llvm/lib/Target/WebAssembly
JF Bastien c37a088af2 [WebAssembly] Add Relooper
This is just an initial checkin of an implementation of the Relooper algorithm, in preparation for WebAssembly codegen to utilize. It doesn't do anything yet by itself.

The Relooper algorithm takes an arbitrary control flow graph and generates structured control flow from that, utilizing a helper variable when necessary to handle irreducibility. The WebAssembly backend will be able to use this in order to generate an AST for its binary format.

Author: azakai

Reviewers: jfb, sunfish

Subscribers: jevinskie, arsenm, jroelofs, llvm-commits

Differential revision: http://reviews.llvm.org/D11691

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245142 91177308-0d34-0410-b5e6-96231b3b80d8
2015-08-15 01:23:28 +00:00
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//===-- README.txt - Notes for WebAssembly code gen -----------------------===//

This WebAssembly backend is presently in a very early stage of development.
The code should build and not break anything else, but don't expect a lot more
at this point.

For more information on WebAssembly itself, see the design documents:
  * https://github.com/WebAssembly/design/blob/master/README.md

The following documents contain some information on the planned semantics and
binary encoding of WebAssembly itself:
  * https://github.com/WebAssembly/design/blob/master/AstSemantics.md
  * https://github.com/WebAssembly/design/blob/master/BinaryEncoding.md

Interesting work that remains to be done:
* Write a pass to restructurize irreducible control flow. This needs to be done
  before register allocation to be efficient, because it may duplicate basic
  blocks and WebAssembly performs register allocation at a whole-function
  level. Note that LLVM's GPU code has such a pass, but it linearizes control
  flow (e.g. both sides of branches execute and are masked) which is undesirable
  for WebAssembly.
* Basic relooper to expose control flow as an AST.
* Figure out how to properly use MC for virtual ISAs. This may require some
  refactoring of MC.

//===---------------------------------------------------------------------===//