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Comment by Tehnix | Hacker News Reader

>A new compiler back end, based on static single-assignment form (SSA), has been under development for the past year

Huh, I was under the impression that either SSA or CPS was pretty standard for any serious compiler. Does anyone know why they didn't design it for this from the beginning? It's like one of the earlier things you learn when making actual compilers.

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It was more expedient to start with the Plan 9 tool chain that we had at the time. Ken was already familiar with the code base, which was small and compiled quickly (a few seconds). Because of this we got a lot done quickly, knowing that we would eventually modernize the compiler.

How much is Ken involved in the language today?

Ken is not really involved in the project these days. His last commit was in 2011, before Go 1 was even released.

(afaik) He retired around the Go 1.0 release, though he showed up as unixken on reddit during a Go Ask Me Anything.

https://www.reddit.com/r/golang/comments/46bd5h/ama_we_are_t...

> Huh, I was under the impression that either SSA or CPS was pretty standard for any serious compiler.

It was based on the Plan 9 compilers, which didn't use SSA.

SSA is standard for the middle end but not for the backend. According to my knowledge there are only two compilers with an SSA-based backend: libFirm (www.libfirm.org) and the Go compiler.

Obviously no backend is in SSA format after register allocation, but before allocation what do other compilers use if not SSA? Is there some kind of low-level LLVM and GCC IR separate from the front-end and middle one? That isn't in SSA?

I know that the C2 and Graal compilers are SSA all the way until register allocation is done.

You can stay in SSA form even after register allocation. In libFirm the assigned registers are just attributes of the values in the SSA representation. There was some additional discussion regarding this in [1].

GCC uses a separate representation (RTL) for their backend that is not in SSA form [2]. LLVM stays in SSA form for some backend phases but lowers the SSA form before register allocation (as also mentioned in [1]).

I took a quick look at the C2 and the Graal compiler. C2 seems to use LLVM's code generator (and thus lowers SSA before register allocation) but Graal seems to support SSA-based register allocation, nice.

[1] https://news.ycombinator.com/item?id=11210948

[2] https://en.wikibooks.org/wiki/GNU_C_Compiler_Internals/GNU_C...

I think you didn't understand Chris' post.

C2 is the HotSpot Server compiler. It definitely does not use LLVM anywhere.

Since there is also a programming language called C2, I took a look at the wrong compiler.

Can you provide a link to the source code?

https://github.com/dmlloyd/openjdk/tree/jdk9/jdk9/hotspot/sr...

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