Stop emitting the features section in some buggy cases, in optimized builds (#20409)

wasm-emscripten-finalize strips the features section (after emitting metadata using it),
but we no longer always run that tool, so we need to strip it manually otherwise, at
least in optimized builds (in unoptimized ones, it's just a few more bytes so we don't
bother, as it would slow down the builds).

Author: kripken

emcc.py

@@ -627,6 +627,14 @@ def should_run_binaryen_optimizer():
 def get_binaryen_passes():
   passes = []
   optimizing = should_run_binaryen_optimizer()
+  # wasm-emscripten-finalize will strip the features section for us
+  # automatically, but if we did not modify the wasm then we didn't run it,
+  # and in an optimized build we strip it manually here. (note that in an
+  # unoptimized build we might end up with the features section, if we neither
+  # optimize nor run wasm-emscripten-finalize, but a few extra bytes in the
+  # binary don't matter in an unoptimized build)
+  if optimizing:
+    passes += ['--strip-target-features']
   # safe heap must run before post-emscripten, so post-emscripten can apply the sbrk ptr
   if settings.SAFE_HEAP:
     passes += ['--safe-heap']

test/other/metadce/test_metadce_minimal_64.size

@@ -1 +1 @@
-319
+73

test/other/metadce/test_metadce_minimal_O0.jssize

@@ -1 +1 @@
-19972
+19973

test/other/metadce/test_metadce_minimal_O1.jssize

@@ -1 +1 @@
-4495
+4496

test/test_other.py

@@ -9664,6 +9664,18 @@ def test_wasm_producers_section(self, args):
     size_with_section = os.path.getsize('a.out.wasm')
     self.assertLess(size, size_with_section)
 
+  @parameterized({
+    '':       ([],),
+    # in some modes we skip wasm-emscripten-finalize, which normally strips the
+    # features section for us, so add testing for those
+    'bigint': (['-sWASM_BIGINT'],),
+    'wasm64': (['-sMEMORY64'],),
+  })
+  def test_wasm_features_section(self, args):
+    # The features section should never be in our output, when we optimize.
+    self.run_process([EMCC, test_file('hello_world.c'), '-O2'] + args)
+    self.verify_custom_sec_existence('a.out.wasm', 'target_features', False)
+
   def test_js_preprocess(self):
     # Use stderr rather than stdout here because stdout is redirected to the output JS file itself.
     create_file('lib.js', '''