Extend CaptureTracking to indicate when a value is never stored, even
if it is not ultimately captured. Teach BasicAliasAnalysis that a local object address which does not escape and is never stored does not alias with a value resulting from a load. llvm-svn: 89398
This commit is contained in:
Dan Gohman
parent
b6c7704a8d
commit
94e617627d
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@ -21,8 +21,12 @@ namespace llvm {
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/// by the enclosing function (which is required to exist). This routine can
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/// be expensive, so consider caching the results. The boolean ReturnCaptures
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/// specifies whether returning the value (or part of it) from the function
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/// counts as capturing it or not. The boolean StoreCaptures specified whether
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/// storing the value (or part of it) into memory anywhere automatically
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/// counts as capturing it or not.
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bool PointerMayBeCaptured(const Value *V, bool ReturnCaptures);
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bool PointerMayBeCaptured(const Value *V,
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bool ReturnCaptures,
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bool StoreCaptures);
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} // end namespace llvm
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@ -79,7 +79,12 @@ static bool isKnownNonNull(const Value *V) {
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static bool isNonEscapingLocalObject(const Value *V) {
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// If this is a local allocation, check to see if it escapes.
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if (isa<AllocaInst>(V) || isNoAliasCall(V))
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return !PointerMayBeCaptured(V, false);
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// Set StoreCaptures to True so that we can assume in our callers that the
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// pointer is not the result of a load instruction. Currently
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// PointerMayBeCaptured doesn't have any special analysis for the
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// StoreCaptures=false case; if it did, our callers could be refined to be
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// more precise.
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return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
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// If this is an argument that corresponds to a byval or noalias argument,
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// then it has not escaped before entering the function. Check if it escapes
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@ -89,7 +94,7 @@ static bool isNonEscapingLocalObject(const Value *V) {
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// Don't bother analyzing arguments already known not to escape.
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if (A->hasNoCaptureAttr())
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return true;
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return !PointerMayBeCaptured(V, false);
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return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
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}
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return false;
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}
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@ -683,15 +688,19 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
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(V2Size != ~0U && isObjectSmallerThan(O1, V2Size, *TD)))
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return NoAlias;
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// If one pointer is the result of a call/invoke and the other is a
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// If one pointer is the result of a call/invoke or load and the other is a
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// non-escaping local object, then we know the object couldn't escape to a
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// point where the call could return it.
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if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
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isNonEscapingLocalObject(O2) && O1 != O2)
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return NoAlias;
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if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
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isNonEscapingLocalObject(O1) && O1 != O2)
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return NoAlias;
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// point where the call could return it. The load case works because
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// isNonEscapingLocalObject considers all stores to be escapes (it
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// passes true for the StoreCaptures argument to PointerMayBeCaptured).
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if (O1 != O2) {
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if ((isa<CallInst>(O1) || isa<InvokeInst>(O1) || isa<LoadInst>(O1)) &&
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isNonEscapingLocalObject(O2))
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return NoAlias;
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if ((isa<CallInst>(O2) || isa<InvokeInst>(O2) || isa<LoadInst>(O2)) &&
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isNonEscapingLocalObject(O1))
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return NoAlias;
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}
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if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
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std::swap(V1, V2);
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@ -28,8 +28,11 @@ using namespace llvm;
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/// by the enclosing function (which is required to exist). This routine can
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/// be expensive, so consider caching the results. The boolean ReturnCaptures
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/// specifies whether returning the value (or part of it) from the function
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/// counts as capturing it or not. The boolean StoreCaptures specified whether
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/// storing the value (or part of it) into memory anywhere automatically
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/// counts as capturing it or not.
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bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
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bool llvm::PointerMayBeCaptured(const Value *V,
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bool ReturnCaptures, bool StoreCaptures) {
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assert(isa<PointerType>(V->getType()) && "Capture is for pointers only!");
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SmallVector<Use*, 16> Worklist;
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SmallSet<Use*, 16> Visited;
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@ -82,7 +85,11 @@ bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
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break;
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case Instruction::Store:
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if (V == I->getOperand(0))
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// Stored the pointer - it may be captured.
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// Stored the pointer - conservatively assume it may be captured.
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// TODO: If StoreCaptures is not true, we could do Fancy analysis
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// to determine whether this store is not actually an escape point.
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// In that case, BasicAliasAnalysis should be updated as well to
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// take advantage of this.
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return true;
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// Storing to the pointee does not cause the pointer to be captured.
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break;
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@ -212,7 +212,7 @@ bool FunctionAttrs::AddNoCaptureAttrs(const std::vector<CallGraphNode *> &SCC) {
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for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A!=E; ++A)
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if (isa<PointerType>(A->getType()) && !A->hasNoCaptureAttr() &&
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!PointerMayBeCaptured(A, true)) {
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!PointerMayBeCaptured(A, true, /*StoreCaptures=*/false)) {
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A->addAttr(Attribute::NoCapture);
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++NumNoCapture;
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Changed = true;
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@ -280,7 +280,7 @@ bool FunctionAttrs::IsFunctionMallocLike(Function *F,
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return false; // Did not come from an allocation.
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}
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if (PointerMayBeCaptured(RetVal, false))
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if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
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return false;
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}
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@ -0,0 +1,108 @@
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; RUN: opt < %s -gvn -stats |& grep {Number of loads deleted}
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; rdar://7363102
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; GVN should be able to eliminate load %tmp22.i, because it is redundant with
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; load %tmp8.i. This requires being able to prove that %tmp7.i doesn't
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; alias the malloc'd value %tmp.i20.i.i, which it can do since %tmp7.i
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; is derived from %tmp5.i which is computed from a load, and %tmp.i20.i.i
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; is never stored and does not escape.
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
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target triple = "x86_64-apple-darwin10.0"
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%"struct.llvm::MallocAllocator" = type <{ i8 }>
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%"struct.llvm::StringMap<void*,llvm::MallocAllocator>" = type { %"struct.llvm::StringMapImpl", %"struct.llvm::MallocAllocator" }
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%"struct.llvm::StringMapEntry<void*>" = type { %"struct.llvm::StringMapEntryBase", i8* }
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%"struct.llvm::StringMapEntryBase" = type { i32 }
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%"struct.llvm::StringMapImpl" = type { %"struct.llvm::StringMapImpl::ItemBucket"*, i32, i32, i32, i32 }
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%"struct.llvm::StringMapImpl::ItemBucket" = type { i32, %"struct.llvm::StringMapEntryBase"* }
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%"struct.llvm::StringRef" = type { i8*, i64 }
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define %"struct.llvm::StringMapEntry<void*>"* @_Z3fooRN4llvm9StringMapIPvNS_15MallocAllocatorEEEPKc(%"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %X, i8* %P) ssp {
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entry:
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%tmp = alloca %"struct.llvm::StringRef", align 8 ; <%"struct.llvm::StringRef"*> [#uses=3]
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%tmp.i = getelementptr inbounds %"struct.llvm::StringRef"* %tmp, i64 0, i32 0 ; <i8**> [#uses=1]
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store i8* %P, i8** %tmp.i, align 8
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%tmp1.i = call i64 @strlen(i8* %P) nounwind readonly ; <i64> [#uses=1]
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%tmp2.i = getelementptr inbounds %"struct.llvm::StringRef"* %tmp, i64 0, i32 1 ; <i64*> [#uses=1]
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store i64 %tmp1.i, i64* %tmp2.i, align 8
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%tmp1 = call %"struct.llvm::StringMapEntry<void*>"* @_ZN4llvm9StringMapIPvNS_15MallocAllocatorEE16GetOrCreateValueERKNS_9StringRefE(%"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %X, %"struct.llvm::StringRef"* %tmp) ssp ; <%"struct.llvm::StringMapEntry<void*>"*> [#uses=1]
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ret %"struct.llvm::StringMapEntry<void*>"* %tmp1
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}
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declare i64 @strlen(i8* nocapture) nounwind readonly
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declare noalias i8* @malloc(i64) nounwind
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declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32) nounwind
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declare i32 @_ZN4llvm13StringMapImpl15LookupBucketForENS_9StringRefE(%"struct.llvm::StringMapImpl"*, i64, i64)
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define linkonce_odr %"struct.llvm::StringMapEntry<void*>"* @_ZN4llvm9StringMapIPvNS_15MallocAllocatorEE16GetOrCreateValueERKNS_9StringRefE(%"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %this, %"struct.llvm::StringRef"* nocapture %Key) ssp align 2 {
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entry:
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%elt = bitcast %"struct.llvm::StringRef"* %Key to i64* ; <i64*> [#uses=1]
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%val = load i64* %elt ; <i64> [#uses=3]
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%tmp = getelementptr inbounds %"struct.llvm::StringRef"* %Key, i64 0, i32 1 ; <i64*> [#uses=1]
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%val2 = load i64* %tmp ; <i64> [#uses=2]
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%tmp2.i = getelementptr inbounds %"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %this, i64 0, i32 0 ; <%"struct.llvm::StringMapImpl"*> [#uses=1]
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%tmp3.i = tail call i32 @_ZN4llvm13StringMapImpl15LookupBucketForENS_9StringRefE(%"struct.llvm::StringMapImpl"* %tmp2.i, i64 %val, i64 %val2) ; <i32> [#uses=1]
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%tmp4.i = getelementptr inbounds %"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %this, i64 0, i32 0, i32 0 ; <%"struct.llvm::StringMapImpl::ItemBucket"**> [#uses=1]
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%tmp5.i = load %"struct.llvm::StringMapImpl::ItemBucket"** %tmp4.i, align 8 ; <%"struct.llvm::StringMapImpl::ItemBucket"*> [#uses=1]
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%tmp6.i = zext i32 %tmp3.i to i64 ; <i64> [#uses=1]
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%tmp7.i = getelementptr inbounds %"struct.llvm::StringMapImpl::ItemBucket"* %tmp5.i, i64 %tmp6.i, i32 1 ; <%"struct.llvm::StringMapEntryBase"**> [#uses=2]
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%tmp8.i = load %"struct.llvm::StringMapEntryBase"** %tmp7.i, align 8 ; <%"struct.llvm::StringMapEntryBase"*> [#uses=3]
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%tmp9.i = icmp eq %"struct.llvm::StringMapEntryBase"* %tmp8.i, null ; <i1> [#uses=1]
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%tmp13.i = icmp eq %"struct.llvm::StringMapEntryBase"* %tmp8.i, inttoptr (i64 -1 to %"struct.llvm::StringMapEntryBase"*) ; <i1> [#uses=1]
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%or.cond.i = or i1 %tmp9.i, %tmp13.i ; <i1> [#uses=1]
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br i1 %or.cond.i, label %bb4.i, label %bb6.i
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bb4.i: ; preds = %entry
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%tmp41.i = inttoptr i64 %val to i8* ; <i8*> [#uses=2]
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%tmp4.i35.i = getelementptr inbounds i8* %tmp41.i, i64 %val2 ; <i8*> [#uses=1]
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%tmp.i.i = ptrtoint i8* %tmp4.i35.i to i64 ; <i64> [#uses=1]
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%tmp1.i.i = trunc i64 %tmp.i.i to i32 ; <i32> [#uses=1]
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%tmp3.i.i = trunc i64 %val to i32 ; <i32> [#uses=1]
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%tmp4.i.i = sub i32 %tmp1.i.i, %tmp3.i.i ; <i32> [#uses=3]
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%tmp5.i.i = add i32 %tmp4.i.i, 17 ; <i32> [#uses=1]
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%tmp8.i.i = zext i32 %tmp5.i.i to i64 ; <i64> [#uses=1]
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%tmp.i20.i.i = tail call noalias i8* @malloc(i64 %tmp8.i.i) nounwind ; <i8*> [#uses=7]
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%tmp10.i.i = bitcast i8* %tmp.i20.i.i to %"struct.llvm::StringMapEntry<void*>"* ; <%"struct.llvm::StringMapEntry<void*>"*> [#uses=2]
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%tmp12.i.i = icmp eq i8* %tmp.i20.i.i, null ; <i1> [#uses=1]
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br i1 %tmp12.i.i, label %_ZN4llvm14StringMapEntryIPvE6CreateINS_15MallocAllocatorES1_EEPS2_PKcS7_RT_T0_.exit.i, label %bb.i.i
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bb.i.i: ; preds = %bb4.i
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%tmp.i.i.i.i = bitcast i8* %tmp.i20.i.i to i32* ; <i32*> [#uses=1]
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store i32 %tmp4.i.i, i32* %tmp.i.i.i.i, align 4
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%tmp1.i19.i.i = getelementptr inbounds i8* %tmp.i20.i.i, i64 8 ; <i8*> [#uses=1]
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%0 = bitcast i8* %tmp1.i19.i.i to i8** ; <i8**> [#uses=1]
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store i8* null, i8** %0, align 8
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br label %_ZN4llvm14StringMapEntryIPvE6CreateINS_15MallocAllocatorES1_EEPS2_PKcS7_RT_T0_.exit.i
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_ZN4llvm14StringMapEntryIPvE6CreateINS_15MallocAllocatorES1_EEPS2_PKcS7_RT_T0_.exit.i: ; preds = %bb4.i, %bb.i.i
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%tmp.i18.i.i = getelementptr inbounds i8* %tmp.i20.i.i, i64 16 ; <i8*> [#uses=1]
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%tmp15.i.i = zext i32 %tmp4.i.i to i64 ; <i64> [#uses=2]
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tail call void @llvm.memcpy.i64(i8* %tmp.i18.i.i, i8* %tmp41.i, i64 %tmp15.i.i, i32 1) nounwind
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%tmp.i18.sum.i.i = add i64 %tmp15.i.i, 16 ; <i64> [#uses=1]
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%tmp17.i.i = getelementptr inbounds i8* %tmp.i20.i.i, i64 %tmp.i18.sum.i.i ; <i8*> [#uses=1]
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store i8 0, i8* %tmp17.i.i, align 1
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%tmp.i.i.i = getelementptr inbounds i8* %tmp.i20.i.i, i64 8 ; <i8*> [#uses=1]
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%1 = bitcast i8* %tmp.i.i.i to i8** ; <i8**> [#uses=1]
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store i8* null, i8** %1, align 8
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%tmp22.i = load %"struct.llvm::StringMapEntryBase"** %tmp7.i, align 8 ; <%"struct.llvm::StringMapEntryBase"*> [#uses=1]
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%tmp24.i = icmp eq %"struct.llvm::StringMapEntryBase"* %tmp22.i, inttoptr (i64 -1 to %"struct.llvm::StringMapEntryBase"*) ; <i1> [#uses=1]
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br i1 %tmp24.i, label %bb9.i, label %_ZN4llvm9StringMapIPvNS_15MallocAllocatorEE16GetOrCreateValueIS1_EERNS_14StringMapEntryIS1_EENS_9StringRefET_.exit
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bb6.i: ; preds = %entry
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%tmp16.i = bitcast %"struct.llvm::StringMapEntryBase"* %tmp8.i to %"struct.llvm::StringMapEntry<void*>"* ; <%"struct.llvm::StringMapEntry<void*>"*> [#uses=1]
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ret %"struct.llvm::StringMapEntry<void*>"* %tmp16.i
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bb9.i: ; preds = %_ZN4llvm14StringMapEntryIPvE6CreateINS_15MallocAllocatorES1_EEPS2_PKcS7_RT_T0_.exit.i
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%tmp25.i = getelementptr inbounds %"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %this, i64 0, i32 0, i32 3 ; <i32*> [#uses=2]
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%tmp26.i = load i32* %tmp25.i, align 8 ; <i32> [#uses=1]
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%tmp27.i = add i32 %tmp26.i, -1 ; <i32> [#uses=1]
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store i32 %tmp27.i, i32* %tmp25.i, align 8
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ret %"struct.llvm::StringMapEntry<void*>"* %tmp10.i.i
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_ZN4llvm9StringMapIPvNS_15MallocAllocatorEE16GetOrCreateValueIS1_EERNS_14StringMapEntryIS1_EENS_9StringRefET_.exit: ; preds = %_ZN4llvm14StringMapEntryIPvE6CreateINS_15MallocAllocatorES1_EEPS2_PKcS7_RT_T0_.exit.i
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ret %"struct.llvm::StringMapEntry<void*>"* %tmp10.i.i
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}
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