCallee) { LLVMContext &C = M->getContext(); @@ -2362,6 +2404,11 @@ ObjCARCOpt::VisitBottomUp(BasicBlock *BB, break; } case IC_RetainBlock: + // An objc_retainBlock call with just a use may need to be kept, + // because it may be copying a block from the stack to the heap. + if (!IsRetainBlockOptimizable(Inst)) + break; + // FALLTHROUGH case IC_Retain: case IC_RetainRV: { Arg = GetObjCArg(Inst); @@ -2371,14 +2418,6 @@ ObjCARCOpt::VisitBottomUp(BasicBlock *BB, S.SetAtLeastOneRefCount(); S.DecrementNestCount(); - // An non-copy-on-escape objc_retainBlock call with just a use still - // needs to be kept, because it may be copying a block from the stack - // to the heap. - if (Class == IC_RetainBlock && - !Inst->getMetadata(CopyOnEscapeMDKind) && - S.GetSeq() == S_Use) - S.SetSeq(S_CanRelease); - switch (S.GetSeq()) { case S_Stop: case S_Release: @@ -2391,8 +2430,6 @@ ObjCARCOpt::VisitBottomUp(BasicBlock *BB, // better to let it remain as the first instruction after a call. if (Class != IC_RetainRV) { S.RRI.IsRetainBlock = Class == IC_RetainBlock; - if (S.RRI.IsRetainBlock) - S.RRI.CopyOnEscape = !!Inst->getMetadata(CopyOnEscapeMDKind); Retains[Inst] = S.RRI; } S.ClearSequenceProgress(); @@ -2519,6 +2556,11 @@ ObjCARCOpt::VisitTopDown(BasicBlock *BB, switch (Class) { case IC_RetainBlock: + // An objc_retainBlock call with just a use may need to be kept, + // because it may be copying a block from the stack to the heap. + if (!IsRetainBlockOptimizable(Inst)) + break; + // FALLTHROUGH case IC_Retain: case IC_RetainRV: { Arg = GetObjCArg(Inst); @@ -2541,8 +2583,6 @@ ObjCARCOpt::VisitTopDown(BasicBlock *BB, S.SetSeq(S_Retain); S.RRI.clear(); S.RRI.IsRetainBlock = Class == IC_RetainBlock; - if (S.RRI.IsRetainBlock) - S.RRI.CopyOnEscape = !!Inst->getMetadata(CopyOnEscapeMDKind); // Don't check S.IsKnownIncremented() here because it's not // sufficient. S.RRI.KnownSafe = S.IsKnownNested(); @@ -2634,17 +2674,6 @@ ObjCARCOpt::VisitTopDown(BasicBlock *BB, S.SetSeq(S_Use); break; case S_Retain: - // A non-copy-on-scape objc_retainBlock call may be responsible for - // copying the block data from the stack to the heap. Model this by - // moving it straight from S_Retain to S_Use. - if (S.RRI.IsRetainBlock && - !S.RRI.CopyOnEscape && - CanUse(Inst, Ptr, PA, Class)) { - assert(S.RRI.ReverseInsertPts.empty()); - S.RRI.ReverseInsertPts.insert(Inst); - S.SetSeq(S_Use); - } - break; case S_Use: case S_None: break; @@ -2787,10 +2816,10 @@ void ObjCARCOpt::MoveCalls(Value *Arg, getRetainBlockCallee(M) : getRetainCallee(M), MyArg, "", InsertPt); Call->setDoesNotThrow(); - if (RetainsToMove.CopyOnEscape) + if (RetainsToMove.IsRetainBlock) Call->setMetadata(CopyOnEscapeMDKind, MDNode::get(M->getContext(), ArrayRef())); - if (!RetainsToMove.IsRetainBlock) + else Call->setTailCall(); } for (SmallPtrSet::const_iterator @@ -2864,18 +2893,11 @@ ObjCARCOpt::PerformCodePlacement(DenseMap Instruction *Retain = cast(V); Value *Arg = GetObjCArg(Retain); - // If the object being released is in static storage, we know it's + // If the object being released is in static or stack storage, we know it's // not being managed by ObjC reference counting, so we can delete pairs // regardless of what possible decrements or uses lie between them. - bool KnownSafe = isa(Arg); + bool KnownSafe = isa(Arg) || isa(Arg); - // Same for stack storage, unless this is a non-copy-on-escape - // objc_retainBlock call, which is responsible for copying the block data - // from the stack to the heap. - if ((!I->second.IsRetainBlock || I->second.CopyOnEscape) && - isa(Arg)) - KnownSafe = true; - // A constant pointer can't be pointing to an object on the heap. It may // be reference-counted, but it won't be deleted. if (const LoadInst *LI = dyn_cast(Arg)) @@ -2983,7 +3005,6 @@ ObjCARCOpt::PerformCodePlacement(DenseMap // Merge the IsRetainBlock values. if (FirstRetain) { RetainsToMove.IsRetainBlock = NewReleaseRetainRRI.IsRetainBlock; - RetainsToMove.CopyOnEscape = NewReleaseRetainRRI.CopyOnEscape; FirstRetain = false; } else if (ReleasesToMove.IsRetainBlock != NewReleaseRetainRRI.IsRetainBlock) @@ -2991,9 +3012,6 @@ ObjCARCOpt::PerformCodePlacement(DenseMap // objc_retain and the other uses objc_retainBlock. goto next_retain; - // Merge the CopyOnEscape values. - RetainsToMove.CopyOnEscape &= NewReleaseRetainRRI.CopyOnEscape; - // Collect the optimal insertion points. if (!KnownSafe) for (SmallPtrSet::const_iterator diff --git a/llvm/test/Transforms/ObjCARC/basic.ll b/llvm/test/Transforms/ObjCARC/basic.ll index 44c2602e5754..552f4e0b96ca 100644 --- a/llvm/test/Transforms/ObjCARC/basic.ll +++ b/llvm/test/Transforms/ObjCARC/basic.ll @@ -786,7 +786,7 @@ C: @__block_holder_tmp_1 = external constant %block1 define void @test23() { entry: - %0 = call i8* @objc_retainBlock(i8* bitcast (%block1* @__block_holder_tmp_1 to i8*)) nounwind + %0 = call i8* @objc_retainBlock(i8* bitcast (%block1* @__block_holder_tmp_1 to i8*)) nounwind, !clang.arc.copy_on_escape !0 call void @bar(i32 ()* bitcast (%block1* @__block_holder_tmp_1 to i32 ()*)) call void @bar(i32 ()* bitcast (%block1* @__block_holder_tmp_1 to i32 ()*)) call void @objc_release(i8* bitcast (%block1* @__block_holder_tmp_1 to i8*)) nounwind @@ -801,13 +801,28 @@ entry: ; CHECK: } define void @test23b(i8* %p) { entry: - %0 = call i8* @objc_retainBlock(i8* %p) nounwind + %0 = call i8* @objc_retainBlock(i8* %p) nounwind, !clang.arc.copy_on_escape !0 call void @callee() call void @use_pointer(i8* %p) call void @objc_release(i8* %p) nounwind ret void } +; Don't optimize objc_retainBlock, because there's no copy_on_escape metadata. + +; CHECK: define void @test23c( +; CHECK: @objc_retainBlock +; CHECK: @objc_release +; CHECK: } +define void @test23c() { +entry: + %0 = call i8* @objc_retainBlock(i8* bitcast (%block1* @__block_holder_tmp_1 to i8*)) nounwind + call void @bar(i32 ()* bitcast (%block1* @__block_holder_tmp_1 to i32 ()*)) + call void @bar(i32 ()* bitcast (%block1* @__block_holder_tmp_1 to i32 ()*)) + call void @objc_release(i8* bitcast (%block1* @__block_holder_tmp_1 to i8*)) nounwind + ret void +} + ; Any call can decrement a retain count. ; CHECK: define void @test24( diff --git a/llvm/test/Transforms/ObjCARC/retain-block.ll b/llvm/test/Transforms/ObjCARC/retain-block.ll new file mode 100644 index 000000000000..b3b62d300008 --- /dev/null +++ b/llvm/test/Transforms/ObjCARC/retain-block.ll @@ -0,0 +1,138 @@ +; RUN: opt -objc-arc -S < %s | FileCheck %s + +target datalayout = "e-p:64:64:64" + +!0 = metadata !{} + +declare i8* @objc_retain(i8*) +declare void @callee(i8) +declare void @use_pointer(i8*) +declare void @objc_release(i8*) +declare i8* @objc_retainBlock(i8*) +declare i8* @objc_autorelease(i8*) + +; Basic retainBlock+release elimination. + +; CHECK: define void @test0(i8* %tmp) { +; CHECK-NOT: @objc +; CHECK: } +define void @test0(i8* %tmp) { +entry: + %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind, !clang.arc.copy_on_escape !0 + tail call void @use_pointer(i8* %tmp2) + tail call void @objc_release(i8* %tmp2) nounwind, !clang.imprecise_release !0 + ret void +} + +; Same as test0, but there's no copy_on_escape metadata, so there's no +; optimization possible. + +; CHECK: define void @test0_no_metadata(i8* %tmp) { +; CHECK: %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind +; CHECK: tail call void @objc_release(i8* %tmp2) nounwind, !clang.imprecise_release !0 +; CHECK: } +define void @test0_no_metadata(i8* %tmp) { +entry: + %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind + tail call void @use_pointer(i8* %tmp2) + tail call void @objc_release(i8* %tmp2) nounwind, !clang.imprecise_release !0 + ret void +} + +; Same as test0, but the pointer escapes, so there's no +; optimization possible. + +; CHECK: define void @test0_escape(i8* %tmp, i8** %z) { +; CHECK: %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind, !clang.arc.copy_on_escape !0 +; CHECK: tail call void @objc_release(i8* %tmp2) nounwind, !clang.imprecise_release !0 +; CHECK: } +define void @test0_escape(i8* %tmp, i8** %z) { +entry: + %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind, !clang.arc.copy_on_escape !0 + store i8* %tmp2, i8** %z + tail call void @use_pointer(i8* %tmp2) + tail call void @objc_release(i8* %tmp2) nounwind, !clang.imprecise_release !0 + ret void +} + +; Same as test0_escape, but there's no intervening call. + +; CHECK: define void @test0_just_escape(i8* %tmp, i8** %z) { +; CHECK: %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind, !clang.arc.copy_on_escape !0 +; CHECK: tail call void @objc_release(i8* %tmp2) nounwind, !clang.imprecise_release !0 +; CHECK: } +define void @test0_just_escape(i8* %tmp, i8** %z) { +entry: + %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind, !clang.arc.copy_on_escape !0 + store i8* %tmp2, i8** %z + tail call void @objc_release(i8* %tmp2) nounwind, !clang.imprecise_release !0 + ret void +} + +; Basic nested retainBlock+release elimination. + +; CHECK: define void @test1(i8* %tmp) { +; CHECK-NOT: @objc +; CHECK: tail call i8* @objc_retain(i8* %tmp) nounwind +; CHECK-NOT: @objc +; CHECK: tail call void @objc_release(i8* %tmp) nounwind, !clang.imprecise_release !0 +; CHECK-NOT: @objc +; CHECK: } +define void @test1(i8* %tmp) { +entry: + %tmp1 = tail call i8* @objc_retain(i8* %tmp) nounwind + %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind, !clang.arc.copy_on_escape !0 + tail call void @use_pointer(i8* %tmp2) + tail call void @use_pointer(i8* %tmp2) + tail call void @objc_release(i8* %tmp2) nounwind, !clang.imprecise_release !0 + tail call void @objc_release(i8* %tmp) nounwind, !clang.imprecise_release !0 + ret void +} + +; Same as test1, but there's no copy_on_escape metadata, so there's no +; retainBlock+release optimization possible. But we can still eliminate +; the outer retain+release. + +; CHECK: define void @test1_no_metadata(i8* %tmp) { +; CHECK-NEXT: entry: +; CHECK-NEXT: tail call i8* @objc_retainBlock(i8* %tmp) nounwind +; CHECK-NEXT: @use_pointer(i8* %tmp2) +; CHECK-NEXT: @use_pointer(i8* %tmp2) +; CHECK-NEXT: tail call void @objc_release(i8* %tmp) nounwind, !clang.imprecise_release !0 +; CHECK-NOT: @objc +; CHECK: } +define void @test1_no_metadata(i8* %tmp) { +entry: + %tmp1 = tail call i8* @objc_retain(i8* %tmp) nounwind + %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind + tail call void @use_pointer(i8* %tmp2) + tail call void @use_pointer(i8* %tmp2) + tail call void @objc_release(i8* %tmp2) nounwind, !clang.imprecise_release !0 + tail call void @objc_release(i8* %tmp) nounwind, !clang.imprecise_release !0 + ret void +} + +; Same as test1, but the pointer escapes, so there's no +; retainBlock+release optimization possible. But we can still eliminate +; the outer retain+release + +; CHECK: define void @test1_escape(i8* %tmp, i8** %z) { +; CHECK-NEXT: entry: +; CHECK-NEXT: %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind, !clang.arc.copy_on_escape !0 +; CHECK-NEXT: store i8* %tmp2, i8** %z +; CHECK-NEXT: @use_pointer(i8* %tmp2) +; CHECK-NEXT: @use_pointer(i8* %tmp2) +; CHECK-NEXT: tail call void @objc_release(i8* %tmp) nounwind, !clang.imprecise_release !0 +; CHECK-NOT: @objc +; CHECK: } +define void @test1_escape(i8* %tmp, i8** %z) { +entry: + %tmp1 = tail call i8* @objc_retain(i8* %tmp) nounwind + %tmp2 = tail call i8* @objc_retainBlock(i8* %tmp) nounwind, !clang.arc.copy_on_escape !0 + store i8* %tmp2, i8** %z + tail call void @use_pointer(i8* %tmp2) + tail call void @use_pointer(i8* %tmp2) + tail call void @objc_release(i8* %tmp2) nounwind, !clang.imprecise_release !0 + tail call void @objc_release(i8* %tmp) nounwind, !clang.imprecise_release !0 + ret void +}