X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FTypeBasedAliasAnalysis.cpp;h=115872584cb298b1d076630f89eea8d1058872a6;hb=c16fc548515f2fd01bc2cbe4befd822a636cc154;hp=8d368470b4e4e365971219cbe15b076dc944d585;hpb=acf50f5136c6f1daca2e78db756514a88470516b;p=oota-llvm.git diff --git a/lib/Analysis/TypeBasedAliasAnalysis.cpp b/lib/Analysis/TypeBasedAliasAnalysis.cpp index 8d368470b4e..115872584cb 100644 --- a/lib/Analysis/TypeBasedAliasAnalysis.cpp +++ b/lib/Analysis/TypeBasedAliasAnalysis.cpp @@ -12,28 +12,131 @@ // // In LLVM IR, memory does not have types, so LLVM's own type system is not // suitable for doing TBAA. Instead, metadata is added to the IR to describe -// a type system of a higher level language. +// a type system of a higher level language. This can be used to implement +// typical C/C++ TBAA, but it can also be used to implement custom alias +// analysis behavior for other languages. // -// This pass is language-independent. The type system is encoded in -// metadata. This allows this pass to support typical C and C++ TBAA, but -// it can also support custom aliasing behavior for other languages. +// We now support two types of metadata format: scalar TBAA and struct-path +// aware TBAA. After all testing cases are upgraded to use struct-path aware +// TBAA and we can auto-upgrade existing bc files, the support for scalar TBAA +// can be dropped. // -// This is a work-in-progress. It doesn't work yet, and the metadata -// format isn't stable. +// The scalar TBAA metadata format is very simple. TBAA MDNodes have up to +// three fields, e.g.: +// !0 = metadata !{ metadata !"an example type tree" } +// !1 = metadata !{ metadata !"int", metadata !0 } +// !2 = metadata !{ metadata !"float", metadata !0 } +// !3 = metadata !{ metadata !"const float", metadata !2, i64 1 } // -// TODO: getModRefBehavior. The AliasAnalysis infrastructure will need to -// be extended. -// TODO: struct fields +// The first field is an identity field. It can be any value, usually +// an MDString, which uniquely identifies the type. The most important +// name in the tree is the name of the root node. Two trees with +// different root node names are entirely disjoint, even if they +// have leaves with common names. +// +// The second field identifies the type's parent node in the tree, or +// is null or omitted for a root node. A type is considered to alias +// all of its descendants and all of its ancestors in the tree. Also, +// a type is considered to alias all types in other trees, so that +// bitcode produced from multiple front-ends is handled conservatively. +// +// If the third field is present, it's an integer which if equal to 1 +// indicates that the type is "constant" (meaning pointsToConstantMemory +// should return true; see +// http://llvm.org/docs/AliasAnalysis.html#OtherItfs). +// +// With struct-path aware TBAA, the MDNodes attached to an instruction using +// "!tbaa" are called path tag nodes. +// +// The path tag node has 4 fields with the last field being optional. +// +// The first field is the base type node, it can be a struct type node +// or a scalar type node. The second field is the access type node, it +// must be a scalar type node. The third field is the offset into the base type. +// The last field has the same meaning as the last field of our scalar TBAA: +// it's an integer which if equal to 1 indicates that the access is "constant". +// +// The struct type node has a name and a list of pairs, one pair for each member +// of the struct. The first element of each pair is a type node (a struct type +// node or a sclar type node), specifying the type of the member, the second +// element of each pair is the offset of the member. +// +// Given an example +// typedef struct { +// short s; +// } A; +// typedef struct { +// uint16_t s; +// A a; +// } B; +// +// For an acess to B.a.s, we attach !5 (a path tag node) to the load/store +// instruction. The base type is !4 (struct B), the access type is !2 (scalar +// type short) and the offset is 4. +// +// !0 = metadata !{metadata !"Simple C/C++ TBAA"} +// !1 = metadata !{metadata !"omnipotent char", metadata !0} // Scalar type node +// !2 = metadata !{metadata !"short", metadata !1} // Scalar type node +// !3 = metadata !{metadata !"A", metadata !2, i64 0} // Struct type node +// !4 = metadata !{metadata !"B", metadata !2, i64 0, metadata !3, i64 4} +// // Struct type node +// !5 = metadata !{metadata !4, metadata !2, i64 4} // Path tag node +// +// The struct type nodes and the scalar type nodes form a type DAG. +// Root (!0) +// char (!1) -- edge to Root +// short (!2) -- edge to char +// A (!3) -- edge with offset 0 to short +// B (!4) -- edge with offset 0 to short and edge with offset 4 to A +// +// To check if two tags (tagX and tagY) can alias, we start from the base type +// of tagX, follow the edge with the correct offset in the type DAG and adjust +// the offset until we reach the base type of tagY or until we reach the Root +// node. +// If we reach the base type of tagY, compare the adjusted offset with +// offset of tagY, return Alias if the offsets are the same, return NoAlias +// otherwise. +// If we reach the Root node, perform the above starting from base type of tagY +// to see if we reach base type of tagX. +// +// If they have different roots, they're part of different potentially +// unrelated type systems, so we return Alias to be conservative. +// If neither node is an ancestor of the other and they have the same root, +// then we say NoAlias. +// +// TODO: The current metadata format doesn't support struct +// fields. For example: +// struct X { +// double d; +// int i; +// }; +// void foo(struct X *x, struct X *y, double *p) { +// *x = *y; +// *p = 0.0; +// } +// Struct X has a double member, so the store to *x can alias the store to *p. +// Currently it's not possible to precisely describe all the things struct X +// aliases, so struct assignments must use conservative TBAA nodes. There's +// no scheme for attaching metadata to @llvm.memcpy yet either. // //===----------------------------------------------------------------------===// -#include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/Passes.h" -#include "llvm/Module.h" -#include "llvm/Metadata.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Module.h" #include "llvm/Pass.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/ADT/SetVector.h" using namespace llvm; +// A handy option for disabling TBAA functionality. The same effect can also be +// achieved by stripping the !tbaa tags from IR, but this option is sometimes +// more convenient. +static cl::opt EnableTBAA("enable-tbaa", cl::init(true)); + namespace { /// TBAANode - This is a simple wrapper around an MDNode which provides a /// higher-level interface by hiding the details of how alias analysis @@ -42,13 +145,13 @@ namespace { const MDNode *Node; public: - TBAANode() : Node(0) {} + TBAANode() : Node(nullptr) {} explicit TBAANode(const MDNode *N) : Node(N) {} /// getNode - Get the MDNode for this TBAANode. const MDNode *getNode() const { return Node; } - /// getParent - Get this TBAANode's Alias DAG parent. + /// getParent - Get this TBAANode's Alias tree parent. TBAANode getParent() const { if (Node->getNumOperands() < 2) return TBAANode(); @@ -65,11 +168,106 @@ namespace { bool TypeIsImmutable() const { if (Node->getNumOperands() < 3) return false; - ConstantInt *CI = dyn_cast(Node->getOperand(2)); + ConstantInt *CI = mdconst::dyn_extract(Node->getOperand(2)); + if (!CI) + return false; + return CI->getValue()[0]; + } + }; + + /// This is a simple wrapper around an MDNode which provides a + /// higher-level interface by hiding the details of how alias analysis + /// information is encoded in its operands. + class TBAAStructTagNode { + /// This node should be created with createTBAAStructTagNode. + const MDNode *Node; + + public: + explicit TBAAStructTagNode(const MDNode *N) : Node(N) {} + + /// Get the MDNode for this TBAAStructTagNode. + const MDNode *getNode() const { return Node; } + + const MDNode *getBaseType() const { + return dyn_cast_or_null(Node->getOperand(0)); + } + const MDNode *getAccessType() const { + return dyn_cast_or_null(Node->getOperand(1)); + } + uint64_t getOffset() const { + return mdconst::extract(Node->getOperand(2))->getZExtValue(); + } + /// TypeIsImmutable - Test if this TBAAStructTagNode represents a type for + /// objects which are not modified (by any means) in the context where this + /// AliasAnalysis is relevant. + bool TypeIsImmutable() const { + if (Node->getNumOperands() < 4) + return false; + ConstantInt *CI = mdconst::dyn_extract(Node->getOperand(3)); if (!CI) return false; - // TODO: Think about the encoding. - return CI->isOne(); + return CI->getValue()[0]; + } + }; + + /// This is a simple wrapper around an MDNode which provides a + /// higher-level interface by hiding the details of how alias analysis + /// information is encoded in its operands. + class TBAAStructTypeNode { + /// This node should be created with createTBAAStructTypeNode. + const MDNode *Node; + + public: + TBAAStructTypeNode() : Node(nullptr) {} + explicit TBAAStructTypeNode(const MDNode *N) : Node(N) {} + + /// Get the MDNode for this TBAAStructTypeNode. + const MDNode *getNode() const { return Node; } + + /// Get this TBAAStructTypeNode's field in the type DAG with + /// given offset. Update the offset to be relative to the field type. + TBAAStructTypeNode getParent(uint64_t &Offset) const { + // Parent can be omitted for the root node. + if (Node->getNumOperands() < 2) + return TBAAStructTypeNode(); + + // Fast path for a scalar type node and a struct type node with a single + // field. + if (Node->getNumOperands() <= 3) { + uint64_t Cur = Node->getNumOperands() == 2 + ? 0 + : mdconst::extract(Node->getOperand(2)) + ->getZExtValue(); + Offset -= Cur; + MDNode *P = dyn_cast_or_null(Node->getOperand(1)); + if (!P) + return TBAAStructTypeNode(); + return TBAAStructTypeNode(P); + } + + // Assume the offsets are in order. We return the previous field if + // the current offset is bigger than the given offset. + unsigned TheIdx = 0; + for (unsigned Idx = 1; Idx < Node->getNumOperands(); Idx += 2) { + uint64_t Cur = mdconst::extract(Node->getOperand(Idx + 1)) + ->getZExtValue(); + if (Cur > Offset) { + assert(Idx >= 3 && + "TBAAStructTypeNode::getParent should have an offset match!"); + TheIdx = Idx - 2; + break; + } + } + // Move along the last field. + if (TheIdx == 0) + TheIdx = Node->getNumOperands() - 2; + uint64_t Cur = mdconst::extract(Node->getOperand(TheIdx + 1)) + ->getZExtValue(); + Offset -= Cur; + MDNode *P = dyn_cast_or_null(Node->getOperand(TheIdx)); + if (!P) + return TBAAStructTypeNode(); + return TBAAStructTypeNode(P); } }; } @@ -81,26 +279,35 @@ namespace { public AliasAnalysis { public: static char ID; // Class identification, replacement for typeinfo - TypeBasedAliasAnalysis() : ImmutablePass(ID) {} - - virtual void initializePass() { - InitializeAliasAnalysis(this); + TypeBasedAliasAnalysis() : ImmutablePass(ID) { + initializeTypeBasedAliasAnalysisPass(*PassRegistry::getPassRegistry()); } + bool doInitialization(Module &M) override; + /// getAdjustedAnalysisPointer - This method is used when a pass implements /// an analysis interface through multiple inheritance. If needed, it /// should override this to adjust the this pointer as needed for the /// specified pass info. - virtual void *getAdjustedAnalysisPointer(const void *PI) { + void *getAdjustedAnalysisPointer(const void *PI) override { if (PI == &AliasAnalysis::ID) return (AliasAnalysis*)this; return this; } + bool Aliases(const MDNode *A, const MDNode *B) const; + bool PathAliases(const MDNode *A, const MDNode *B) const; + private: - virtual void getAnalysisUsage(AnalysisUsage &AU) const; - virtual AliasResult alias(const Location &LocA, const Location &LocB); - virtual bool pointsToConstantMemory(const Location &Loc); + void getAnalysisUsage(AnalysisUsage &AU) const override; + AliasResult alias(const Location &LocA, const Location &LocB) override; + bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override; + ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override; + ModRefBehavior getModRefBehavior(const Function *F) override; + ModRefResult getModRefInfo(ImmutableCallSite CS, + const Location &Loc) override; + ModRefResult getModRefInfo(ImmutableCallSite CS1, + ImmutableCallSite CS2) override; }; } // End of anonymous namespace @@ -113,30 +320,43 @@ ImmutablePass *llvm::createTypeBasedAliasAnalysisPass() { return new TypeBasedAliasAnalysis(); } +bool TypeBasedAliasAnalysis::doInitialization(Module &M) { + InitializeAliasAnalysis(this, &M.getDataLayout()); + return true; +} + void TypeBasedAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); AliasAnalysis::getAnalysisUsage(AU); } -AliasAnalysis::AliasResult -TypeBasedAliasAnalysis::alias(const Location &LocA, - const Location &LocB) { - // Get the attached MDNodes. If either value lacks a tbaa MDNode, we must - // be conservative. - const MDNode *AM = LocA.TBAATag; - if (!AM) return AliasAnalysis::alias(LocA, LocB); - const MDNode *BM = LocB.TBAATag; - if (!BM) return AliasAnalysis::alias(LocA, LocB); +/// Check the first operand of the tbaa tag node, if it is a MDNode, we treat +/// it as struct-path aware TBAA format, otherwise, we treat it as scalar TBAA +/// format. +static bool isStructPathTBAA(const MDNode *MD) { + // Anonymous TBAA root starts with a MDNode and dragonegg uses it as + // a TBAA tag. + return isa(MD->getOperand(0)) && MD->getNumOperands() >= 3; +} + +/// Aliases - Test whether the type represented by A may alias the +/// type represented by B. +bool +TypeBasedAliasAnalysis::Aliases(const MDNode *A, + const MDNode *B) const { + // Make sure that both MDNodes are struct-path aware. + if (isStructPathTBAA(A) && isStructPathTBAA(B)) + return PathAliases(A, B); // Keep track of the root node for A and B. TBAANode RootA, RootB; - // Climb the DAG from A to see if we reach B. - for (TBAANode T(AM); ; ) { - if (T.getNode() == BM) + // Climb the tree from A to see if we reach B. + for (TBAANode T(A); ; ) { + if (T.getNode() == B) // B is an ancestor of A. - return AliasAnalysis::alias(LocA, LocB); + return true; RootA = T; T = T.getParent(); @@ -144,11 +364,11 @@ TypeBasedAliasAnalysis::alias(const Location &LocA, break; } - // Climb the DAG from B to see if we reach A. - for (TBAANode T(BM); ; ) { - if (T.getNode() == AM) + // Climb the tree from B to see if we reach A. + for (TBAANode T(B); ; ) { + if (T.getNode() == A) // A is an ancestor of B. - return AliasAnalysis::alias(LocA, LocB); + return true; RootB = T; T = T.getParent(); @@ -158,23 +378,268 @@ TypeBasedAliasAnalysis::alias(const Location &LocA, // Neither node is an ancestor of the other. + // If they have different roots, they're part of different potentially + // unrelated type systems, so we must be conservative. + if (RootA.getNode() != RootB.getNode()) + return true; + // If they have the same root, then we've proved there's no alias. - if (RootA.getNode() == RootB.getNode()) - return NoAlias; + return false; +} + +/// Test whether the struct-path tag represented by A may alias the +/// struct-path tag represented by B. +bool +TypeBasedAliasAnalysis::PathAliases(const MDNode *A, + const MDNode *B) const { + // Verify that both input nodes are struct-path aware. + assert(isStructPathTBAA(A) && "MDNode A is not struct-path aware."); + assert(isStructPathTBAA(B) && "MDNode B is not struct-path aware."); + + // Keep track of the root node for A and B. + TBAAStructTypeNode RootA, RootB; + TBAAStructTagNode TagA(A), TagB(B); + + // TODO: We need to check if AccessType of TagA encloses AccessType of + // TagB to support aggregate AccessType. If yes, return true. + + // Start from the base type of A, follow the edge with the correct offset in + // the type DAG and adjust the offset until we reach the base type of B or + // until we reach the Root node. + // Compare the adjusted offset once we have the same base. + + // Climb the type DAG from base type of A to see if we reach base type of B. + const MDNode *BaseA = TagA.getBaseType(); + const MDNode *BaseB = TagB.getBaseType(); + uint64_t OffsetA = TagA.getOffset(), OffsetB = TagB.getOffset(); + for (TBAAStructTypeNode T(BaseA); ; ) { + if (T.getNode() == BaseB) + // Base type of A encloses base type of B, check if the offsets match. + return OffsetA == OffsetB; + + RootA = T; + // Follow the edge with the correct offset, OffsetA will be adjusted to + // be relative to the field type. + T = T.getParent(OffsetA); + if (!T.getNode()) + break; + } + + // Reset OffsetA and climb the type DAG from base type of B to see if we reach + // base type of A. + OffsetA = TagA.getOffset(); + for (TBAAStructTypeNode T(BaseB); ; ) { + if (T.getNode() == BaseA) + // Base type of B encloses base type of A, check if the offsets match. + return OffsetA == OffsetB; + + RootB = T; + // Follow the edge with the correct offset, OffsetB will be adjusted to + // be relative to the field type. + T = T.getParent(OffsetB); + if (!T.getNode()) + break; + } + + // Neither node is an ancestor of the other. // If they have different roots, they're part of different potentially // unrelated type systems, so we must be conservative. - return AliasAnalysis::alias(LocA, LocB); + if (RootA.getNode() != RootB.getNode()) + return true; + + // If they have the same root, then we've proved there's no alias. + return false; +} + +AliasAnalysis::AliasResult +TypeBasedAliasAnalysis::alias(const Location &LocA, + const Location &LocB) { + if (!EnableTBAA) + return AliasAnalysis::alias(LocA, LocB); + + // Get the attached MDNodes. If either value lacks a tbaa MDNode, we must + // be conservative. + const MDNode *AM = LocA.AATags.TBAA; + if (!AM) return AliasAnalysis::alias(LocA, LocB); + const MDNode *BM = LocB.AATags.TBAA; + if (!BM) return AliasAnalysis::alias(LocA, LocB); + + // If they may alias, chain to the next AliasAnalysis. + if (Aliases(AM, BM)) + return AliasAnalysis::alias(LocA, LocB); + + // Otherwise return a definitive result. + return NoAlias; } -bool TypeBasedAliasAnalysis::pointsToConstantMemory(const Location &Loc) { - const MDNode *M = Loc.TBAATag; - if (!M) return false; +bool TypeBasedAliasAnalysis::pointsToConstantMemory(const Location &Loc, + bool OrLocal) { + if (!EnableTBAA) + return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); + + const MDNode *M = Loc.AATags.TBAA; + if (!M) return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); // If this is an "immutable" type, we can assume the pointer is pointing // to constant memory. - if (TBAANode(M).TypeIsImmutable()) + if ((!isStructPathTBAA(M) && TBAANode(M).TypeIsImmutable()) || + (isStructPathTBAA(M) && TBAAStructTagNode(M).TypeIsImmutable())) return true; - return AliasAnalysis::pointsToConstantMemory(Loc); + return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); +} + +AliasAnalysis::ModRefBehavior +TypeBasedAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { + if (!EnableTBAA) + return AliasAnalysis::getModRefBehavior(CS); + + ModRefBehavior Min = UnknownModRefBehavior; + + // If this is an "immutable" type, we can assume the call doesn't write + // to memory. + if (const MDNode *M = CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa)) + if ((!isStructPathTBAA(M) && TBAANode(M).TypeIsImmutable()) || + (isStructPathTBAA(M) && TBAAStructTagNode(M).TypeIsImmutable())) + Min = OnlyReadsMemory; + + return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min); +} + +AliasAnalysis::ModRefBehavior +TypeBasedAliasAnalysis::getModRefBehavior(const Function *F) { + // Functions don't have metadata. Just chain to the next implementation. + return AliasAnalysis::getModRefBehavior(F); +} + +AliasAnalysis::ModRefResult +TypeBasedAliasAnalysis::getModRefInfo(ImmutableCallSite CS, + const Location &Loc) { + if (!EnableTBAA) + return AliasAnalysis::getModRefInfo(CS, Loc); + + if (const MDNode *L = Loc.AATags.TBAA) + if (const MDNode *M = + CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa)) + if (!Aliases(L, M)) + return NoModRef; + + return AliasAnalysis::getModRefInfo(CS, Loc); +} + +AliasAnalysis::ModRefResult +TypeBasedAliasAnalysis::getModRefInfo(ImmutableCallSite CS1, + ImmutableCallSite CS2) { + if (!EnableTBAA) + return AliasAnalysis::getModRefInfo(CS1, CS2); + + if (const MDNode *M1 = + CS1.getInstruction()->getMetadata(LLVMContext::MD_tbaa)) + if (const MDNode *M2 = + CS2.getInstruction()->getMetadata(LLVMContext::MD_tbaa)) + if (!Aliases(M1, M2)) + return NoModRef; + + return AliasAnalysis::getModRefInfo(CS1, CS2); +} + +bool MDNode::isTBAAVtableAccess() const { + if (!isStructPathTBAA(this)) { + if (getNumOperands() < 1) return false; + if (MDString *Tag1 = dyn_cast(getOperand(0))) { + if (Tag1->getString() == "vtable pointer") return true; + } + return false; + } + + // For struct-path aware TBAA, we use the access type of the tag. + if (getNumOperands() < 2) return false; + MDNode *Tag = cast_or_null(getOperand(1)); + if (!Tag) return false; + if (MDString *Tag1 = dyn_cast(Tag->getOperand(0))) { + if (Tag1->getString() == "vtable pointer") return true; + } + return false; +} + +MDNode *MDNode::getMostGenericTBAA(MDNode *A, MDNode *B) { + if (!A || !B) + return nullptr; + + if (A == B) + return A; + + // For struct-path aware TBAA, we use the access type of the tag. + bool StructPath = isStructPathTBAA(A) && isStructPathTBAA(B); + if (StructPath) { + A = cast_or_null(A->getOperand(1)); + if (!A) return nullptr; + B = cast_or_null(B->getOperand(1)); + if (!B) return nullptr; + } + + SmallSetVector PathA; + MDNode *T = A; + while (T) { + if (PathA.count(T)) + report_fatal_error("Cycle found in TBAA metadata."); + PathA.insert(T); + T = T->getNumOperands() >= 2 ? cast_or_null(T->getOperand(1)) + : nullptr; + } + + SmallSetVector PathB; + T = B; + while (T) { + if (PathB.count(T)) + report_fatal_error("Cycle found in TBAA metadata."); + PathB.insert(T); + T = T->getNumOperands() >= 2 ? cast_or_null(T->getOperand(1)) + : nullptr; + } + + int IA = PathA.size() - 1; + int IB = PathB.size() - 1; + + MDNode *Ret = nullptr; + while (IA >= 0 && IB >=0) { + if (PathA[IA] == PathB[IB]) + Ret = PathA[IA]; + else + break; + --IA; + --IB; + } + if (!StructPath) + return Ret; + + if (!Ret) + return nullptr; + // We need to convert from a type node to a tag node. + Type *Int64 = IntegerType::get(A->getContext(), 64); + Metadata *Ops[3] = {Ret, Ret, + ConstantAsMetadata::get(ConstantInt::get(Int64, 0))}; + return MDNode::get(A->getContext(), Ops); } + +void Instruction::getAAMetadata(AAMDNodes &N, bool Merge) const { + if (Merge) + N.TBAA = + MDNode::getMostGenericTBAA(N.TBAA, getMetadata(LLVMContext::MD_tbaa)); + else + N.TBAA = getMetadata(LLVMContext::MD_tbaa); + + if (Merge) + N.Scope = MDNode::getMostGenericAliasScope( + N.Scope, getMetadata(LLVMContext::MD_alias_scope)); + else + N.Scope = getMetadata(LLVMContext::MD_alias_scope); + + if (Merge) + N.NoAlias = + MDNode::intersect(N.NoAlias, getMetadata(LLVMContext::MD_noalias)); + else + N.NoAlias = getMetadata(LLVMContext::MD_noalias); +} +