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https://github.com/RPCS3/llvm.git
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c94e896e67
Summary: Make enum ModRefInfo an enum class. Changes to ModRefInfo values should be done using inline wrappers. This should prevent future bit-wise opearations from being added, which can be more error-prone. Reviewers: sanjoy, dberlin, hfinkel, george.burgess.iv Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D40933 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320107 91177308-0d34-0410-b5e6-96231b3b80d8
609 lines
21 KiB
C++
609 lines
21 KiB
C++
//===- TypeBasedAliasAnalysis.cpp - Type-Based Alias Analysis -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the TypeBasedAliasAnalysis pass, which implements
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// metadata-based TBAA.
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//
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// In LLVM IR, memory does not have types, so LLVM's own type system is not
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// suitable for doing TBAA. Instead, metadata is added to the IR to describe
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// a type system of a higher level language. This can be used to implement
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// typical C/C++ TBAA, but it can also be used to implement custom alias
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// analysis behavior for other languages.
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//
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// We now support two types of metadata format: scalar TBAA and struct-path
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// aware TBAA. After all testing cases are upgraded to use struct-path aware
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// TBAA and we can auto-upgrade existing bc files, the support for scalar TBAA
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// can be dropped.
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//
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// The scalar TBAA metadata format is very simple. TBAA MDNodes have up to
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// three fields, e.g.:
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// !0 = !{ !"an example type tree" }
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// !1 = !{ !"int", !0 }
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// !2 = !{ !"float", !0 }
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// !3 = !{ !"const float", !2, i64 1 }
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//
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// The first field is an identity field. It can be any value, usually
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// an MDString, which uniquely identifies the type. The most important
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// name in the tree is the name of the root node. Two trees with
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// different root node names are entirely disjoint, even if they
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// have leaves with common names.
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//
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// The second field identifies the type's parent node in the tree, or
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// is null or omitted for a root node. A type is considered to alias
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// all of its descendants and all of its ancestors in the tree. Also,
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// a type is considered to alias all types in other trees, so that
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// bitcode produced from multiple front-ends is handled conservatively.
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//
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// If the third field is present, it's an integer which if equal to 1
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// indicates that the type is "constant" (meaning pointsToConstantMemory
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// should return true; see
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// http://llvm.org/docs/AliasAnalysis.html#OtherItfs).
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//
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// With struct-path aware TBAA, the MDNodes attached to an instruction using
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// "!tbaa" are called path tag nodes.
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//
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// The path tag node has 4 fields with the last field being optional.
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//
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// The first field is the base type node, it can be a struct type node
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// or a scalar type node. The second field is the access type node, it
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// must be a scalar type node. The third field is the offset into the base type.
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// The last field has the same meaning as the last field of our scalar TBAA:
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// it's an integer which if equal to 1 indicates that the access is "constant".
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//
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// The struct type node has a name and a list of pairs, one pair for each member
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// of the struct. The first element of each pair is a type node (a struct type
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// node or a scalar type node), specifying the type of the member, the second
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// element of each pair is the offset of the member.
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//
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// Given an example
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// typedef struct {
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// short s;
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// } A;
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// typedef struct {
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// uint16_t s;
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// A a;
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// } B;
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//
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// For an access to B.a.s, we attach !5 (a path tag node) to the load/store
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// instruction. The base type is !4 (struct B), the access type is !2 (scalar
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// type short) and the offset is 4.
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//
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// !0 = !{!"Simple C/C++ TBAA"}
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// !1 = !{!"omnipotent char", !0} // Scalar type node
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// !2 = !{!"short", !1} // Scalar type node
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// !3 = !{!"A", !2, i64 0} // Struct type node
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// !4 = !{!"B", !2, i64 0, !3, i64 4}
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// // Struct type node
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// !5 = !{!4, !2, i64 4} // Path tag node
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//
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// The struct type nodes and the scalar type nodes form a type DAG.
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// Root (!0)
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// char (!1) -- edge to Root
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// short (!2) -- edge to char
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// A (!3) -- edge with offset 0 to short
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// B (!4) -- edge with offset 0 to short and edge with offset 4 to A
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//
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// To check if two tags (tagX and tagY) can alias, we start from the base type
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// of tagX, follow the edge with the correct offset in the type DAG and adjust
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// the offset until we reach the base type of tagY or until we reach the Root
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// node.
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// If we reach the base type of tagY, compare the adjusted offset with
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// offset of tagY, return Alias if the offsets are the same, return NoAlias
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// otherwise.
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// If we reach the Root node, perform the above starting from base type of tagY
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// to see if we reach base type of tagX.
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//
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// If they have different roots, they're part of different potentially
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// unrelated type systems, so we return Alias to be conservative.
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// If neither node is an ancestor of the other and they have the same root,
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// then we say NoAlias.
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//
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// TODO: The current metadata format doesn't support struct
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// fields. For example:
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// struct X {
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// double d;
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// int i;
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// };
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// void foo(struct X *x, struct X *y, double *p) {
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// *x = *y;
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// *p = 0.0;
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// }
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// Struct X has a double member, so the store to *x can alias the store to *p.
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// Currently it's not possible to precisely describe all the things struct X
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// aliases, so struct assignments must use conservative TBAA nodes. There's
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// no scheme for attaching metadata to @llvm.memcpy yet either.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/TypeBasedAliasAnalysis.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/MemoryLocation.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/ErrorHandling.h"
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#include <cassert>
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#include <cstdint>
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using namespace llvm;
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// A handy option for disabling TBAA functionality. The same effect can also be
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// achieved by stripping the !tbaa tags from IR, but this option is sometimes
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// more convenient.
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static cl::opt<bool> EnableTBAA("enable-tbaa", cl::init(true), cl::Hidden);
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namespace {
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/// This is a simple wrapper around an MDNode which provides a higher-level
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/// interface by hiding the details of how alias analysis information is encoded
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/// in its operands.
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template<typename MDNodeTy>
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class TBAANodeImpl {
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MDNodeTy *Node = nullptr;
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public:
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TBAANodeImpl() = default;
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explicit TBAANodeImpl(MDNodeTy *N) : Node(N) {}
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/// getNode - Get the MDNode for this TBAANode.
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MDNodeTy *getNode() const { return Node; }
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/// getParent - Get this TBAANode's Alias tree parent.
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TBAANodeImpl<MDNodeTy> getParent() const {
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if (Node->getNumOperands() < 2)
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return TBAANodeImpl<MDNodeTy>();
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MDNodeTy *P = dyn_cast_or_null<MDNodeTy>(Node->getOperand(1));
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if (!P)
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return TBAANodeImpl<MDNodeTy>();
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// Ok, this node has a valid parent. Return it.
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return TBAANodeImpl<MDNodeTy>(P);
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}
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/// Test if this TBAANode represents a type for objects which are
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/// not modified (by any means) in the context where this
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/// AliasAnalysis is relevant.
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bool isTypeImmutable() const {
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if (Node->getNumOperands() < 3)
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return false;
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ConstantInt *CI = mdconst::dyn_extract<ConstantInt>(Node->getOperand(2));
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if (!CI)
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return false;
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return CI->getValue()[0];
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}
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};
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/// \name Specializations of \c TBAANodeImpl for const and non const qualified
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/// \c MDNode.
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/// @{
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using TBAANode = TBAANodeImpl<const MDNode>;
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using MutableTBAANode = TBAANodeImpl<MDNode>;
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/// @}
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/// This is a simple wrapper around an MDNode which provides a
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/// higher-level interface by hiding the details of how alias analysis
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/// information is encoded in its operands.
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template<typename MDNodeTy>
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class TBAAStructTagNodeImpl {
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/// This node should be created with createTBAAStructTagNode.
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MDNodeTy *Node;
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public:
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explicit TBAAStructTagNodeImpl(MDNodeTy *N) : Node(N) {}
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/// Get the MDNode for this TBAAStructTagNode.
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MDNodeTy *getNode() const { return Node; }
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MDNodeTy *getBaseType() const {
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return dyn_cast_or_null<MDNode>(Node->getOperand(0));
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}
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MDNodeTy *getAccessType() const {
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return dyn_cast_or_null<MDNode>(Node->getOperand(1));
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}
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uint64_t getOffset() const {
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return mdconst::extract<ConstantInt>(Node->getOperand(2))->getZExtValue();
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}
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/// Test if this TBAAStructTagNode represents a type for objects
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/// which are not modified (by any means) in the context where this
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/// AliasAnalysis is relevant.
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bool isTypeImmutable() const {
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if (Node->getNumOperands() < 4)
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return false;
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ConstantInt *CI = mdconst::dyn_extract<ConstantInt>(Node->getOperand(3));
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if (!CI)
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return false;
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return CI->getValue()[0];
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}
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};
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/// \name Specializations of \c TBAAStructTagNodeImpl for const and non const
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/// qualified \c MDNods.
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/// @{
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using TBAAStructTagNode = TBAAStructTagNodeImpl<const MDNode>;
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using MutableTBAAStructTagNode = TBAAStructTagNodeImpl<MDNode>;
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/// @}
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/// This is a simple wrapper around an MDNode which provides a
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/// higher-level interface by hiding the details of how alias analysis
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/// information is encoded in its operands.
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class TBAAStructTypeNode {
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/// This node should be created with createTBAAStructTypeNode.
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const MDNode *Node = nullptr;
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public:
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TBAAStructTypeNode() = default;
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explicit TBAAStructTypeNode(const MDNode *N) : Node(N) {}
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/// Get the MDNode for this TBAAStructTypeNode.
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const MDNode *getNode() const { return Node; }
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/// Get this TBAAStructTypeNode's field in the type DAG with
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/// given offset. Update the offset to be relative to the field type.
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TBAAStructTypeNode getParent(uint64_t &Offset) const {
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// Parent can be omitted for the root node.
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if (Node->getNumOperands() < 2)
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return TBAAStructTypeNode();
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// Fast path for a scalar type node and a struct type node with a single
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// field.
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if (Node->getNumOperands() <= 3) {
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uint64_t Cur = Node->getNumOperands() == 2
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? 0
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: mdconst::extract<ConstantInt>(Node->getOperand(2))
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->getZExtValue();
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Offset -= Cur;
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MDNode *P = dyn_cast_or_null<MDNode>(Node->getOperand(1));
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if (!P)
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return TBAAStructTypeNode();
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return TBAAStructTypeNode(P);
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}
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// Assume the offsets are in order. We return the previous field if
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// the current offset is bigger than the given offset.
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unsigned TheIdx = 0;
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for (unsigned Idx = 1; Idx < Node->getNumOperands(); Idx += 2) {
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uint64_t Cur = mdconst::extract<ConstantInt>(Node->getOperand(Idx + 1))
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->getZExtValue();
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if (Cur > Offset) {
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assert(Idx >= 3 &&
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"TBAAStructTypeNode::getParent should have an offset match!");
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TheIdx = Idx - 2;
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break;
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}
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}
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// Move along the last field.
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if (TheIdx == 0)
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TheIdx = Node->getNumOperands() - 2;
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uint64_t Cur = mdconst::extract<ConstantInt>(Node->getOperand(TheIdx + 1))
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->getZExtValue();
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Offset -= Cur;
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MDNode *P = dyn_cast_or_null<MDNode>(Node->getOperand(TheIdx));
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if (!P)
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return TBAAStructTypeNode();
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return TBAAStructTypeNode(P);
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}
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};
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} // end anonymous namespace
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/// Check the first operand of the tbaa tag node, if it is a MDNode, we treat
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/// it as struct-path aware TBAA format, otherwise, we treat it as scalar TBAA
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/// format.
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static bool isStructPathTBAA(const MDNode *MD) {
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// Anonymous TBAA root starts with a MDNode and dragonegg uses it as
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// a TBAA tag.
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return isa<MDNode>(MD->getOperand(0)) && MD->getNumOperands() >= 3;
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}
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AliasResult TypeBasedAAResult::alias(const MemoryLocation &LocA,
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const MemoryLocation &LocB) {
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if (!EnableTBAA)
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return AAResultBase::alias(LocA, LocB);
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// If accesses may alias, chain to the next AliasAnalysis.
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if (Aliases(LocA.AATags.TBAA, LocB.AATags.TBAA))
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return AAResultBase::alias(LocA, LocB);
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// Otherwise return a definitive result.
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return NoAlias;
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}
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bool TypeBasedAAResult::pointsToConstantMemory(const MemoryLocation &Loc,
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bool OrLocal) {
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if (!EnableTBAA)
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return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
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const MDNode *M = Loc.AATags.TBAA;
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if (!M)
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return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
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// If this is an "immutable" type, we can assume the pointer is pointing
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// to constant memory.
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if ((!isStructPathTBAA(M) && TBAANode(M).isTypeImmutable()) ||
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(isStructPathTBAA(M) && TBAAStructTagNode(M).isTypeImmutable()))
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return true;
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return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
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}
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FunctionModRefBehavior
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TypeBasedAAResult::getModRefBehavior(ImmutableCallSite CS) {
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if (!EnableTBAA)
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return AAResultBase::getModRefBehavior(CS);
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FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
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// If this is an "immutable" type, we can assume the call doesn't write
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// to memory.
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if (const MDNode *M = CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa))
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if ((!isStructPathTBAA(M) && TBAANode(M).isTypeImmutable()) ||
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(isStructPathTBAA(M) && TBAAStructTagNode(M).isTypeImmutable()))
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Min = FMRB_OnlyReadsMemory;
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return FunctionModRefBehavior(AAResultBase::getModRefBehavior(CS) & Min);
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}
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FunctionModRefBehavior TypeBasedAAResult::getModRefBehavior(const Function *F) {
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// Functions don't have metadata. Just chain to the next implementation.
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return AAResultBase::getModRefBehavior(F);
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}
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ModRefInfo TypeBasedAAResult::getModRefInfo(ImmutableCallSite CS,
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const MemoryLocation &Loc) {
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if (!EnableTBAA)
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return AAResultBase::getModRefInfo(CS, Loc);
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if (const MDNode *L = Loc.AATags.TBAA)
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if (const MDNode *M =
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CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa))
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if (!Aliases(L, M))
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return ModRefInfo::NoModRef;
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return AAResultBase::getModRefInfo(CS, Loc);
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}
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ModRefInfo TypeBasedAAResult::getModRefInfo(ImmutableCallSite CS1,
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ImmutableCallSite CS2) {
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if (!EnableTBAA)
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return AAResultBase::getModRefInfo(CS1, CS2);
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if (const MDNode *M1 =
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CS1.getInstruction()->getMetadata(LLVMContext::MD_tbaa))
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if (const MDNode *M2 =
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CS2.getInstruction()->getMetadata(LLVMContext::MD_tbaa))
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if (!Aliases(M1, M2))
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return ModRefInfo::NoModRef;
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return AAResultBase::getModRefInfo(CS1, CS2);
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}
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bool MDNode::isTBAAVtableAccess() const {
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if (!isStructPathTBAA(this)) {
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if (getNumOperands() < 1)
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return false;
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if (MDString *Tag1 = dyn_cast<MDString>(getOperand(0))) {
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if (Tag1->getString() == "vtable pointer")
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return true;
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}
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return false;
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}
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// For struct-path aware TBAA, we use the access type of the tag.
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if (getNumOperands() < 2)
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return false;
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MDNode *Tag = cast_or_null<MDNode>(getOperand(1));
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if (!Tag)
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return false;
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if (MDString *Tag1 = dyn_cast<MDString>(Tag->getOperand(0))) {
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if (Tag1->getString() == "vtable pointer")
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return true;
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}
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return false;
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}
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static bool matchAccessTags(const MDNode *A, const MDNode *B,
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const MDNode **GenericTag = nullptr);
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MDNode *MDNode::getMostGenericTBAA(MDNode *A, MDNode *B) {
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const MDNode *GenericTag;
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matchAccessTags(A, B, &GenericTag);
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return const_cast<MDNode*>(GenericTag);
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}
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static const MDNode *getLeastCommonType(const MDNode *A, const MDNode *B) {
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if (!A || !B)
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return nullptr;
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if (A == B)
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return A;
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SmallSetVector<const MDNode *, 4> PathA;
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TBAANode TA(A);
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while (TA.getNode()) {
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if (PathA.count(TA.getNode()))
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report_fatal_error("Cycle found in TBAA metadata.");
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PathA.insert(TA.getNode());
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TA = TA.getParent();
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}
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SmallSetVector<const MDNode *, 4> PathB;
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TBAANode TB(B);
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while (TB.getNode()) {
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if (PathB.count(TB.getNode()))
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report_fatal_error("Cycle found in TBAA metadata.");
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PathB.insert(TB.getNode());
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TB = TB.getParent();
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}
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int IA = PathA.size() - 1;
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int IB = PathB.size() - 1;
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const MDNode *Ret = nullptr;
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while (IA >= 0 && IB >= 0) {
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if (PathA[IA] == PathB[IB])
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Ret = PathA[IA];
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else
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break;
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--IA;
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--IB;
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}
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return Ret;
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}
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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);
|
|
}
|
|
|
|
static bool findAccessType(TBAAStructTagNode BaseTag,
|
|
const MDNode *AccessTypeNode,
|
|
uint64_t &OffsetInBase) {
|
|
// Start from the base type, follow the edge with the correct offset in
|
|
// the type DAG and adjust the offset until we reach the access type or
|
|
// until we reach a root node.
|
|
TBAAStructTypeNode BaseType(BaseTag.getBaseType());
|
|
OffsetInBase = BaseTag.getOffset();
|
|
|
|
while (const MDNode *BaseTypeNode = BaseType.getNode()) {
|
|
if (BaseTypeNode == AccessTypeNode)
|
|
return true;
|
|
|
|
// Follow the edge with the correct offset, Offset will be adjusted to
|
|
// be relative to the field type.
|
|
BaseType = BaseType.getParent(OffsetInBase);
|
|
}
|
|
return false;
|
|
}
|
|
|
|
static const MDNode *createAccessTag(const MDNode *AccessType) {
|
|
// If there is no access type or the access type is the root node, then
|
|
// we don't have any useful access tag to return.
|
|
if (!AccessType || AccessType->getNumOperands() < 2)
|
|
return nullptr;
|
|
|
|
Type *Int64 = IntegerType::get(AccessType->getContext(), 64);
|
|
auto *ImmutabilityFlag = ConstantAsMetadata::get(ConstantInt::get(Int64, 0));
|
|
Metadata *Ops[] = {const_cast<MDNode*>(AccessType),
|
|
const_cast<MDNode*>(AccessType), ImmutabilityFlag};
|
|
return MDNode::get(AccessType->getContext(), Ops);
|
|
}
|
|
|
|
/// matchTags - Return true if the given couple of accesses are allowed to
|
|
/// overlap. If \arg GenericTag is not null, then on return it points to the
|
|
/// most generic access descriptor for the given two.
|
|
static bool matchAccessTags(const MDNode *A, const MDNode *B,
|
|
const MDNode **GenericTag) {
|
|
if (A == B) {
|
|
if (GenericTag)
|
|
*GenericTag = A;
|
|
return true;
|
|
}
|
|
|
|
// Accesses with no TBAA information may alias with any other accesses.
|
|
if (!A || !B) {
|
|
if (GenericTag)
|
|
*GenericTag = nullptr;
|
|
return true;
|
|
}
|
|
|
|
// Verify that both input nodes are struct-path aware. Auto-upgrade should
|
|
// have taken care of this.
|
|
assert(isStructPathTBAA(A) && "Access A is not struct-path aware!");
|
|
assert(isStructPathTBAA(B) && "Access B is not struct-path aware!");
|
|
|
|
TBAAStructTagNode TagA(A), TagB(B);
|
|
const MDNode *CommonType = getLeastCommonType(TagA.getAccessType(),
|
|
TagB.getAccessType());
|
|
if (GenericTag)
|
|
*GenericTag = createAccessTag(CommonType);
|
|
|
|
// TODO: We need to check if AccessType of TagA encloses AccessType of
|
|
// TagB to support aggregate AccessType. If yes, return true.
|
|
|
|
// Climb the type DAG from base type of A to see if we reach base type of B.
|
|
uint64_t OffsetA;
|
|
if (findAccessType(TagA, TagB.getBaseType(), OffsetA))
|
|
return OffsetA == TagB.getOffset();
|
|
|
|
// Climb the type DAG from base type of B to see if we reach base type of A.
|
|
uint64_t OffsetB;
|
|
if (findAccessType(TagB, TagA.getBaseType(), OffsetB))
|
|
return OffsetB == TagA.getOffset();
|
|
|
|
// If the final access types have different roots, they're part of different
|
|
// potentially unrelated type systems, so we must be conservative.
|
|
if (!CommonType)
|
|
return true;
|
|
|
|
// If they have the same root, then we've proved there's no alias.
|
|
return false;
|
|
}
|
|
|
|
/// Aliases - Test whether the access represented by tag A may alias the
|
|
/// access represented by tag B.
|
|
bool TypeBasedAAResult::Aliases(const MDNode *A, const MDNode *B) const {
|
|
return matchAccessTags(A, B);
|
|
}
|
|
|
|
AnalysisKey TypeBasedAA::Key;
|
|
|
|
TypeBasedAAResult TypeBasedAA::run(Function &F, FunctionAnalysisManager &AM) {
|
|
return TypeBasedAAResult();
|
|
}
|
|
|
|
char TypeBasedAAWrapperPass::ID = 0;
|
|
INITIALIZE_PASS(TypeBasedAAWrapperPass, "tbaa", "Type-Based Alias Analysis",
|
|
false, true)
|
|
|
|
ImmutablePass *llvm::createTypeBasedAAWrapperPass() {
|
|
return new TypeBasedAAWrapperPass();
|
|
}
|
|
|
|
TypeBasedAAWrapperPass::TypeBasedAAWrapperPass() : ImmutablePass(ID) {
|
|
initializeTypeBasedAAWrapperPassPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
bool TypeBasedAAWrapperPass::doInitialization(Module &M) {
|
|
Result.reset(new TypeBasedAAResult());
|
|
return false;
|
|
}
|
|
|
|
bool TypeBasedAAWrapperPass::doFinalization(Module &M) {
|
|
Result.reset();
|
|
return false;
|
|
}
|
|
|
|
void TypeBasedAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.setPreservesAll();
|
|
}
|