Extend support for -### flag to optimized linking (emscripten-core#22877)

This will cause the ### flag to print most Binaryen and acorn-optimizer
subcommands in addtion to clang and ld. However accuracy isn't perfect
because some steps (E.g. metadce) depend on the output of previous
steps.

Author: dschuff

test/test_other.py

@@ -321,9 +321,11 @@ def test_log_subcommands(self):
 
   def test_skip_subcommands(self):
     # The -### flag is like `-v` but it doesn't actaully execute the sub-commands
-    proc = self.run_process([EMCC, '-###', test_file('hello_world.c')], stdout=PIPE, stderr=PIPE)
+    proc = self.run_process([EMCC, '-###', '-O3', test_file('hello_world.c')], stdout=PIPE, stderr=PIPE)
     self.assertContained(CLANG_CC, proc.stderr)
     self.assertContained(WASM_LD, proc.stderr)
+    self.assertContained('wasm-opt', proc.stderr)
+    self.assertContained('acorn-optimizer.mjs', proc.stderr)
     self.assertNotExists('a.out.js')
 
   def test_emcc_check(self):

tools/building.py

@@ -348,7 +348,7 @@ def js_optimizer(filename, passes):
 def acorn_optimizer(filename, passes, extra_info=None, return_output=False, worker_js=False):
   optimizer = path_from_root('tools/acorn-optimizer.mjs')
   original_filename = filename
-  if extra_info is not None:
+  if extra_info is not None and not shared.SKIP_SUBPROCS:
     temp_files = shared.get_temp_files()
     temp = temp_files.get('.js', prefix='emcc_acorn_info_').name
     shutil.copyfile(filename, temp)
@@ -366,6 +366,9 @@ def acorn_optimizer(filename, passes, extra_info=None, return_output=False, work
   if settings.VERBOSE:
     cmd += ['--verbose']
   if return_output:
+    shared.print_compiler_stage(cmd)
+    if shared.SKIP_SUBPROCS:
+      return ''
     return check_call(cmd, stdout=PIPE).stdout
 
   acorn_optimizer.counter += 1
@@ -375,6 +378,9 @@ def acorn_optimizer(filename, passes, extra_info=None, return_output=False, work
   output_file = basename + '.jso%d.js' % acorn_optimizer.counter
   shared.get_temp_files().note(output_file)
   cmd += ['-o', output_file]
+  shared.print_compiler_stage(cmd)
+  if shared.SKIP_SUBPROCS:
+    return output_file
   check_call(cmd)
   save_intermediate(output_file, '%s.js' % passes[0])
   return output_file
@@ -780,6 +786,9 @@ def metadce(js_file, wasm_file, debug_info, last):
   extra_info = '{ "exports": [' + ','.join(f'["{asmjs_mangle(x)}", "{x}"]' for x in exports) + ']}'
 
   txt = acorn_optimizer(js_file, ['emitDCEGraph', '--no-print'], return_output=True, extra_info=extra_info)
+  if shared.SKIP_SUBPROCS:
+    # The next steps depend on the output from this step, so we can't do them if we aren't actually running.
+    return js_file
   graph = json.loads(txt)
   # ensure that functions expected to be exported to the outside are roots
   required_symbols = user_requested_exports.union(set(settings.SIDE_MODULE_IMPORTS))
@@ -1209,6 +1218,9 @@ def run_binaryen_command(tool, infile, outfile=None, args=None, debug=False, std
   if settings.GENERATE_SOURCE_MAP and outfile and tool in ['wasm-opt', 'wasm-emscripten-finalize']:
     cmd += [f'--input-source-map={infile}.map']
     cmd += [f'--output-source-map={outfile}.map']
+  shared.print_compiler_stage(cmd)
+  if shared.SKIP_SUBPROCS:
+    return ''
   ret = check_call(cmd, stdout=stdout).stdout
   if outfile:
     save_intermediate(outfile, '%s.wasm' % tool)