Function declaration confusion · cranelift

Stream: cranelift

Topic: Function declaration confusion

osa1 (May 13 2020 at 23:32):

I have functions A and B, and B uses a pointer to A (but does not call it!). How do I need to declare A in B? I generate code for A before B in the same module, which looks like

function u0:34(i64, i64) -> i64 system_v {
    sig0 = (i64) -> i64 system_v
    fn0 = u0:0 sig0

block0(v0: i64, v2: i64):
    v1 = load.i64 v0+8
    v3 = iadd v1, v2
    return v3
}

Now when generating B I use Variable(34) (which is the previous function shown above), but it fails with variable Variable(34) is used but its type has not been declared.

bjorn3 (May 14 2020 at 09:13):

@osa1 You need to use module.declare_func_in_func(a_func_id, &mut b_func) to get a FuncRef to A.

osa1 (May 14 2020 at 09:50):

I'm confused, why do I need a FuncRef? I'm not calling it, I'm just returning it.

bjorn3 (May 14 2020 at 09:53):

In that case you can use the func_addr instruction to get the address of the function from the FuncRef.

osa1 (May 14 2020 at 09:59):

What is the iAddr argument for in func_addr?

bjorn3 (May 14 2020 at 10:07):

The pointer type. Eg i64 on 64bit systems and i32 on 32bit systems.

So if I understand this correctly, I need to get a FuncId for every function in this compilation unit first, and then maintain a map from my variable type to FuncIds, and check, on every use, whether the used variable is a function

osa1 (May 14 2020 at 10:08):

If it is then I need to first import it (declare_func_in_func) and then get address of it using func_addr

osa1 (May 14 2020 at 10:08):

In my language I don't do direct calls (maybe later after optimizations)

bjorn3 (May 14 2020 at 10:12):

Yes, you need to use declare_func_in_func followed by func_addr to get the address of a function.

osa1 (May 14 2020 at 10:13):

Thank you! Really helpful

osa1 (May 14 2020 at 10:20):

When building a module with multiple functions do I have to use https://docs.rs/cranelift-codegen/0.63.0/cranelift_codegen/struct.Context.html or can I create a FunctionBuilder for every function?

osa1 (May 14 2020 at 10:21):

So instead of FunctionBuilder::new(&mut context.func, ...); can I do let mut func = Function::with_name_signature(...); let mut builder = FunctionBuilder::new(&mut func, &mut fn_builder_ctx); ?

osa1 (May 14 2020 at 10:28):

Is the "entry basic block" stuff gone in the latest version? Saw that in an older code

bjorn3 (May 14 2020 at 10:34):

You can reuse Context for multiple functions if you call .clear() in between. This is not necessary, but improves performance. You can't reuse FunctionBuilder. Everything that is reusable for cranelift-frontend is stored in FunctionBuilderContext instead.

bjorn3 (May 14 2020 at 10:35):

What do you mean with "entry basic block" stuff?

osa1 (May 14 2020 at 10:36):

create_ebb and append_ebb_params_for_function_params, they seem to be gone now

osa1 (May 14 2020 at 10:36):

How do I create an entry basic block and declare function arguments there in the latest version on crates.io?

osa1 (May 14 2020 at 10:50):

If I want the function parameters to be available in all blocks of the function do I need to do `builder.append_block_params_for_function_params(block); for every block?

bjorn3 (May 14 2020 at 10:53):

create_ebb has been renamed to create_block.

bjorn3 (May 14 2020 at 10:53):

osa1 said:

If I want the function parameters to be available in all blocks of the function do I need to do `builder.append_block_params_for_function_params(block); for every block?

Only do it for the entry block. You can the access the params from all blocks.

osa1 (May 14 2020 at 10:54):

I don't understand how to do that. Since entry block creating is not different than others, how do I specify which block is the entry block?

bjorn3 (May 14 2020 at 10:54):

Just use builder.block_params(entry_block)[0] to get the first param.

bjorn3 (May 14 2020 at 10:54):

The first block inserted is the entry block.

osa1 (May 14 2020 at 10:55):

How do I insert a block?

bjorn3 (May 14 2020 at 10:55):

aka the first time you call switch_to_block that block will become the entry block.

osa1 (May 14 2020 at 10:55):

The first block created?

osa1 (May 14 2020 at 10:55):

osa1 (May 14 2020 at 10:57):

I still can't use arguments ...

osa1 (May 14 2020 at 10:57):

variable Variable(12) is used but its type has not been declared

osa1 (May 14 2020 at 10:58):

Hmm

osa1 (May 14 2020 at 10:59):

How do I get Values of the arguments after append_block_params_for_function_params?

bjorn3 (May 14 2020 at 10:59):

Where does Variable(12) come from?

osa1 (May 14 2020 at 10:59):

Ahh! Found ti!

osa1 (May 14 2020 at 10:59):

Thanks @bjorn3

osa1 (May 14 2020 at 11:02):

I'll get the values of args using entry_block.block_params(), right?

osa1 (May 14 2020 at 11:10):

Do I really ahve to invent Variable numbers myself or is there a method in cranelift for that?

osa1 (May 14 2020 at 11:16):

In other words, if I ahve let x = y in my language, do I have to invent a cranelift Variable for that x myself? Any invariants about the u32 for it? (e.g. should variable u32s be consecutive or can I pick 100 for the first var and 123123 for the second?)

osa1 (May 14 2020 at 11:36):

What does this mean: assertion failed: func_ctx.is_empty() ?

osa1 (May 14 2020 at 11:43):

Figured out the func_ctx.is_empty() stuff. Still a bit confused about variables though

osa1 (May 14 2020 at 11:47):

Given a FuncId is there a way to get the signature of the function?

osa1 (May 14 2020 at 11:54):

Welp unimplemented type: types::INVALID ...

osa1 (May 14 2020 at 12:11):

But the good news is I can generate 2 functions before this error :grinning_face_with_smiling_eyes:

bjorn3 (May 14 2020 at 12:19):

osa1 said:

I'll get the values of args using entry_block.block_params(), right?

yes

bjorn3 (May 14 2020 at 12:20):

osa1 said:

In other words, if I ahve let x = y in my language, do I have to invent a cranelift Variable for that x myself? Any invariants about the u32 for it? (e.g. should variable u32s be consecutive or can I pick 100 for the first var and 123123 for the second?)

yes, you can use arbitrary numbers, but the memory usage is proportional to the largest number you choose I believe.

bjorn3 (May 14 2020 at 12:21):

osa1 said:

Given a FuncId is there a way to get the signature of the function?

I don't think so

osa1 (May 14 2020 at 13:39):

OK back at yak shaving -- @bjorn3 do you know what this error means: unimplemented type: types::INVALID

osa1 (May 14 2020 at 13:41):

Happens on seal_block()

osa1 (May 14 2020 at 13:45):

I think I'm not initializing something that I'm supposed to but I don't know what

bjorn3 (May 14 2020 at 14:11):

@osa1 Is there a backtrace?

bjorn3 (May 14 2020 at 14:14):

Probably here: https://github.com/bytecodealliance/wasmtime/blob/0592b5a9956a7f8b51abf79830d3b70521c9aa4d/cranelift/frontend/src/ssa.rs#L206

bytecodealliance/wasmtime

Standalone JIT-style runtime for WebAssembly, using Cranelift - bytecodealliance/wasmtime

bjorn3 (May 14 2020 at 14:16):

Did you call builder.declare_var with the type of the variable before you used it?

osa1 (May 14 2020 at 14:27):

Hmm I think that's the problem, yes. I have some built-in functions (implemented in C), I think I"m not declaring it currently

osa1 (May 14 2020 at 14:27):

Hmm I think that's the problem, yes. I have some built-in functions (implemented in C), I think I"m not declaring it currently

Last updated: Dec 23 2024 at 13:07 UTC