Convert unsafe_optimizations.js to mjs. NFC (#21504)

Author: sbc100

test/test_other.py

@@ -13547,7 +13547,7 @@ def test_clock_nanosleep(self):
 
   # Tests the internal test suite of tools/unsafe_optimizations.js
   def test_unsafe_optimizations(self):
-    self.run_process(config.NODE_JS_TEST + [path_from_root('tools', 'unsafe_optimizations.js'), '--test'])
+    self.run_process(config.NODE_JS_TEST + [path_from_root('tools', 'unsafe_optimizations.mjs'), '--test'])
 
   @requires_v8
   def test_extended_const(self):

tools/link.py

@@ -2075,15 +2075,15 @@ def phase_final_emitting(options, state, target, wasm_target):
   # optimize by Closure, or unoptimalities that were left behind by processing
   # steps that occurred after Closure.
   if settings.MINIMAL_RUNTIME == 2 and settings.USE_CLOSURE_COMPILER and settings.DEBUG_LEVEL == 0:
-    shared.run_js_tool(utils.path_from_root('tools/unsafe_optimizations.js'), [final_js, '-o', final_js], cwd=utils.path_from_root('.'))
+    shared.run_js_tool(utils.path_from_root('tools/unsafe_optimizations.mjs'), [final_js, '-o', final_js], cwd=utils.path_from_root('.'))
     save_intermediate('unsafe-optimizations')
     # Finally, rerun Closure compile with simple optimizations. It will be able
     # to further minify the code. (n.b. it would not be safe to run in advanced
     # mode)
     final_js = building.closure_compiler(final_js, advanced=False, extra_closure_args=options.closure_args)
     # Run unsafe_optimizations.js once more.  This allows the cleanup of newly
     # unused things that closure compiler leaves behind (e.g `new Float64Array(x)`).
-    shared.run_js_tool(utils.path_from_root('tools/unsafe_optimizations.js'), [final_js, '-o', final_js], cwd=utils.path_from_root('.'))
+    shared.run_js_tool(utils.path_from_root('tools/unsafe_optimizations.mjs'), [final_js, '-o', final_js], cwd=utils.path_from_root('.'))
     save_intermediate('unsafe-optimizations2')
 
   fix_es6_import_statements(final_js)

tools/unsafe_optimizations.js renamed to tools/unsafe_optimizations.mjs

@@ -3,11 +3,9 @@
 /** Implements a set of potentially unsafe JavaScript AST optimizations for aggressive code size optimizations.
     Enabled when building with -sMINIMAL_RUNTIME=2 linker flag. */
 
-'use strict';
-
-const acorn = require('acorn');
-const fs = require('fs');
-const terser = require('../third_party/terser/terser');
+import * as fs from 'fs';
+import * as acorn from 'acorn';
+import * as terser from '../third_party/terser/terser.js';
 
 // Starting at the AST node 'root', calls the given callback function 'func' on all children and grandchildren of 'root'
 // that are of any of the type contained in array 'types'.