Go (Plan 9) syntax is not sufficiently different to make it a powerful intermediate representation, hence SSA as you point out. In fact many of the differences are frustrating subtle changes in instruction mnemonics or operand order. This might be okay if there was a canonical instruction database that made all these differences from Intel and AT&T easy to discover. However these exceptions are really recorded in various parts of the golang.org/x/arch/x86 repo. Producing the instruction database for avo was quite a time-consuming process. See:
https://github.com/mmcloughlin/avo/blob/master/internal/load... https://github.com/mmcloughlin/avo/issues/23
I've gained a lot more familiarity with the assembler and supporting infrastructure, so I'm hoping I may be able to contribute to this area of the core Go project.
https://github.com/mmcloughlin/avo/blob/0e253b3753beb409b3dd...
It gets to the point where the only source of truth is the Go assembler itself. My test suite takes the avo instruction database and generates a massive assembly file with one line per instruction form, then passes this to `go tool asm`.
It's quirks are annoying to start with, but if you use more than one assembly language you begin to see the advantages of a more consistent syntax between them.
I suspect the advantages for the go maintainers of a uniformish assembler syntax are the real reason for it.
LLVM MachineInstr and Cranelift do this much better than Go does, by maintaining a clean separation between the low-level IR and the assembly language.
I understand the rationale—that you can use the assembly syntax as a sort of IR by unifying the syntax of certain basic operations across different ISAs—but that's properly considered a low-level IR, not assembly. (It's also a pretty bad form of IR for doing any interesting optimizations, which is why Go uses a separate SSA form for that.)