[llvm] [RFC] Memory Model Relaxation Annotations (PR #78569)

[Nikita Popov via llvm-commits]

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+//===- MemoryModelRelaxationAnnotations.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
+/// This file provides utility for Memory Model Relaxation Annotations (MMRAs).
+/// Those annotations are represented using Metadata. The MMRATagSet class
+/// offers a simple API to parse the metadata and perform common operations on
+/// it. The MMRAMetadata class is a simple tuple of MDNode that provides easy
+/// access to all MMRA annotations on an instruction.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_IR_MEMORYMODELRELAXATIONANNOTATIONS_H
+#define LLVM_IR_MEMORYMODELRELAXATIONANNOTATIONS_H
+
+#include <set>
+#include <string>
+#include <tuple>
+#include <vector>
+
+namespace llvm {
+
+class MDNode;
+class MDTuple;
+class StringRef;
+class raw_ostream;
+class LLVMContext;
+class Instruction;
+
+/// Helper class for `!mmra` metadata nodes which can both build MMRA MDNodes,
+/// and parse them.
+///
+/// This can be visualized as a set of "tags", with each tag
+/// representing a particular property of an instruction, as
+/// explained in the MemoryModelRelaxationAnnotations docs.
+///
+/// This class (and the optimizer in general) does not reason
+/// about the exact nature of the tags and the properties they
+/// imply. It just sees the metadata as a collection of tags, which
+/// are a prefix/suffix pair of strings.
+class MMRAMetadata {
+public:
+  using TagT = std::pair<std::string, std::string>;
+  using SetT = std::set<TagT>;
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nikic wrote:

Is this an `std::set` for sorting purposes?

https://github.com/llvm/llvm-project/pull/78569