Customize the limit of MaxDataSegments

[lorsanta]

Related to #7229.

The custom limit can be passed by doing --pass-arg=limit-segments@1024 .

I didn't commit a unit test because I don't think it's necessary to add one, but I wrote one to test everything works:

index e2468e689..42e696421 100644
--- a/test/unit/test_memory_packing.py
+++ b/test/unit/test_memory_packing.py
@@ -40,3 +40,19 @@ class MemoryPackingTest(utils.BinaryenTestCase):
         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)
+
+    def test_limit_segments_arg(self):
+        max_data_segments = 1024
+        data = '\n'.join('(data (i32.const %i) "A")' % i for i in range(100001))
+        module = '(module (memory 256 256) %s)' % data
+        opts = ['--limit-segments', f'--pass-arg=limit-segments@{max_data_segments}', '--print',
+                '-o', os.devnull]
+        output = [
+            f'(data ${max_data_segments-3} (i32.const {max_data_segments-3}) "A")',
+            f'(data $ (i32.const {max_data_segments-2}) "{"A"*(100001-(max_data_segments-2))}")'
+        ]
+        p = shared.run_process(shared.WASM_OPT + opts, input=module,
+                               check=False, capture_output=True)
+        self.assertEqual(p.returncode, 0)
+        for line in output:
+            self.assertIn(line, p.stdout)

[kripken]

I agree a python unit test is not needed, but let's add a simple lit test. We are in the process of moving more testing to lit.

See e.g. test/lit/passes/strip-eh.wast for an example lit test to base off of. That directory is the right place for it.

[kripken]

lgtm otherwise

[kripken]

Please add a comment documenting this flag, similar to

binaryen/src/passes/Asyncify.cpp

Lines 236 to 240 in 19dd23d

	// --pass-arg=asyncify-asserts
	//
	// This enables extra asserts in the output, like checking if we put in
	// an unwind/rewind in an invalid place (this can be helpful for manual
	// tweaking of the only-list / remove-list, see later).