minifier: alpha release

[camc314]

Tracking a range of misc minifier improvements vs esbuild

• 1. minify function invokaction syntax when spreading an empty array: feat(minifier): flatten spread args in call expressions #8266

import("./empty_FIXTURE.js")(...[])  
import("./empty_FIXTURE.js")()  

• 3. computed getter definitions in object literals

obj = { get[8]() { return "get string" } }  
obj = { get 8() { return "get string" } }  

• 4. computed numeric property access to objects. NOTE: although esbuild performs this optimization, it may not be safe

obj["8"]  
obj[8]  

5. remove unneccessary labels

• 6. Use Exponential Notation for Large Numbers

1000000000.5  
1e9 + .5 

7. inline single use const

const str = "1970-01-01[+00:00]";  
assert.sameValue(instance.equals(str))  
assert.sameValue(instance.equals("1970-01-01[+00:00]"))  

• 8. normalize nullish comparisons

foo != undefined  
foo != null  

• 9.

var x = () => !!delete foo;  
var x = () => delete foo;  

[Boshen]

I want to stabilize an alpha version this week, which consists of safe peephole optimizations, some refactorings, test clean up and documentation.

This leaves out:

• inlining (7. inline single use const)
• dead code removal (5. remove unneccessary labels)

[Boshen]

Current implementation of is_in_boolean_context is too hard to track, I may reimplement it by calling it on known boolean context positions, similar to how esbuild does it.

[Boshen]

It seems like most peephole optimizations are done, time to stabilize:

• port some of the remaining minimize condition logic from esbuild
  • mangleStmts https://github.com/evanw/esbuild/blob/v0.24.2/internal/js_parser/js_parser.go#L8788
  • MangleIfExpr https://github.com/evanw/esbuild/blob/v0.24.2/internal/js_ast/js_ast_helpers.go#L2745
  • SimplifyBooleanExpr https://github.com/evanw/esbuild/blob/v0.24.2/internal/js_ast/js_ast_helpers.go#L2059
• refactor code
• improve performance
• fix broken test cases in monitor-oxc

---

Note: esbuild has a "bug" regarding constant folding multiplication, division and exponential - https://github.com/evanw/esbuild/blob/df815ac27b84f8b34374c9182a93c94718f8a630/internal/js_parser/js_parser.go#L10369-L10380

It "accidently" or "unintentially" folded more than it should, which lead to a bit of unstableness 😅

[camc314]

i am going to try port mangleStmts today/tommorow

mangleStmts

https://github.com/evanw/esbuild/blob/v0.24.2/internal/js_ast/js_ast_helpers.go#L2745

• Remove Inlined Constants:
  • TODO
• Control Flow Optimization:
  • Done:

    oxc/crates/oxc_minifier/src/ast_passes/peephole_remove_dead_code.rs

    Line 76 in 6c7acac

    fn dead_code_elimination(&mut self, stmts: &mut Vec<'a, Statement<'a>>, ctx: Ctx<'a, 'b>) {

• Variable Inlining:
  • TODO
• Statement Merging:
  • Done:

    oxc/crates/oxc_minifier/src/ast_passes/statement_fusion.rs

    Line 36 in 772b71c

    fn fuse_statements(&mut self, stmts: &mut Vec<'a, Statement<'a>>, ctx: &mut TraverseCtx<'a>) {

• Control Flow Simplification:
  • initial impl done, but buggy: refactor(minifier): remove the buggy minimize_exit_points implementation #8349
• Trailing Jump Optimization:
  • TODO: continue/return/break stmts at the end of control flow are dropped
• Try-Catch Simplification:
  • Done

    oxc/crates/oxc_minifier/src/ast_passes/peephole_substitute_alternate_syntax.rs

    Line 191 in 772b71c

    fn compress_catch_clause(&mut self, catch: &mut CatchClause<'_>, ctx: &mut TraverseCtx<'a>) {

• Switch and For Loop Transformations:
  • TODO

[Boshen]

@camc314 Thank you.

Can we hold onto the the larger changes such as control flow optimizations and inlinings? Things get difficult when state tracking is required. But you may start implementing them, I won't be able to merge them until I stabilize everything else.