[PATCH] D138698: [clang-repl] Add basic documentation about clang-repl

[Sara Bellei via Phabricator via cfe-commits]

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https://reviews.llvm.org/D138698

Files:
  clang/docs/ClangRepl.rst
  clang/docs/ClangRepl_design.rst
  clang/docs/index.rst


Index: clang/docs/index.rst
===================================================================
--- clang/docs/index.rst
+++ clang/docs/index.rst
@@ -91,6 +91,7 @@
    ClangOffloadBundler
    ClangOffloadWrapper
    ClangOffloadPackager
+   ClangRepl
 
 Design Documents
 ================
Index: clang/docs/ClangRepl.rst
===================================================================
--- /dev/null
+++ clang/docs/ClangRepl.rst
@@ -0,0 +1,84 @@
+===========
+Clang-REPL
+===========
+
+**Clang-Repl** is an interactive C++ interpreter that allows for incremental
+compilation. It supports interactive programming for C++ in a REPL style,
+compiling the code just-in-time with a JIT approach that reduces the compile-run
+ cycles.
+
+Clang-Repl is suitable for any application where dynamic run-time modifiability
+and good numerical performance are required.
+
+Clang-Repl is a project derived from
+`Cling <https://github.com/root-project/cling>`_, a LLVM-based C/C++
+interpreter part of the the open-source data analysis framework
+`ROOT <https://root.cern/>`_, an open-source data analysis framework used by
+ high energy physics and others. Clang-Repl represents the effort to eliminate
+Cling’s dependence on ROOT, moving instead closer to the LLVM orbit.
+
+
+
+Why Clang-REPL?
+===============
+
+Several advantages arise from being hosted under the LLVM umbrella.
+As part of the larger LLVM project, Clang-Repl comes as part of the LLVM
+release cycles. Therefore, Clang-Repl follows the strict LLVM coding convention,
+and meets Clang’s quality standards, including diagnostic and complete AST
+representations. This has two consequences: 1. it helps in validating the
+quality, functionality, and vitality of Clang-Repl’s development on one side,
+and 2. It facilitates users who approach Clang-Repl, because they will learn
+how Clang-REPL works through the behavior of the compiler. Furthermore, some of
+Cling’s features are tailored specifically to work on
+`ROOT <https://root.cern/>`_, a software developed at
+`CERN <https://home.cern/>`_ to support the storage, analysis, and
+visualization of data from High-Energy Physics’s experiments. Clang-Repl can
+neglect those features that would not be useful outside the ROOT’s framework,
+and leverage the LLVM reduced API surface compared to ROOT’s one.
+
+
+How does Clang-REPL modify the compiling cycle
+==============================================
+
+.. image:: Clang-Repl_design.png
+   :align: center
+   :alt: Clang REPL design
+
+Clang-Repl compiler pipeline is represented by 8 phases:
+
+1. Clang-Repl controls the input infrastructure by interactive prompt or by an
+interface allowing the incremental processing of input.
+
+2. Then it sends the input to the underlying incremental facilities in Clang
+infrastructure (for simplicity libIncremental).
+
+3. Clang compiles the input into an AST representation.
+
+4. When required the AST can be further transformed in order to attach specific
+behavior.
+
+5. The AST representation is then lowered to LLVM IR.
+
+6. The LLVM IR is the input format for LLVM’s just-in-time (JIT) compilation
+infrastructure. The tool will instruct the JIT to run specified functions,
+translating them into machine code targeting the underlying device
+architecture (eg. Intel x86 or NVPTX).
+
+7. and 8. Clang-Repl can be integrated in existing applications or softwares.
+The concept of **Compiler as A Service** (**CaaS**) is now enabled: Clang-Repl
+changes the strategy to build tools in C++, supporting  interactive programming
+in a REPL style, compiling and binding code just-in-time. Offering support for
+a dynamic programming experience in C++ and control of the compiler
+simultaneously, Clang-Repl represents a tight integration between a high level
+dynamic C++ and a low level compiler.
+
+
+
+Related Reading
+===============
+`Cling Transitions to LLVM's Clang-Repl <https://root.cern/blog/cling-in-llvm/>`_
+
+`Moving (parts of) the Cling REPL in Clang <https://lists.llvm.org/pipermail/llvm-dev/2020-July/143257.html>`_
+
+`GPU Accelerated Automatic Differentiation With Clad <https://arxiv.org/pdf/2203.06139.pdf>`_

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