WIP: Add support for the llvm: use scheme

[redvers]

In the ponysync meeting on 2021-11-02 and on Zulip we discussed having a use scheme which would allow inclusion and linking of pre-generated llvm-ir (.ll) files by the ponyc compiler.

@jemc walked me through compiler and the process needed to make these changes and this is the result thus far.

Here is how it works:

use "llvm:addints"
use @addints[I32](a: I32, b: I32)

actor Main
  new create(env: Env) =>
    let x: I32 = @addints(I32(10), I32(32))
    env.out.print("Got: " + x.string())

The use scheme makes ponyc look for the associated file.ll, so in the above example: addints.ll

To generate the addints.ll file, we take the following C file:

int addints(int a, int b) {return a + b;};

… and compile like so:

[nix-shell:~/projects/ponyc]$ clang -emit-llvm -S addints.c
[nix-shell:~/projects/ponyc]$ head addints.ll
; ModuleID = 'addints.c'
source_filename = "addints.c"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

; Function Attrs: norecurse nounwind readnone sspstrong uwtable
define i32 @addints(i32, i32) local_unnamed_addr #0 {
  %3 = add i32 %1, %0
  ret i32 %3
}

Pony compilation and execution:

[nix-shell:~/projects/ponyc]$ ./build/debug/ponyc
Building builtin -> /home/red/projects/ponyc/packages/builtin
Building . -> /home/red/projects/ponyc
Generating
 Reachability
 Selector painting
 Data prototypes
 Data types
 Function prototypes
 Functions
 Descriptors
Optimising
warning: Linking two modules of different data layouts: '/home/red/projects/ponyc/addints.ll' is 'e-m:e-i64:64-f80:128-n8:16:32:64-S128' whereas 'ponyc' is 'e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128'

Writing ./ponyc.o
Linking ./ponyc

[nix-shell:~/projects/ponyc]$ ./ponyc 
Got: 42

TODO:
[] Initial Code Review
[] Write Tests
[] Ensure that .ll files from other packages resolve to the correct path
[] Write an example
[] Tutorial Updates
[] Identify if the above warning is NixOS specific and understand what it means.
[] TWIP

Please let me know if I've missed anything.

Thanks,

Red

[SeanTAllen]

@redvers have you done any more work on this?