Add implicit wasm feature disabling based on min browser versions

llvm and binaryen now default to enabling sign-ext and mutable-globals
by default. See https://reviews.llvm.org/D125728.

In order to allow users to continue to target older browsers we will
now lower sign-ext operations in a binaryen pass if the target browsers
don't support it.

emcc.py

@@ -51,6 +51,7 @@
 from tools import wasm2c
 from tools import webassembly
 from tools import config
+from tools import feature_matrix
 from tools.settings import user_settings, settings, MEM_SIZE_SETTINGS, COMPILE_TIME_SETTINGS
 from tools.utils import read_file, write_file, read_binary, delete_file
 
@@ -613,6 +614,13 @@ def get_binaryen_passes():
     passes += ['--safe-heap']
   if settings.MEMORY64 == 2:
     passes += ['--memory64-lowering']
+  # sign-ext is enabled by default by llvm.  If the target browser settings don't support
+  # this we lower it away here using a binaryen pass.
+  if not feature_matrix.caniuse(feature_matrix.Feature.SIGN_EXT):
+    logger.debug('lowering sign-ext proposal due to incompatiable target browser engines')
+    passes += ['--signext-lowering']
+  if settings.MEMORY64 == 2:
+    passes += ['--memory64-lowering']
   if optimizing:
     passes += ['--post-emscripten']
   if optimizing:

test/other/test_signext_lowering.c

@@ -0,0 +1,6 @@
+#include <stdio.h>
+#include <stdint.h>
+
+int main(int argc, char* argv[]) {
+  printf("%lld\n", (int64_t)argc);
+}

test/test_other.py

@@ -12724,3 +12724,22 @@ def test_reproduce(self):
     response = response.replace('\\', '/')
     response = response.replace(root, '<root>')
     self.assertTextDataIdentical(expected, response)
+
+  def test_signext_lowering(self):
+    cmd = [EMCC, test_file('other/test_signext_lowering.c'), '-sWASM_BIGINT', '-sMIN_EDGE_VERSION=0x7fffffff']
+
+    # We expect ERROR_ON_WASM_CHANGES_AFTER_LINK to fail due lowering of sign-ext being
+    # required for safary 12.
+    output = self.expect_fail(cmd + ['-sERROR_ON_WASM_CHANGES_AFTER_LINK', '-sMIN_SAFARI_VERSION=120000'])
+    self.assertContained('error: changes to the wasm are required after link, but disallowed by ERROR_ON_WASM_CHANGES_AFTER_LINK', output)
+    self.assertContained('--signext-lowering', output)
+
+    # Running the same command with safary 14.1 should succeed because no lowering
+    # is required.
+    self.run_process(cmd + ['-sERROR_ON_WASM_CHANGES_AFTER_LINK', '-sMIN_SAFARI_VERSION=140100'])
+    self.assertEqual('1\n', self.run_js('a.out.js'))
+
+    # Running without ERROR_ON_WASM_CHANGES_AFTER_LINK but with safari 12
+    # should successfully lower sign-ext.
+    self.run_process(cmd + ['-sMIN_SAFARI_VERSION=120000', '-o', 'lowered.js'])
+    self.assertEqual('1\n', self.run_js('lowered.js'))

tools/feature_matrix.py

@@ -0,0 +1,60 @@
+# Copyright 2022 The Emscripten Authors.  All rights reserved.
+# Emscripten is available under two separate licenses, the MIT license and the
+# University of Illinois/NCSA Open Source License.  Both these licenses can be
+# found in the LICENSE file.
+
+"""Utilities for mapping browser versions to webassembly features."""
+
+import logging
+from enum import IntEnum, auto
+
+from .settings import settings
+
+logger = logging.getLogger('feature_matrix')
+
+
+class Feature(IntEnum):
+  NON_TRAPPING_FPTOINT = auto()
+  SIGN_EXT = auto()
+  BULK_MEMORY = auto()
+  MUTABLE_GLOBALS = auto()
+
+
+default_features = {Feature.SIGN_EXT, Feature.MUTABLE_GLOBALS}
+
+min_browser_versions = {
+  Feature.NON_TRAPPING_FPTOINT: {
+    'chrome': 75,
+    'firefox': 65,
+    'safari': 150000,
+  },
+  Feature.SIGN_EXT: {
+    'chrome': 74,
+    'firefox': 62,
+    'safari': 140100,
+  },
+  Feature.BULK_MEMORY: {
+    'chrome': 75,
+    'firefox': 79,
+    'safari': 150000,
+  },
+  Feature.MUTABLE_GLOBALS: {
+    'chrome': 74,
+    'firefox': 61,
+    'safari': 120000,
+  },
+}
+
+
+def caniuse(feature):
+  min_versions = min_browser_versions[feature]
+  if settings.MIN_CHROME_VERSION < min_versions['chrome']:
+    return False
+  if settings.MIN_FIREFOX_VERSION < min_versions['firefox']:
+    return False
+  if settings.MIN_SAFARI_VERSION < min_versions['safari']:
+    return False
+  # IE and Edge don't support any non-MVP features
+  if settings.MIN_IE_VERSION != 0x7FFFFFFF or settings.MIN_EDGE_VERSION != 0x7FFFFFFF:
+    return False
+  return True