QUILC

Quilc is an advanced optimizing compiler for the quantum instruction language Quil, licensed under the Apache 2.0 license.

Quilc comprises two projects. The first, cl-quil, does the heavy lifting of parsing, compiling, and optimizing Quil code. The second, quilc, presents an external interface for using cl-quil, either using the binary quilc application directly, or alternatively by communicating with an RPCQ server.

Quil is the quantum instruction language developed at Rigetti Computing. In Quil quantum algorithms are expressed using Quil's standard gates and instructions. One can also use Quil's DEFGATE to define new non-standard gates, and DEFCIRCUIT to build a named circuit that can be referenced elsewhere in Quil code (analogous to a function in most other programming languages).

Quil Compiler

This directory contains the quilc application. quilc takes as input arbitrary Quil code, either provided directly to the binary or to the quilc server, and produces optimized Quil code. The compiled code is optimized for the configured instruction set architecture (ISA), targeting the native gates specified by the ISA.

Cloning the repository

To clone the quilc repository and its bundled submodules, run the following command:

git clone --recurse-submodules https://github.com/rigetti/quilc.git

Building the Quil Compiler

Prerequisites to building quilc are:

1. Standard UNIX build tools
2. SBCL (a recent version, but not SBCL 1.5.6): Common Lisp compiler
3. Quicklisp: Common Lisp library manager
4. ZeroMQ: Messaging library required by RPCQ. Development headers are required at build time.

Follow these instructions to get started from scratch.

One notorious dependency is MAGICL. It is available on Quicklisp, but requires you to install some system libraries such as BLAS, LAPACK, and libffi. Follow MAGICL's instructions carefully before proceeding with loading CL-QUIL or makeing quilc.

Once these dependencies are installed, building should be easy. Building the quilc binary is automated using the Makefile:

$ make quilc

This will create a binary quilc in the current directory

$ ./quilc --version

To install system-wide issue the command

$ make install

Build flags

quilc can be built with additional options provided to make as described below:

Flag	Description
POST_LOAD_ASDF_SYSTEMS	Specify additional ASDF systems to load after quilc as part of the executable. This can be used to build quilc with additional out-of-tree functionality.

Using the Quil Compiler

The Quil Compiler provides two modes of interaction: (1) communicating directly with the quilc binary, providing your Quil code over stdin; or (2) communicating with the quilc server.

quilc

The quilc binary reads Quil code provided on stdin:

$ echo H 0 | quilc
$ cat large_file.quil | quilc

Server

For various reasons (e.g. not having to repeatedly load the quilc binary into memory, communicating over a network) quilc provides a an RPCQ server interface. RPCQ is an open-source RPC framework developed at Rigetti for efficient network communication through the QCS stack. The server is started in RPCQ-mode using the -R flag

$ quilc -R
+-----------------+
|  W E L C O M E  |
|   T O   T H E   |
|  R I G E T T I  |
|     Q U I L     |
| C O M P I L E R |
+-----------------+
Copyright (c) 2016-2019 Rigetti Computing.

<134>1 2019-01-29T22:03:08Z workstation.local ./quilc 4077 LOG0001 - Launching quilc.
<134>1 2019-01-29T22:03:08Z workstation.local ./quilc 4077 - - Spawning server at (tcp://*:5555) .

The server-mode provides to high-level languages such as Python a way to communicate with the Quil compiler, thus enabling high-level abstractions and tools that are not directly available in Quil. The pyquil library provides such an interface to quilc.

CL-QUIL

CL-QUIL is the Lisp library that implements parsing and compiling of Quil code. The code can be found under ./src/. Other lisp libraries, including quilc, can depend on it.

Usage

To get up and running quickly using the quilc Docker image, head directly to the section "Running the Quil Compiler with Docker" below. Otherwise, the following steps will walk you through how to build the compiler from source.

Follow the instructions in QVM's doc/lisp-setup.md to satisfy the dependencies required to load the CL-QUIL library. Afterwhich, the library can be loaded

$ sbcl

* (ql:quickload :cl-quil)
;;; <snip>compilation output</snip>
(:CL-QUIL)
* (cl-quil:parse-quil "H 0")
#<CL-QUIL:PARSED-PROGRAM {100312C643}>

A few good entry points to exploring the library are:

• The functions cl-quil::parse-quil in src/parser.lisp, and cl-quil:parse-quil in src/cl-quil.lisp and the various transforms therein.
• The function cl-quil:compiler-hook which constructs a control-flow graph (CFG) and then performs various optimizations on the CFG.

Automated Build, Test, and Release with Docker

The CI pipeline for quilc produces a Docker image, available at rigetti/quilc. To get the latest stable version of quilc, run docker pull rigetti/quilc. To instead pull a specific version of quilc, run docker pull rigetti/quilc:VERSION, where VERSION is something like 1.10.4.

The Dockerfile for quilc builds from three parent Docker images:

1. rigetti/lisp: Contains SBCL, Quicklisp, and third-party libraries.
2. rigetti/rpcq: Contains the message spec and RPC framework used by quilc.
3. rigetti/qvm: Contains the Quantum Virtual Machine, used in the quilc tests.

The Dockerfile for quilc intentionally pins the versions of these three images, which means that the version numbers must be actively incremented as necessary. If the build for quilc is failing, this is probably the place to look, because the unit tests are run inside of a freshly-built quilc Docker image as part of the GitLab CI pipeline.

Running the Quil Compiler with Docker

As outlined above, the Quil Compiler supports two modes of operation: stdin and server.

To run quilc in stdin mode, do one either of the following:

1. The containerized compiler will then read whatever newline-separated Quil instructions you enter, waiting for an EOF signal (Control+d) to compile it.

docker run --rm -it rigetti/quilc

2. You can alternatively pipe Quil instructions into the quilc container if you drop the -t.

echo H 0 | docker run --rm -i rigetti/quilc

To run quilc in server mode, do the following:

docker run --rm -it -p 5555:5555 rigetti/quilc -R

This will spawn an RPCQ-mode quilc server, that you can communicate with over TCP. If you would like to change the port of the server to PORT, you can alter the command as follows:

docker run --rm -it -p PORT:PORT rigetti/quilc -R -p PORT

Ports 5555 and 6000 are exposed using the EXPOSE directive in the rigetti/quilc image, so you can additionally use the -P option to automatically bind these container ports to randomly assigned host ports. You can then inspect the mapping using docker port CONTAINER [PORT].

Release Process

1. Update VERSION.txt and push the commit to master.
2. Push a git tag vX.Y.Z that contains the same version number as in VERSION.txt.
3. Verify that the resulting build (triggered by pushing the tag) completes successfully.
4. Publish a release using the tag as the name.
5. Close the milestone associated with this release, and migrate incomplete issues to the next one.
6. Update the quilc version of downstream dependencies (if applicable, see next section).

Downstream Dependencies

Currently, there are a couple different components of the Forest SDK that depend on quilc:

1. qvm
2. pyquil
3. forest-benchmarking

It is the responsibility of the releaser to verify that the latest quilc release does not break the test suites of these downstream dependencies. All of these repositories pull the latest released version of quilc as part of their CI pipelines.

Benchmarking

quilc offers a benchmarking suite to compare its performance against other compilers and between its own versions. To run the benchmark suite, move to the quilc root directory, make sure the git submodules are checked out, and run

make benchmark-qasm

Get involved!

We welcome and encourage community contributions! Peruse our guidelines for contributing to get you up to speed on expectations. Once that's clear, a good place to start is the good first issue section. If you find any bugs, please create an issue. If you need help with some code or want to discuss some technical issues, you can find us in the #dev channel on Slack or in the #qlisp channel on freenode IRC.

We look forward to meeting and working with you!

Incompatible software versions

SBCL 1.5.6

There is an issue with SBCL 1.5.6 that results in unhandled memory faults in SB-VM::FUNCALLABLE-INSTANCE-TRAMP when attempting to run quilc compiled with that version of SBCL. The issue was resolved with SBCL commit 550c4d2. For this reason, it's not possible to use quilc or cl-quil with SBCL 1.5.6, but any other recent SBCL version should work fine.