Basic support of asm.js uglification

[vibornoff]

A had a problem when trying to uglify asm.js modules in my asmcrypto.js project.

To fix that issue I added basic support:

• Asm.js is turned on by directive "use asm", so when it is met,
• Name mangler doesn't reuse names in the inner scopes of the modules, and
• Compression is turned off for that modules.

[mishoo]

Note that has_directive returns the scope where the directive is found (so it looks into the parent scope too), therefore if the directive is specified on the parent then: this.has_directive("use asm") == this.parent_scope.has_directive("use asm");

[vibornoff]

Take a closer look: pasm is set to true only if the current scope is nested into the asm scope.
So it's false for top-level asm scope even it has "use asm" directive.

[mishoo]

OK. It's just that it's unclear to me what this whole patch does, can you explain in plain English?

My understanding is that you need to not shadow the name of the function where "use asm" is found, is that all?

[vibornoff]

what this whole patch does, can you explain in plain English?

Sorry, my fault.

Asm.js — is a highly optimizable and restricted subset of JavaScript. For more information take a look into Wikipedia article and latest Asm.js specification. It's in heavy development now and available only in Firefox (>= 22).

This patch attempts to add basic support of asm.js handling into your project as UglifyJS2 doesn't know anything about asm.js and when I feed valid asm.js code it produces invalid uglified output (though output remains valid JS code).

My understanding is that you need to not shadow the name of the function where "use asm" is found, is that all?

There is a number of issues:

• internal scopes of asm.js module can't overload names existing in the top-level asm.js scope
• (seems bug of asm.js implementation) name of the module can't be reused inside although it is out of the module scope
• any optimization have to be bypassed exept maybe drop_unused since asm.js has different typing paradigm (see spec)

Also asm.js have its own validation rules but they are out of the scope of this project since it is for general-purpose JavaScript. My patch is focused on making UglifyJS2 not to produce invalid asm.js code when valid is supplied.

[vibornoff]

Rebased

[vibornoff]

Up

[pohutukawa]

It would be really nice if asm.js support was provided out of the box by UglifyJS2. It can be a real stopper for automatic deployment of JS modules via npm using the dependencies in package.json.

[bored-engineer]

Bump

[avdg]

I am wondering why this ticket is still being open. However given the comments in the patches, I guess we need a separate maintainer for the asm module with someone who knows asm.js better (just take this as a proposal, other ideas are welcome).

I am not sure if that's doable and/or its something that @mishoo wants.

Comments?

[diegocr]

+1 -- Bump

[vibornoff]

Just rebased my old commits with few minor modifications

[rvanvelzen]

This is probably outdated, so I'm closing this PR. Feel free to re-submit if you think it should be merged.