Fix bulk memory feature removal in optimizing builds

test/test_other.py

@@ -9974,6 +9974,23 @@ def compile(flags):
     compile(['-sMIN_SAFARI_VERSION=140100', '-mbulk-memory'])
     verify_features_sec_linked('nontrapping-fptoint', False)
 
+  def test_no_bulk_memory(self):
+    # The test_wasm_features test (above) uses the feature section to confirm
+    # if a feature is present, but that doesn't work in optimizing builds
+    # since we strip the feature section in release builds.
+    # This test confirms that no DATACOUNT section is present in the final
+    # binary.
+
+    def has_data_count(filename):
+      with webassembly.Module(filename) as wasm:
+        return wasm.get_section(webassembly.SecType.DATACOUNT)
+
+    self.emcc('hello_world.c', ['-O3', '-o', 'bulk.js'])
+    self.assertTrue(has_data_count('bulk.wasm'))
+
+    self.emcc('hello_world.c', ['-O3', '-o', 'nobulk.js', '-mno-bulk-memory', '-mno-bulk-memory-opt'])
+    self.assertFalse(has_data_count('nobulk.wasm'))
+
   @crossplatform
   def test_html_preprocess(self):
     src_file = test_file('module/test_stdin.c')

tools/link.py

@@ -34,6 +34,7 @@
   webassembly,
 )
 from .cmdline import OFormat
+from .feature_matrix import Feature
 from .minimal_runtime_shell import generate_minimal_runtime_html
 from .settings import (
   DEPRECATED_SETTINGS,
@@ -367,16 +368,21 @@ def get_binaryen_lowering_passes():
   # This can happen if the feature is explicitly disabled on the command line,
   # or when targeting an VM/engine that does not support the feature.
 
-  # List of [<feature_name>, <lowering_flag>] pairs.
+  # List of [<feature_name>, <lowering_flag>, <feature_flags>] triples.
   features = [
-    [feature_matrix.Feature.SIGN_EXT, '--signext-lowering'],
-    [feature_matrix.Feature.NON_TRAPPING_FPTOINT, '--llvm-nontrapping-fptoint-lowering'],
-    [feature_matrix.Feature.BULK_MEMORY, '--llvm-memory-copy-fill-lowering'],
+    [Feature.SIGN_EXT, '--signext-lowering', ['--enable-sign-ext']],
+    [Feature.NON_TRAPPING_FPTOINT, '--llvm-nontrapping-fptoint-lowering', ['--enable-nontrapping-float-to-int']],
+    [Feature.BULK_MEMORY, '--llvm-memory-copy-fill-lowering', ['--enable-bulk-memory', '--enable-bulk-memory-opt']],
   ]
 
-  for feature, lowering_flag in features:
+  for feature, lowering_flag, feature_flags in features:
     if not feature_matrix.caniuse(feature):
       logger.debug(f'lowering {feature.name} feature due to incompatible target browser engines')
+      for f in feature_flags:
+        # Remove features from binaryen_features, otherwise future runs of binaryen
+        # could re-introduce the feature.
+        if f in building.binaryen_features:
+          building.binaryen_features.remove(f)
       passes.append(lowering_flag)
 
   return passes
@@ -1044,7 +1050,7 @@ def limit_incoming_module_api():
     if user_settings.get('WASM_BIGINT') and settings.WASM_BIGINT:
       exit_with_error('WASM_BIGINT=1 is not compatible with wasm2js')
     settings.WASM_BIGINT = 0
-    feature_matrix.disable_feature(feature_matrix.Feature.JS_BIGINT_INTEGRATION)
+    feature_matrix.disable_feature(Feature.JS_BIGINT_INTEGRATION)
 
   if options.oformat == OFormat.WASM and not settings.SIDE_MODULE:
     # if the output is just a wasm file, it will normally be a standalone one,
@@ -1583,8 +1589,8 @@ def limit_incoming_module_api():
 
   # TODO(sbc): Find make a generic way to expose the feature matrix to JS
   # compiler rather then adding them all ad-hoc as internal settings
-  settings.SUPPORTS_PROMISE_ANY = feature_matrix.caniuse(feature_matrix.Feature.PROMISE_ANY)
-  default_setting('WASM_BIGINT', feature_matrix.caniuse(feature_matrix.Feature.JS_BIGINT_INTEGRATION))
+  settings.SUPPORTS_PROMISE_ANY = feature_matrix.caniuse(Feature.PROMISE_ANY)
+  default_setting('WASM_BIGINT', feature_matrix.caniuse(Feature.JS_BIGINT_INTEGRATION))
 
   if settings.AUDIO_WORKLET:
     add_system_js_lib('libwebaudio.js')