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Make provenance checking conservative in cases when

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pointers-to-strong-pointers may be in play. These can lead to retains and
releases happening in unstructured ways, foiling the optimizer. This fixes
rdar://12150909.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163180 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2012-09-04 23:16:20 +00:00
parent be11991208
commit 230768bd13
4 changed files with 126 additions and 47 deletions
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5
include/llvm/Analysis/AliasAnalysis.h
View File

@ -194,6 +194,11 @@ public:
return isNoAlias(Location(V1, V1Size), Location(V2, V2Size));
}
/// isNoAlias - A convenience wrapper.
bool isNoAlias(const Value *V1, const Value *V2) {
return isNoAlias(Location(V1), Location(V2));
}
/// isMustAlias - A convenience wrapper.
bool isMustAlias(const Location &LocA, const Location &LocB) {
return alias(LocA, LocB) == MustAlias;

79
lib/Transforms/Scalar/ObjCARC.cpp
View File

@ -1236,16 +1236,19 @@ bool ProvenanceAnalysis::relatedCheck(const Value *A, const Value *B) {
// An ObjC-Identified object can't alias a load if it is never locally stored.
if (AIsIdentified) {
// Check for an obvious escape.
if (isa<LoadInst>(B))
return isStoredObjCPointer(A);
if (BIsIdentified) {
// If both pointers have provenance, they can be directly compared.
if (A != B)
return false;
} else {
if (isa<LoadInst>(B))
return isStoredObjCPointer(A);
// Check for an obvious escape.
if (isa<LoadInst>(A))
return isStoredObjCPointer(B);
// Both pointers are identified and escapes aren't an evident problem.
return false;
}
} else {
if (BIsIdentified && isa<LoadInst>(A))
} else if (BIsIdentified) {
// Check for an obvious escape.
if (isa<LoadInst>(A))
return isStoredObjCPointer(B);
}
@ -1381,9 +1384,6 @@ namespace {
/// PtrState - This class summarizes several per-pointer runtime properties
/// which are propogated through the flow graph.
class PtrState {
/// NestCount - The known minimum level of retain+release nesting.
unsigned NestCount;
/// KnownPositiveRefCount - True if the reference count is known to
/// be incremented.
bool KnownPositiveRefCount;
@ -1401,7 +1401,7 @@ namespace {
/// TODO: Encapsulate this better.
RRInfo RRI;
PtrState() : NestCount(0), KnownPositiveRefCount(false), Partial(false),
PtrState() : KnownPositiveRefCount(false), Partial(false),
Seq(S_None) {}
void SetKnownPositiveRefCount() {
@ -1416,18 +1416,6 @@ namespace {
return KnownPositiveRefCount;
}
void IncrementNestCount() {
if (NestCount != UINT_MAX) ++NestCount;
}
void DecrementNestCount() {
if (NestCount != 0) --NestCount;
}
bool IsKnownNested() const {
return NestCount > 0;
}
void SetSeq(Sequence NewSeq) {
Seq = NewSeq;
}
@ -1454,7 +1442,6 @@ void
PtrState::Merge(const PtrState &Other, bool TopDown) {
Seq = MergeSeqs(Seq, Other.Seq, TopDown);
KnownPositiveRefCount = KnownPositiveRefCount && Other.KnownPositiveRefCount;
NestCount = std::min(NestCount, Other.NestCount);
// We can't merge a plain objc_retain with an objc_retainBlock.
if (RRI.IsRetainBlock != Other.RRI.IsRetainBlock)
@ -1868,6 +1855,26 @@ Constant *ObjCARCOpt::getAutoreleaseCallee(Module *M) {
return AutoreleaseCallee;
}
/// IsPotentialUse - Test whether the given value is possible a
/// reference-counted pointer, including tests which utilize AliasAnalysis.
static bool IsPotentialUse(const Value *Op, AliasAnalysis &AA) {
// First make the rudimentary check.
if (!IsPotentialUse(Op))
return false;
// Objects in constant memory are not reference-counted.
if (AA.pointsToConstantMemory(Op))
return false;
// Pointers in constant memory are not pointing to reference-counted objects.
if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
if (AA.pointsToConstantMemory(LI->getPointerOperand()))
return false;
// Otherwise assume the worst.
return true;
}
/// CanAlterRefCount - Test whether the given instruction can result in a
/// reference count modification (positive or negative) for the pointer's
/// object.
@ -1894,7 +1901,7 @@ CanAlterRefCount(const Instruction *Inst, const Value *Ptr,
for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
I != E; ++I) {
const Value *Op = *I;
if (IsPotentialUse(Op) && PA.related(Ptr, Op))
if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
return true;
}
return false;
@ -1919,14 +1926,14 @@ CanUse(const Instruction *Inst, const Value *Ptr, ProvenanceAnalysis &PA,
// Comparing a pointer with null, or any other constant, isn't really a use,
// because we don't care what the pointer points to, or about the values
// of any other dynamic reference-counted pointers.
if (!IsPotentialUse(ICI->getOperand(1)))
if (!IsPotentialUse(ICI->getOperand(1), *PA.getAA()))
return false;
} else if (ImmutableCallSite CS = static_cast<const Value *>(Inst)) {
// For calls, just check the arguments (and not the callee operand).
for (ImmutableCallSite::arg_iterator OI = CS.arg_begin(),
OE = CS.arg_end(); OI != OE; ++OI) {
const Value *Op = *OI;
if (IsPotentialUse(Op) && PA.related(Ptr, Op))
if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
return true;
}
return false;
@ -1936,14 +1943,14 @@ CanUse(const Instruction *Inst, const Value *Ptr, ProvenanceAnalysis &PA,
const Value *Op = GetUnderlyingObjCPtr(SI->getPointerOperand());
// If we can't tell what the underlying object was, assume there is a
// dependence.
return IsPotentialUse(Op) && PA.related(Op, Ptr);
return IsPotentialUse(Op, *PA.getAA()) && PA.related(Op, Ptr);
}
// Check each operand for a match.
for (User::const_op_iterator OI = Inst->op_begin(), OE = Inst->op_end();
OI != OE; ++OI) {
const Value *Op = *OI;
if (IsPotentialUse(Op) && PA.related(Ptr, Op))
if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
return true;
}
return false;
@ -2612,11 +2619,11 @@ ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst,
MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
S.ResetSequenceProgress(ReleaseMetadata ? S_MovableRelease : S_Release);
S.RRI.ReleaseMetadata = ReleaseMetadata;
S.RRI.KnownSafe = S.IsKnownNested() || S.IsKnownIncremented();
S.RRI.KnownSafe = S.IsKnownIncremented();
S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
S.RRI.Calls.insert(Inst);
S.IncrementNestCount();
S.SetKnownPositiveRefCount();
break;
}
case IC_RetainBlock:
@ -2631,7 +2638,6 @@ ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst,
PtrState &S = MyStates.getPtrBottomUpState(Arg);
S.SetKnownPositiveRefCount();
S.DecrementNestCount();
switch (S.GetSeq()) {
case S_Stop:
@ -2823,12 +2829,11 @@ ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
S.ResetSequenceProgress(S_Retain);
S.RRI.IsRetainBlock = Class == IC_RetainBlock;
// Don't check S.IsKnownIncremented() here because it's not sufficient.
S.RRI.KnownSafe = S.IsKnownNested();
S.RRI.KnownSafe = S.IsKnownIncremented();
S.RRI.Calls.insert(Inst);
}
S.IncrementNestCount();
S.SetKnownPositiveRefCount();
// A retain can be a potential use; procede to the generic checking
// code below.
@ -2838,7 +2843,7 @@ ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
Arg = GetObjCArg(Inst);
PtrState &S = MyStates.getPtrTopDownState(Arg);
S.DecrementNestCount();
S.ClearRefCount();
switch (S.GetSeq()) {
case S_Retain:

4
test/Transforms/ObjCARC/basic.ll
View File

@ -1,4 +1,4 @@
; RUN: opt -objc-arc -S < %s | FileCheck %s
; RUN: opt -basicaa -objc-arc -S < %s | FileCheck %s
target datalayout = "e-p:64:64:64"
@ -1498,7 +1498,7 @@ define i8* @test49(i8* %p) nounwind {
}
; Do delete retain+release with intervening stores of the
; address value;
; address value.
; CHECK: define void @test50(
; CHECK-NOT: @objc_

85
test/Transforms/ObjCARC/nested.ll
View File

@ -16,6 +16,10 @@ declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind
declare i8* @objc_msgSend(i8*, i8*, ...) nonlazybind
declare void @use(i8*)
declare void @objc_release(i8*)
declare i8* @def()
declare void @__crasher_block_invoke(i8* nocapture)
declare i8* @objc_retainBlock(i8*)
declare void @__crasher_block_invoke1(i8* nocapture)
!0 = metadata !{}
@ -279,11 +283,13 @@ forcoll.empty:
ret void
}
; Delete a nested retain+release pair.
; TODO: Delete a nested retain+release pair.
; The optimizer currently can't do this, because isn't isn't sophisticated enough in
; reasnoning about nesting.
; CHECK: define void @test6(
; CHECK: call i8* @objc_retain
; CHECK-NOT: @objc_retain
; CHECK: @objc_retain
; CHECK: }
define void @test6() nounwind {
entry:
@ -345,11 +351,13 @@ forcoll.empty:
ret void
}
; Delete a nested retain+release pair.
; TODO: Delete a nested retain+release pair.
; The optimizer currently can't do this, because isn't isn't sophisticated enough in
; reasnoning about nesting.
; CHECK: define void @test7(
; CHECK: call i8* @objc_retain
; CHECK-NOT: @objc_retain
; CHECK: @objc_retain
; CHECK: }
define void @test7() nounwind {
entry:
@ -553,12 +561,12 @@ forcoll.empty:
ret void
}
; Like test9, but without a split backedge. This we can optimize.
; Like test9, but without a split backedge. TODO: optimize this.
; CHECK: define void @test9b(
; CHECK: call i8* @objc_retain
; CHECK: call i8* @objc_retain
; CHECK-NOT: @objc_retain
; CHECK: @objc_retain
; CHECK: }
define void @test9b() nounwind {
entry:
@ -687,12 +695,12 @@ forcoll.empty:
ret void
}
; Like test10, but without a split backedge. This we can optimize.
; Like test10, but without a split backedge. TODO: optimize this.
; CHECK: define void @test10b(
; CHECK: call i8* @objc_retain
; CHECK: call i8* @objc_retain
; CHECK-NOT: @objc_retain
; CHECK: @objc_retain
; CHECK: }
define void @test10b() nounwind {
entry:
@ -751,3 +759,64 @@ forcoll.empty:
call void @objc_release(i8* %0) nounwind, !clang.imprecise_release !0
ret void
}
; Pointers to strong pointers can obscure provenance relationships. Be conservative
; in the face of escaping pointers. rdar://12150909.
%struct.__block_d = type { i64, i64 }
@_NSConcreteStackBlock = external global i8*
@__block_d_tmp = external hidden constant { i64, i64, i8*, i8*, i8*, i8* }
@__block_d_tmp5 = external hidden constant { i64, i64, i8*, i8*, i8*, i8* }
; CHECK: define void @test11(
; CHECK: tail call i8* @objc_retain(i8* %call) nounwind
; CHECK: tail call i8* @objc_retain(i8* %call) nounwind
; CHECK: call void @objc_release(i8* %call) nounwind, !clang.imprecise_release !0
; CHECK: }
define void @test11() {
entry:
%block = alloca <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>, align 8
%block9 = alloca <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>, align 8
%call = call i8* @def(), !clang.arc.no_objc_arc_exceptions !0
%foo = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block, i64 0, i32 5
%block.isa = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block, i64 0, i32 0
store i8* bitcast (i8** @_NSConcreteStackBlock to i8*), i8** %block.isa, align 8
%block.flags = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block, i64 0, i32 1
store i32 1107296256, i32* %block.flags, align 8
%block.reserved = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block, i64 0, i32 2
store i32 0, i32* %block.reserved, align 4
%block.invoke = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block, i64 0, i32 3
store i8* bitcast (void (i8*)* @__crasher_block_invoke to i8*), i8** %block.invoke, align 8
%block.d = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block, i64 0, i32 4
store %struct.__block_d* bitcast ({ i64, i64, i8*, i8*, i8*, i8* }* @__block_d_tmp to %struct.__block_d*), %struct.__block_d** %block.d, align 8
%foo2 = tail call i8* @objc_retain(i8* %call) nounwind
store i8* %foo2, i8** %foo, align 8
%foo4 = bitcast <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block to i8*
%foo5 = call i8* @objc_retainBlock(i8* %foo4) nounwind
call void @use(i8* %foo5), !clang.arc.no_objc_arc_exceptions !0
call void @objc_release(i8* %foo5) nounwind
%strongdestroy = load i8** %foo, align 8
call void @objc_release(i8* %strongdestroy) nounwind, !clang.imprecise_release !0
%foo10 = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block9, i64 0, i32 5
%block.isa11 = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block9, i64 0, i32 0
store i8* bitcast (i8** @_NSConcreteStackBlock to i8*), i8** %block.isa11, align 8
%block.flags12 = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block9, i64 0, i32 1
store i32 1107296256, i32* %block.flags12, align 8
%block.reserved13 = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block9, i64 0, i32 2
store i32 0, i32* %block.reserved13, align 4
%block.invoke14 = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block9, i64 0, i32 3
store i8* bitcast (void (i8*)* @__crasher_block_invoke1 to i8*), i8** %block.invoke14, align 8
%block.d15 = getelementptr inbounds <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block9, i64 0, i32 4
store %struct.__block_d* bitcast ({ i64, i64, i8*, i8*, i8*, i8* }* @__block_d_tmp5 to %struct.__block_d*), %struct.__block_d** %block.d15, align 8
%foo18 = call i8* @objc_retain(i8* %call) nounwind
store i8* %call, i8** %foo10, align 8
%foo20 = bitcast <{ i8*, i32, i32, i8*, %struct.__block_d*, i8* }>* %block9 to i8*
%foo21 = call i8* @objc_retainBlock(i8* %foo20) nounwind
call void @use(i8* %foo21), !clang.arc.no_objc_arc_exceptions !0
call void @objc_release(i8* %foo21) nounwind
%strongdestroy25 = load i8** %foo10, align 8
call void @objc_release(i8* %strongdestroy25) nounwind, !clang.imprecise_release !0
call void @objc_release(i8* %call) nounwind, !clang.imprecise_release !0
ret void
}