Compiler configuration with -O or -C/--codegen flag on wasmer

[Hywan]

Considering (i) #1212, (ii) we have multiple backends addressing different needs, (iii) we may add more profiling information or execution context, I'm more and more thinking about adding the very classical compiler -C/--codegen option to the wasmer executable. Here is a list of options I've in mind (inspired from rustc):

• -C opt-level=value where value can be:
  • 0 to 3, where 0 implies --generate-debug-info (introduced in Add support for GDB JIT debugging #1212),
  • s and z to optimise for speed or small size,
  • the option controls the output of the compiler, but we may even use this option to run wasm-opt on the Wasm module before starting compilation, just an idea,
• -C backend-arguments=value where value is different according to the backend:
  • arguments to the LLVM backend (@nick may confirm that it could be useful to enable/disable some passes, checks or assertions),
  • arguments to the Singlepass backend (@losfair may confirm whether it is useful or not),
  • arguments to the Cranelift backend,
• -C overflow-checks=yes/no to check integer overflows,
• -C debuginfo=value where value can be:
  • 0 for no debug info,
  • 1 for line tables only,
  • 2 for full debug information,
• -C profile-generate=value to enable PGO (I assume it can work only with the LLVM backend for the moment, we don't support PGO in Singlepass or Cranelift, cc @nick),
• -C profile-use=value to use a PGO profile file,
• -C target-cpu and target-features to cross-compile or to enable some specific features for a target,
• -C simd=yes/no to replace the --enable-simd option,
• -C thread=yes/no to replace the --enable-thread option,
• -C wasm-features=values to replace the --enable-all features,
• -C abi-arguments=values where value depends on the ABI: emscripten or WASI, even if the current option (--em-entrypoint, --em-symbol-map, --dir etc.) are for runtime only, not compile-time. We should find a way to simplify those options too, that's for another issue.

And thus, we can have the very classical alias option -Ovalue for -C opt-level=value.

I think it is important to get a standard way to configure the backends and the compilations before adding too much options.

Also, it would imply to rethinkg a little bit the wasmer command. For the moment, we have the following commands:

• run to compile and cache (if not cached), and run a module,
• cache to clean the caches,
• validate to validate a module.

Here is my proposal:

• build to compile and cache a module,
• run to compile and cache (if not cached), and run a module,
• cache to clean the caches,
• validate to validate a module.

The new build command will offer the -O and -C options, while run on the other hand will just assume default options and configurations.

Thoughts?

Additional cc @syrusakbary @MarkMcCaskey

[losfair]

I think this is generally a good idea. But instead of having a -C for everything, can we divide the arguments into two classes?

Class 1: High-level features that Wasm programs depend on. wasm-features and (maybe flattened) abi-arguments belong to this class.

Class 2: Low-level details that we can usually figure out a good default value for. Optimization level, overflow checks, debuginfo, target-cpu, PGO, middlewares and most backend-specific options.

For Class 1 they can be assigned first-level arguments for convenience of use, and Class 2 arguments can be put behind -C since they are not frequently used.

[MarkMcCaskey]

I agree with @losfair here and like the idea of having finer grained options exposed to user generally!

I'm for this change with the qualifications mentioned!

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Hywan]

Still relevant.

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

Feel free to reopen the issue if it has been closed by mistake.