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269 lines
10 KiB
C++
269 lines
10 KiB
C++
//=====- CFLSummary.h - Abstract stratified sets implementation. --------=====//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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/// \file
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/// This file defines various utility types and functions useful to
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/// summary-based alias analysis.
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///
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/// Summary-based analysis, also known as bottom-up analysis, is a style of
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/// interprocedrual static analysis that tries to analyze the callees before the
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/// callers get analyzed. The key idea of summary-based analysis is to first
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/// process each function independently, outline its behavior in a condensed
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/// summary, and then instantiate the summary at the callsite when the said
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/// function is called elsewhere. This is often in contrast to another style
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/// called top-down analysis, in which callers are always analyzed first before
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/// the callees.
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///
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/// In a summary-based analysis, functions must be examined independently and
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/// out-of-context. We have no information on the state of the memory, the
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/// arguments, the global values, and anything else external to the function. To
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/// carry out the analysis conservative assumptions have to be made about those
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/// external states. In exchange for the potential loss of precision, the
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/// summary we obtain this way is highly reusable, which makes the analysis
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/// easier to scale to large programs even if carried out context-sensitively.
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///
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/// Currently, all CFL-based alias analyses adopt the summary-based approach
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/// and therefore heavily rely on this header.
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_ALIASANALYSISSUMMARY_H
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#define LLVM_ANALYSIS_ALIASANALYSISSUMMARY_H
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#include "llvm/ADT/DenseMapInfo.h"
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#include "llvm/ADT/Optional.h"
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#include "llvm/ADT/SmallVector.h"
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#include <bitset>
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namespace llvm {
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class CallBase;
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class Value;
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namespace cflaa {
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//===----------------------------------------------------------------------===//
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// AliasAttr related stuffs
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//===----------------------------------------------------------------------===//
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/// The number of attributes that AliasAttr should contain. Attributes are
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/// described below, and 32 was an arbitrary choice because it fits nicely in 32
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/// bits (because we use a bitset for AliasAttr).
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static const unsigned NumAliasAttrs = 32;
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/// These are attributes that an alias analysis can use to mark certain special
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/// properties of a given pointer. Refer to the related functions below to see
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/// what kinds of attributes are currently defined.
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typedef std::bitset<NumAliasAttrs> AliasAttrs;
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/// Attr represent whether the said pointer comes from an unknown source
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/// (such as opaque memory or an integer cast).
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AliasAttrs getAttrNone();
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/// AttrUnknown represent whether the said pointer comes from a source not known
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/// to alias analyses (such as opaque memory or an integer cast).
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AliasAttrs getAttrUnknown();
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bool hasUnknownAttr(AliasAttrs);
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/// AttrCaller represent whether the said pointer comes from a source not known
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/// to the current function but known to the caller. Values pointed to by the
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/// arguments of the current function have this attribute set
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AliasAttrs getAttrCaller();
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bool hasCallerAttr(AliasAttrs);
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bool hasUnknownOrCallerAttr(AliasAttrs);
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/// AttrEscaped represent whether the said pointer comes from a known source but
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/// escapes to the unknown world (e.g. casted to an integer, or passed as an
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/// argument to opaque function). Unlike non-escaped pointers, escaped ones may
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/// alias pointers coming from unknown sources.
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AliasAttrs getAttrEscaped();
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bool hasEscapedAttr(AliasAttrs);
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/// AttrGlobal represent whether the said pointer is a global value.
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/// AttrArg represent whether the said pointer is an argument, and if so, what
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/// index the argument has.
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AliasAttrs getGlobalOrArgAttrFromValue(const Value &);
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bool isGlobalOrArgAttr(AliasAttrs);
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/// Given an AliasAttrs, return a new AliasAttrs that only contains attributes
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/// meaningful to the caller. This function is primarily used for
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/// interprocedural analysis
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/// Currently, externally visible AliasAttrs include AttrUnknown, AttrGlobal,
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/// and AttrEscaped
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AliasAttrs getExternallyVisibleAttrs(AliasAttrs);
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//===----------------------------------------------------------------------===//
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// Function summary related stuffs
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//===----------------------------------------------------------------------===//
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/// The maximum number of arguments we can put into a summary.
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static const unsigned MaxSupportedArgsInSummary = 50;
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/// We use InterfaceValue to describe parameters/return value, as well as
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/// potential memory locations that are pointed to by parameters/return value,
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/// of a function.
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/// Index is an integer which represents a single parameter or a return value.
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/// When the index is 0, it refers to the return value. Non-zero index i refers
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/// to the i-th parameter.
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/// DerefLevel indicates the number of dereferences one must perform on the
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/// parameter/return value to get this InterfaceValue.
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struct InterfaceValue {
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unsigned Index;
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unsigned DerefLevel;
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};
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inline bool operator==(InterfaceValue LHS, InterfaceValue RHS) {
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return LHS.Index == RHS.Index && LHS.DerefLevel == RHS.DerefLevel;
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}
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inline bool operator!=(InterfaceValue LHS, InterfaceValue RHS) {
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return !(LHS == RHS);
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}
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inline bool operator<(InterfaceValue LHS, InterfaceValue RHS) {
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return LHS.Index < RHS.Index ||
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(LHS.Index == RHS.Index && LHS.DerefLevel < RHS.DerefLevel);
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}
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inline bool operator>(InterfaceValue LHS, InterfaceValue RHS) {
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return RHS < LHS;
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}
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inline bool operator<=(InterfaceValue LHS, InterfaceValue RHS) {
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return !(RHS < LHS);
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}
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inline bool operator>=(InterfaceValue LHS, InterfaceValue RHS) {
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return !(LHS < RHS);
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}
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// We use UnknownOffset to represent pointer offsets that cannot be determined
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// at compile time. Note that MemoryLocation::UnknownSize cannot be used here
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// because we require a signed value.
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static const int64_t UnknownOffset = INT64_MAX;
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inline int64_t addOffset(int64_t LHS, int64_t RHS) {
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if (LHS == UnknownOffset || RHS == UnknownOffset)
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return UnknownOffset;
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// FIXME: Do we need to guard against integer overflow here?
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return LHS + RHS;
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}
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/// We use ExternalRelation to describe an externally visible aliasing relations
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/// between parameters/return value of a function.
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struct ExternalRelation {
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InterfaceValue From, To;
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int64_t Offset;
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};
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inline bool operator==(ExternalRelation LHS, ExternalRelation RHS) {
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return LHS.From == RHS.From && LHS.To == RHS.To && LHS.Offset == RHS.Offset;
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}
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inline bool operator!=(ExternalRelation LHS, ExternalRelation RHS) {
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return !(LHS == RHS);
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}
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inline bool operator<(ExternalRelation LHS, ExternalRelation RHS) {
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if (LHS.From < RHS.From)
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return true;
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if (LHS.From > RHS.From)
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return false;
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if (LHS.To < RHS.To)
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return true;
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if (LHS.To > RHS.To)
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return false;
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return LHS.Offset < RHS.Offset;
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}
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inline bool operator>(ExternalRelation LHS, ExternalRelation RHS) {
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return RHS < LHS;
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}
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inline bool operator<=(ExternalRelation LHS, ExternalRelation RHS) {
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return !(RHS < LHS);
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}
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inline bool operator>=(ExternalRelation LHS, ExternalRelation RHS) {
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return !(LHS < RHS);
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}
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/// We use ExternalAttribute to describe an externally visible AliasAttrs
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/// for parameters/return value.
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struct ExternalAttribute {
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InterfaceValue IValue;
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AliasAttrs Attr;
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};
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/// AliasSummary is just a collection of ExternalRelation and ExternalAttribute
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struct AliasSummary {
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// RetParamRelations is a collection of ExternalRelations.
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SmallVector<ExternalRelation, 8> RetParamRelations;
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// RetParamAttributes is a collection of ExternalAttributes.
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SmallVector<ExternalAttribute, 8> RetParamAttributes;
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};
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/// This is the result of instantiating InterfaceValue at a particular call
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struct InstantiatedValue {
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Value *Val;
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unsigned DerefLevel;
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};
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Optional<InstantiatedValue> instantiateInterfaceValue(InterfaceValue IValue,
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CallBase &Call);
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inline bool operator==(InstantiatedValue LHS, InstantiatedValue RHS) {
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return LHS.Val == RHS.Val && LHS.DerefLevel == RHS.DerefLevel;
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}
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inline bool operator!=(InstantiatedValue LHS, InstantiatedValue RHS) {
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return !(LHS == RHS);
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}
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inline bool operator<(InstantiatedValue LHS, InstantiatedValue RHS) {
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return std::less<Value *>()(LHS.Val, RHS.Val) ||
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(LHS.Val == RHS.Val && LHS.DerefLevel < RHS.DerefLevel);
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}
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inline bool operator>(InstantiatedValue LHS, InstantiatedValue RHS) {
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return RHS < LHS;
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}
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inline bool operator<=(InstantiatedValue LHS, InstantiatedValue RHS) {
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return !(RHS < LHS);
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}
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inline bool operator>=(InstantiatedValue LHS, InstantiatedValue RHS) {
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return !(LHS < RHS);
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}
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/// This is the result of instantiating ExternalRelation at a particular
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/// callsite
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struct InstantiatedRelation {
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InstantiatedValue From, To;
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int64_t Offset;
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};
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Optional<InstantiatedRelation>
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instantiateExternalRelation(ExternalRelation ERelation, CallBase &Call);
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/// This is the result of instantiating ExternalAttribute at a particular
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/// callsite
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struct InstantiatedAttr {
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InstantiatedValue IValue;
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AliasAttrs Attr;
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};
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Optional<InstantiatedAttr> instantiateExternalAttribute(ExternalAttribute EAttr,
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CallBase &Call);
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}
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template <> struct DenseMapInfo<cflaa::InstantiatedValue> {
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static inline cflaa::InstantiatedValue getEmptyKey() {
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return cflaa::InstantiatedValue{DenseMapInfo<Value *>::getEmptyKey(),
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DenseMapInfo<unsigned>::getEmptyKey()};
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}
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static inline cflaa::InstantiatedValue getTombstoneKey() {
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return cflaa::InstantiatedValue{DenseMapInfo<Value *>::getTombstoneKey(),
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DenseMapInfo<unsigned>::getTombstoneKey()};
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}
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static unsigned getHashValue(const cflaa::InstantiatedValue &IV) {
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return DenseMapInfo<std::pair<Value *, unsigned>>::getHashValue(
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std::make_pair(IV.Val, IV.DerefLevel));
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}
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static bool isEqual(const cflaa::InstantiatedValue &LHS,
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const cflaa::InstantiatedValue &RHS) {
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return LHS.Val == RHS.Val && LHS.DerefLevel == RHS.DerefLevel;
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}
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};
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}
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#endif
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