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[clang-repl] Recommit "Land initial infrastructure for incremental parsing"

Authored by v.g.vassilev on May 12 2021, 10:41 PM.

Description

[clang-repl] Recommit "Land initial infrastructure for incremental parsing"

Original commit message:

In http://lists.llvm.org/pipermail/llvm-dev/2020-July/143257.html we have
mentioned our plans to make some of the incremental compilation facilities
available in llvm mainline.

This patch proposes a minimal version of a repl, clang-repl, which enables
interpreter-like interaction for C++. For instance:

./bin/clang-repl
clang-repl> int i = 42;
clang-repl> extern "C" int printf(const char*,...);
clang-repl> auto r1 = printf("i=%d\n", i);
i=42
clang-repl> quit

The patch allows very limited functionality, for example, it crashes on invalid
C++. The design of the proposed patch follows closely the design of cling. The
idea is to gather feedback and gradually evolve both clang-repl and cling to
what the community agrees upon.

The IncrementalParser class is responsible for driving the clang parser and
codegen and allows the compiler infrastructure to process more than one input.
Every input adds to the “ever-growing” translation unit. That model is enabled
by an IncrementalAction which prevents teardown when HandleTranslationUnit.

The IncrementalExecutor class hides some of the underlying implementation
details of the concrete JIT infrastructure. It exposes the minimal set of
functionality required by our incremental compiler/interpreter.

The Transaction class keeps track of the AST and the LLVM IR for each
incremental input. That tracking information will be later used to implement
error recovery.

The Interpreter class orchestrates the IncrementalParser and the
IncrementalExecutor to model interpreter-like behavior. It provides the public
API which can be used (in future) when using the interpreter library.

Differential revision: https://reviews.llvm.org/D96033

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