[MrManatee]

Chris Lattner wrote a chapter about LLVM in The Architecture of Open Source Applications.

https://aosabook.org/en/llvm.html

Based on that, my understanding was that while intermediate representations were certainly not new, being strict about not mixing the layers was still quite rare. He specifically claims that GCC's GIMPLE is (was?) not a fully self-contained representation.

I'm not an expert in any of this. Just sharing the link.

[phicoh]

My experience with the Amsterdam Compile Kit (ACK) is that while ACK successfully managed to separate frontends, optimizers and backends using a single intermediate language, at the end it was the intermediate language that held it back.

The intermediate language was strongly stack oriented, to the extend that local CPU registers were mapped to stack locations. This worked well for pdp-11, vax, mc68k, and to some extent x86.

But when Sun's SPARC got popular it became clear that mapping stack register windows was not going to result in good performance.

One option would have been define a new register oriented intermediate language, just like llvm has now. But by that time research interests at the VU Amsterdam had shifted and this was never done.

[teddyh]

Interesting historical anecdote: ACK was briefly considered as a base for implementing GCC, but was rejected for licensing reasons.

[pjmlp]

Here is a paper about PL.8 research compiler used in IBM RISC research in mid-70's.

http://rsim.cs.illinois.edu/arch/qual_papers/compilers/ausla...

Key points, using a memory safe systems programming language which apparently would be too slow for the target hardware, thanks to the compiler IL representation and multiple execution phases (sounds similar?) achieves the goal of being usable to write OS in 70's hardware.