Show HN: A pure Go library for interacting with LLVM IR (opens in new tab)

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81 pointsmewmew8y ago9 comments

9 comments

LLVM IR is being changed at a high rate. While there are some weak backward-compatibility promises (older, but not too much old, bitcode can be read by newer official IR readers), new features are introduced overnight. I expect this project to be a high maintenance job to keep up with the LLVM trunk.

mewmewOP8y ago

@krasin The LLVM IR assembly language does change with a rather high rate. Not too often to be unfeasible, but an external project definitely needs to make sure it can keep up with maintenance to remain useful. Since the llir/llvm project started back in 2014, the LLVM IR assembly language has had one major change, and that is the new metadata syntax introduced in LLVM 3.6.

To facilitate maintenance efforts over time, a BNF grammar for LLVM IR assembly has been written, from which the lexer and parser are generated [1,2,3]. The intention is for this BNF grammar to eventually become the basis or starting ground for an official BNF grammar of the LLVM IR assembly language (but that's a different project altogether, and a huge effort in itself).

[1]: https://github.com/llir/llvm/blob/master/asm/internal/ll.bnf

[2]: https://github.com/llir/grammar

[3]: https://github.com/goccmack/gocc

krasin8y ago

@mewmew, have you already added support for .bc files which have multiple bitcode modules (aka merged modules)? These are used in the work-in-progress ThinLTO.

Merged modules were a major change to LLVM. And this part is still evolving. Like, the last breaking change was 16 days ago: https://github.com/llvm-mirror/llvm/commit/e74c64e05ab257c37...

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jpsim8y ago

Maybe this would lend itself well to parsing bitcode slices (serialized LLVM IR). I've often wanted to diff bitcode produced by different compiler versions.

boulos8y ago

What's wrong with llvm-diff [1]? Is it that you want to compare across bitcode versions that weren't backwards compatible? (so the current llvm-diff won't parse an old old bitcode)

[1] http://llvm.org/docs/CommandGuide/llvm-diff.html

jpsim8y ago

llvm-diff is indeed pretty great, but having the IR structure as an AST that you could programmatically access and manipulate would allow more semantic diffing, or integration into workflows that would benefit from structured representations of a diff.

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9 comments

krasin8y ago

mewmewOP8y ago

[1]: https://github.com/llir/llvm/blob/master/asm/internal/ll.bnf

[2]: https://github.com/llir/grammar

[3]: https://github.com/goccmack/gocc

krasin8y ago

@mewmew, have you already added support for .bc files which have multiple bitcode modules (aka merged modules)? These are used in the work-in-progress ThinLTO.

Merged modules were a major change to LLVM. And this part is still evolving. Like, the last breaking change was 16 days ago: https://github.com/llvm-mirror/llvm/commit/e74c64e05ab257c37...

1 more reply

jpsim8y ago

Maybe this would lend itself well to parsing bitcode slices (serialized LLVM IR). I've often wanted to diff bitcode produced by different compiler versions.

boulos8y ago

What's wrong with llvm-diff [1]? Is it that you want to compare across bitcode versions that weren't backwards compatible? (so the current llvm-diff won't parse an old old bitcode)

[1] http://llvm.org/docs/CommandGuide/llvm-diff.html

jpsim8y ago

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