llvm/llvm/include/llvm/IR/Analysis.h

//===- Analysis.h --------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
/// Pass manager infrastructure for declaring and invalidating analyses.
//===----------------------------------------------------------------------===//

#ifndef LLVM_IR_ANALYSIS_H
#define LLVM_IR_ANALYSIS_H

#include "llvm/ADT/SmallPtrSet.h"

namespace llvm {

class Function;
class Module;

/// A special type used by analysis passes to provide an address that
/// identifies that particular analysis pass type.
///
/// Analysis passes should have a static data member of this type and derive
/// from the \c AnalysisInfoMixin to get a static ID method used to identify
/// the analysis in the pass management infrastructure.
struct alignas(8) AnalysisKey { … };

/// A special type used to provide an address that identifies a set of related
/// analyses.  These sets are primarily used below to mark sets of analyses as
/// preserved.
///
/// For example, a transformation can indicate that it preserves the CFG of a
/// function by preserving the appropriate AnalysisSetKey.  An analysis that
/// depends only on the CFG can then check if that AnalysisSetKey is preserved;
/// if it is, the analysis knows that it itself is preserved.
struct alignas(8) AnalysisSetKey { … };

/// This templated class represents "all analyses that operate over \<a
/// particular IR unit\>" (e.g. a Function or a Module) in instances of
/// PreservedAnalysis.
///
/// This lets a transformation say e.g. "I preserved all function analyses".
///
/// Note that you must provide an explicit instantiation declaration and
/// definition for this template in order to get the correct behavior on
/// Windows. Otherwise, the address of SetKey will not be stable.
template <typename IRUnitT> class AllAnalysesOn { … };

template <typename IRUnitT> AnalysisSetKey AllAnalysesOn<IRUnitT>::SetKey;

extern template class AllAnalysesOn<Module>;
extern template class AllAnalysesOn<Function>;

/// Represents analyses that only rely on functions' control flow.
///
/// This can be used with \c PreservedAnalyses to mark the CFG as preserved and
/// to query whether it has been preserved.
///
/// The CFG of a function is defined as the set of basic blocks and the edges
/// between them. Changing the set of basic blocks in a function is enough to
/// mutate the CFG. Mutating the condition of a branch or argument of an
/// invoked function does not mutate the CFG, but changing the successor labels
/// of those instructions does.
class CFGAnalyses { … };

/// A set of analyses that are preserved following a run of a transformation
/// pass.
///
/// Transformation passes build and return these objects to communicate which
/// analyses are still valid after the transformation. For most passes this is
/// fairly simple: if they don't change anything all analyses are preserved,
/// otherwise only a short list of analyses that have been explicitly updated
/// are preserved.
///
/// This class also lets transformation passes mark abstract *sets* of analyses
/// as preserved. A transformation that (say) does not alter the CFG can
/// indicate such by marking a particular AnalysisSetKey as preserved, and
/// then analyses can query whether that AnalysisSetKey is preserved.
///
/// Finally, this class can represent an "abandoned" analysis, which is
/// not preserved even if it would be covered by some abstract set of analyses.
///
/// Given a `PreservedAnalyses` object, an analysis will typically want to
/// figure out whether it is preserved. In the example below, MyAnalysisType is
/// preserved if it's not abandoned, and (a) it's explicitly marked as
/// preserved, (b), the set AllAnalysesOn<MyIRUnit> is preserved, or (c) both
/// AnalysisSetA and AnalysisSetB are preserved.
///
/// ```
///   auto PAC = PA.getChecker<MyAnalysisType>();
///   if (PAC.preserved() || PAC.preservedSet<AllAnalysesOn<MyIRUnit>>() ||
///       (PAC.preservedSet<AnalysisSetA>() &&
///        PAC.preservedSet<AnalysisSetB>())) {
///     // The analysis has been successfully preserved ...
///   }
/// ```
class PreservedAnalyses { … };
} // namespace llvm

#endif