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I'd be curious to see a "high-level structured assembly language" that gives the programmer actual control over things like register allocations, in a more syst

by kibwen 2y ago

I'd be curious to see a "high-level structured assembly language" that gives the programmer actual control over things like register allocations, in a more systematic way than C's attempt. You might say "optimizers will do a better job", and you're right, but what I want to see is a language that isn't designed to fed into an optimizing backend at all, but turned into machine code via simple, local transformations that a programmer can reliably predict. In other words, as high-level systems languages like C lean more and more heavily on optimizing backends and move away from being "portable assembly", I think that opens up a conceptual space somewhere below C yet still above assembly.

seanw444 2y ago
> You might say "optimizers will do a better job", and you're right That's probably why nothing good has been created to fill that space yet (that I know of). Any serious project is just going to opt for compiler optimizations.
- kibwen 2y ago
  The problem is that there are a handful of domains where optimizations need to be actively fought against, like low-level cryptography primitives. You can't write these in C reliably, so you need to drop into assembly to deliberately inhibit the optimizer, but that doesn't mean that assembly the ideal choice, only that it's the only choice.
mpreda 2y ago
I second this. It's nice to wish for the optimizer to do the [almost] perfect job, but sometimes that never arrives. Consider for example the case of AMD GPU ISA (GCN) generated by LLVM: it's been so far from optimal for so long, that one can lose hope that'll ever happen; and wish for a simple solution that works in the meantime.
- fweimer 2y ago
  Is the amdgcn GCC backend any better? (Or maybe final register allocation is not performed before llvm-mc is called—GCC reuses llvm-mc due to lack of binutils support.)
thuanao 2y ago
Sounds like Forth to me.
Someone 2y ago
I think you want a macro assembler. You may think that’s too close to the hardware, but if you want “actual control over things like register allocation”, you will be writing your code for a specific register set size, types of (vector) registers, etc, so you’ll soon be targeting a specific CPU. Also, was C ever “portable assembly”? There may have been a brief period where that was true, but it started as a language where programmers could fairly reliably predict what assembly the compiler would generated but that wasn’t portable, and once it had become portable, users wanted optimizations, so predicting what code it would generate was a lot harder.
pbsd 2y ago
Jasmin is something like this. It is essentially a high-level assembler, will handle register allocation (but not spills) for you, has some basic control flow primitives that map 1-to-1 to assembly instructions. There is also an optional formal verification component to prove some function is equivalent to its reference , is side-channel free, etc. [1] https://github.com/jasmin-lang/jasmin/wiki https://github.com/jasmin-lang/jasmin/wiki
- kibwen 2y ago
  Thanks, this looks quite interesting.

by kibwen 2y ago

seanw444 2y ago

> You might say "optimizers will do a better job", and you're right That's probably why nothing good has been created to fill that space yet (that I know of). Any serious project is just going to opt for compiler optimizations.

kibwen 2y ago
The problem is that there are a handful of domains where optimizations need to be actively fought against, like low-level cryptography primitives. You can't write these in C reliably, so you need to drop into assembly to deliberately inhibit the optimizer, but that doesn't mean that assembly the ideal choice, only that it's the only choice.

mpreda 2y ago

I second this. It's nice to wish for the optimizer to do the [almost] perfect job, but sometimes that never arrives. Consider for example the case of AMD GPU ISA (GCN) generated by LLVM: it's been so far from optimal for so long, that one can lose hope that'll ever happen; and wish for a simple solution that works in the meantime.

fweimer 2y ago
Is the amdgcn GCC backend any better? (Or maybe final register allocation is not performed before llvm-mc is called—GCC reuses llvm-mc due to lack of binutils support.)

thuanao 2y ago

Sounds like Forth to me.

Someone 2y ago

I think you want a macro assembler. You may think that’s too close to the hardware, but if you want “actual control over things like register allocation”, you will be writing your code for a specific register set size, types of (vector) registers, etc, so you’ll soon be targeting a specific CPU. Also, was C ever “portable assembly”? There may have been a brief period where that was true, but it started as a language where programmers could fairly reliably predict what assembly the compiler would generated but that wasn’t portable, and once it had become portable, users wanted optimizations, so predicting what code it would generate was a lot harder.

pbsd 2y ago

Jasmin is something like this. It is essentially a high-level assembler, will handle register allocation (but not spills) for you, has some basic control flow primitives that map 1-to-1 to assembly instructions. There is also an optional formal verification component to prove some function is equivalent to its reference , is side-channel free, etc. [1] https://github.com/jasmin-lang/jasmin/wiki https://github.com/jasmin-lang/jasmin/wiki

kibwen 2y ago
Thanks, this looks quite interesting.