Move segment merging to fit web limits into its own pass (#1980)

It was previously part of writing a binary, but changing the number of
segments at such a late stage would not work in the presence of bulk
memory's datacount section. Also updates the memory packing pass
to respect the web's limits on the number of data segments.

1 files changed, 40 insertions, 0 deletions

diff --git a/test/unit/test_memory_packing.py b/test/unit/test_memory_packing.py
new file mode 100644
index 000000000..0d62b0ed5
--- /dev/null
+++ b/test/unit/test_memory_packing.py
@@ -0,0 +1,40 @@
+import os
+import unittest
+from scripts.test.shared import WASM_OPT, run_process
+
+'''Test that MemoryPacking correctly respects the web limitations by not
+generating more than 100K data segments'''
+
+
+class MemoryPackingTest(unittest.TestCase):
+  def test_large_segment(self):
+    data = '"' + (('A' + ('\\00' * 9)) * 100001) + '"'
+    module = '''
+    (module
+     (memory 256 256)
+     (data (i32.const 0) %s)
+    )
+    ''' % data
+    opts = ['--memory-packing', '--disable-bulk-memory', '--print',
+            '-o', os.devnull]
+    p = run_process(WASM_OPT + opts, input=module, check=False,
+                    capture_output=True)
+    output = [
+        '(data (i32.const 999970) "A")',
+        '(data (i32.const 999980) "A")',
+        '(data (i32.const 999990) "A' + ('\\00' * 9) + 'A")'
+    ]
+    self.assertEqual(p.returncode, 0)
+    for line in output:
+      self.assertIn(line, p.stdout)
+
+  def test_large_segment_unmergeable(self):
+    data = '\n'.join('(data (i32.const %i) "A")' % i for i in range(100001))
+    module = '(module (memory 256 256) %s)' % data
+    opts = ['--memory-packing', '--enable-bulk-memory', '--print',
+            '-o', os.devnull]
+    p = run_process(WASM_OPT + opts, input=module, check=False,
+                    capture_output=True)
+    self.assertEqual(p.returncode, 0)
+    self.assertIn('Some VMs may not accept this binary', p.stderr)
+    self.assertIn('Run the limit-segments pass to merge segments.', p.stderr)