Relicense fully to Apache-2.0 WITH LLVM-exception.

Large parts of the code in regalloc2 are currently licensed under the
Mozilla Public License (MPL) 2.0, because they derive in meaningful
ways from the register allocator in IonMonkey, which is part of
Firefox. The relevant source files are marked as such, with references
to the files in the Firefox source tree.

The intent of the regalloc2 project was to port the register allocator
from Firefox to use in Cranelift, borrowing good technology and
improving on it in the spirit of open source.

However, Several use-cases of Cranelift require, or at least strongly
prefer, the Apache-2.0 license with the LLVM exception (matching the
license of Cranelift itself, and Bytecode Alliance projects
generally). While using this license is not strictly necessary for
regalloc2 to be usable (The MPL is an excellent open-source license!),
relicensing fully under this license to harmonize with the rest of
Cranelift and Bytecode Alliance codebases significantly widens
possibilities and reduces friction; then regalloc2 is "just another
part of Cranelift" and doesn't have to be treated specially.

The source in `src/ion/` specifically began as a fairly direct port of
the algorithms in the following files in the `mozilla-central`
repository (Firefox codebase):

* The bulk of the "backtracking allocator" algorithm:
  * `js/src/jit/BacktrackingAllocator.{cpp,h}`
* Helpers and definitions in the surrounding infrastructure:
  * `js/src/jit/RegisterAllocator.h`
  * `js/src/jit/RegisterAllocator.cpp`
  * `js/src/jit/StackSlotAllocator.h`
  * `js/src/jit/LIR.h`
* A few data structure implementations:
  * `js/src/ds/SplayTree.h`
  * `js/src/ds/PriorityQueue.h`

Subsequent work in improving regalloc2 has caused it to drift from the
direct port -- for example, it no longer uses splay trees or the
direct port of the priority queue above -- but it is of course very
clearly still a derivative work.

Analysis of the contributors to these files indicates that we need
signoff from the following folks:

* Mozilla Corp, for contributions made by Mozilla employees (the
  majority of the code). Communications with Mozilla (thanks
  @tschneidereit and @bholley for doing the work here!) indicate that
  @ekr is able to sign off when ready here.

* Andy Wingo, specifically for the work done in [Bug
  1620197](https://bugzilla.mozilla.org/show_bug.cgi?id=1620197) and
  [Bug 1609057](https://bugzilla.mozilla.org/show_bug.cgi?id=1609057) to
  generalize the stack allocator for a Wasm feature (multiple returns).

Additionally, since the initial port, we have had three contributions
from @Amanieu:
[#9](#9),
[#11](#11),
[#13](#13).

So, if everyone applicable is happy with this relicensing, this PR
removes the MPL-2.0 license in `src/ion/` and marks all files as
covered under `Apache-2.0 WITH LLVM-exception`. Please let us know if
this is OK!

Signoffs:

- [ ] @ekr, for Mozilla's contributions
- [ ] @wingo, for contributions to original code in `mozilla-central`
- [ ] @Amanieu, for the three PRs linked above

Thanks!

Cargo.toml

@@ -3,7 +3,7 @@ name = "regalloc2"
 version = "0.0.1"
 authors = ["Chris Fallin <chris@cfallin.org>", "Mozilla SpiderMonkey Developers"]
 edition = "2018"
-license = "Apache-2.0 WITH LLVM-exception AND MPL-2.0"
+license = "Apache-2.0 WITH LLVM-exception"
 description = "Backtracking register allocator inspired from IonMonkey"
 repository = "https://github.com/bytecodealliance/regalloc2"
 

README.md

@@ -15,18 +15,8 @@ how the allocator works.
 
 ## License
 
-Unless otherwise specified, code in this crate is licensed under the Apache 2.0
-License with LLVM Exception. This license text can be found in the file
-`LICENSE`.
-
-Files in the `src/ion/` directory are directly ported from original C++ code in
-IonMonkey, a part of the Firefox codebase. Parts of `src/lib.rs` are also
-definitions that are directly translated from this original code. As a result,
-these files are derivative works and are covered by the Mozilla Public License
-(MPL) 2.0, as described in license headers in those files. Please see the
-notices in relevant files for links to the original IonMonkey source files from
-which they have been translated/derived. The MPL text can be found in
-`src/ion/LICENSE`.
+This crate is licensed under the Apache 2.0 License with LLVM
+Exception. This license text can be found in the file `LICENSE`.
 
 Parts of the code are derived from regalloc.rs: in particular,
 `src/checker.rs` and `src/domtree.rs`. This crate has the same license

src/ion/data_structures.rs

@@ -1,11 +1,10 @@
 /*
- * The following license applies to this file, which was initially
- * derived from the files `js/src/jit/BacktrackingAllocator.h` and
- * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox:
- *
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ * This file was initially derived from the files
+ * `js/src/jit/BacktrackingAllocator.h` and
+ * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox, and was
+ * originally licensed under the Mozilla Public License 2.0. We
+ * subsequently relicensed it to Apache-2.0 WITH LLVM-exception (see
+ * https://github.com/bytecodealliance/regalloc2/issues/7).
  *
  * Since the initial port, the design has been substantially evolved
  * and optimized.

src/ion/liveranges.rs

@@ -1,11 +1,10 @@
 /*
- * The following license applies to this file, which was initially
- * derived from the files `js/src/jit/BacktrackingAllocator.h` and
- * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox:
- *
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ * This file was initially derived from the files
+ * `js/src/jit/BacktrackingAllocator.h` and
+ * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox, and was
+ * originally licensed under the Mozilla Public License 2.0. We
+ * subsequently relicensed it to Apache-2.0 WITH LLVM-exception (see
+ * https://github.com/bytecodealliance/regalloc2/issues/7).
  *
  * Since the initial port, the design has been substantially evolved
  * and optimized.

src/ion/merge.rs

@@ -1,11 +1,10 @@
 /*
- * The following license applies to this file, which was initially
- * derived from the files `js/src/jit/BacktrackingAllocator.h` and
- * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox:
- *
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ * This file was initially derived from the files
+ * `js/src/jit/BacktrackingAllocator.h` and
+ * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox, and was
+ * originally licensed under the Mozilla Public License 2.0. We
+ * subsequently relicensed it to Apache-2.0 WITH LLVM-exception (see
+ * https://github.com/bytecodealliance/regalloc2/issues/7).
  *
  * Since the initial port, the design has been substantially evolved
  * and optimized.

src/ion/mod.rs

@@ -1,11 +1,10 @@
 /*
- * The following license applies to this file, which was initially
- * derived from the files `js/src/jit/BacktrackingAllocator.h` and
- * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox:
- *
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ * This file was initially derived from the files
+ * `js/src/jit/BacktrackingAllocator.h` and
+ * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox, and was
+ * originally licensed under the Mozilla Public License 2.0. We
+ * subsequently relicensed it to Apache-2.0 WITH LLVM-exception (see
+ * https://github.com/bytecodealliance/regalloc2/issues/7).
  *
  * Since the initial port, the design has been substantially evolved
  * and optimized.

src/ion/moves.rs

@@ -1,11 +1,10 @@
 /*
- * The following license applies to this file, which was initially
- * derived from the files `js/src/jit/BacktrackingAllocator.h` and
- * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox:
- *
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ * This file was initially derived from the files
+ * `js/src/jit/BacktrackingAllocator.h` and
+ * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox, and was
+ * originally licensed under the Mozilla Public License 2.0. We
+ * subsequently relicensed it to Apache-2.0 WITH LLVM-exception (see
+ * https://github.com/bytecodealliance/regalloc2/issues/7).
  *
  * Since the initial port, the design has been substantially evolved
  * and optimized.

src/ion/process.rs

@@ -1,11 +1,10 @@
 /*
- * The following license applies to this file, which was initially
- * derived from the files `js/src/jit/BacktrackingAllocator.h` and
- * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox:
- *
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ * This file was initially derived from the files
+ * `js/src/jit/BacktrackingAllocator.h` and
+ * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox, and was
+ * originally licensed under the Mozilla Public License 2.0. We
+ * subsequently relicensed it to Apache-2.0 WITH LLVM-exception (see
+ * https://github.com/bytecodealliance/regalloc2/issues/7).
  *
  * Since the initial port, the design has been substantially evolved
  * and optimized.

src/ion/requirement.rs

@@ -1,3 +1,15 @@
+/*
+ * This file was initially derived from the files
+ * `js/src/jit/BacktrackingAllocator.h` and
+ * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox, and was
+ * originally licensed under the Mozilla Public License 2.0. We
+ * subsequently relicensed it to Apache-2.0 WITH LLVM-exception (see
+ * https://github.com/bytecodealliance/regalloc2/issues/7).
+ *
+ * Since the initial port, the design has been substantially evolved
+ * and optimized.
+ */
+
 //! Requirements computation.
 
 use super::{Env, LiveBundleIndex};

src/ion/spill.rs

@@ -1,11 +1,10 @@
 /*
- * The following license applies to this file, which was initially
- * derived from the files `js/src/jit/BacktrackingAllocator.h` and
- * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox:
- *
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ * This file was initially derived from the files
+ * `js/src/jit/BacktrackingAllocator.h` and
+ * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox, and was
+ * originally licensed under the Mozilla Public License 2.0. We
+ * subsequently relicensed it to Apache-2.0 WITH LLVM-exception (see
+ * https://github.com/bytecodealliance/regalloc2/issues/7).
  *
  * Since the initial port, the design has been substantially evolved
  * and optimized.

src/ion/stackmap.rs

@@ -1,11 +1,10 @@
 /*
- * The following license applies to this file, which was initially
- * derived from the files `js/src/jit/BacktrackingAllocator.h` and
- * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox:
- *
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ * This file was initially derived from the files
+ * `js/src/jit/BacktrackingAllocator.h` and
+ * `js/src/jit/BacktrackingAllocator.cpp` in Mozilla Firefox, and was
+ * originally licensed under the Mozilla Public License 2.0. We
+ * subsequently relicensed it to Apache-2.0 WITH LLVM-exception (see
+ * https://github.com/bytecodealliance/regalloc2/issues/7).
  *
  * Since the initial port, the design has been substantially evolved
  * and optimized.