Allow wasm object files as input, even when WASM_OBJECT_FILES=0 is set (

emscripten-core#8600)

Specifying WASM_OBJECT_FILES=0 on the link line is current needed if
one want to select LTO libraries.  However this should not exclude
some input being wasm object files.

Fixes emscripten-core#8599

emcc.py

@@ -879,9 +879,9 @@ def optimizing(opts):
             has_header_inputs = True
           elif file_suffix.endswith(ASSEMBLY_ENDINGS) or shared.Building.is_bitcode(arg) or shared.Building.is_ar(arg):
             input_files.append((i, arg))
-          elif 'WASM_OBJECT_FILES=0' not in settings_changes and shared.Building.is_wasm(arg):
-            # this is before libraries, since wasm static libraries (wasm.so that contains wasm) are just
-            # object files to be linked
+          elif shared.Building.is_wasm(arg):
+            if not shared.Settings.WASM_BACKEND:
+              exit_with_error('fastcomp is not compatible with wasm object files:' + arg)
             input_files.append((i, arg))
           elif file_suffix.endswith(STATICLIB_ENDINGS + DYNAMICLIB_ENDINGS):
             # if it's not, and it's a library, just add it to libs to find later

src/settings.js

@@ -979,6 +979,8 @@ var WASM_BACKEND = 0;
 
 // Whether to compile object files as wasm as opposed to the default
 // of using LLVM IR.
+// Setting to zero will enable LTO and at link time will also enable bitcode
+// versions of the standard libraries.
 var WASM_OBJECT_FILES = 1;
 
 // An optional comma-separated list of script hooks to run after binaryen,

tests/test_other.py

@@ -8130,24 +8130,39 @@ def test_wasm_targets_side_module(self):
         assert not x.endswith('.js'), 'we should not emit js when making a wasm side module: ' + x
       self.assertIn(b'dylink', open(target, 'rb').read())
 
+  @no_fastcomp('uses upstream specific option: WASM_OBJECT_FILES')
   def test_wasm_backend_lto(self):
     # test building of non-wasm-object-files libraries, building with them, and running them
     if not self.is_wasm_backend():
       self.skipTest('not using wasm backend')
+
+    src = path_from_root('tests', 'hello_libcxx.cpp')
     # test codegen in lto mode, and compare to normal (wasm object) mode
     for args in [[], ['-O1'], ['-O2'], ['-O3'], ['-Os'], ['-Oz']]:
       print(args)
+
       print('wasm in object')
-      run_process([PYTHON, EMCC, path_from_root('tests', 'hello_libcxx.cpp')] + args + ['-c', '-o', 'a.o'])
-      assert shared.Building.is_wasm('a.o') and not shared.Building.is_bitcode('a.o')
+      run_process([PYTHON, EMXX, src] + args + ['-c', '-o', 'hello_obj.o'])
+      self.assertTrue(shared.Building.is_wasm('hello_obj.o'))
+      self.assertFalse(shared.Building.is_bitcode('hello_obj.o'))
+
       print('bitcode in object')
-      run_process([PYTHON, EMCC, path_from_root('tests', 'hello_libcxx.cpp')] + args + ['-c', '-o', 'a.o', '-s', 'WASM_OBJECT_FILES=0'])
-      assert not shared.Building.is_wasm('a.o') and shared.Building.is_bitcode('a.o')
-      print('build bitcode object')
-      run_process([PYTHON, EMCC, 'a.o'] + args + ['-s', 'WASM_OBJECT_FILES=0'])
+      run_process([PYTHON, EMXX, src] + args + ['-c', '-o', 'hello_bitcode.o', '-s', 'WASM_OBJECT_FILES=0'])
+      self.assertFalse(shared.Building.is_wasm('hello_bitcode.o'))
+      self.assertTrue(shared.Building.is_bitcode('hello_bitcode.o'))
+
+      print('use bitcode object (LTO)')
+      run_process([PYTHON, EMXX, 'hello_bitcode.o'] + args + ['-s', 'WASM_OBJECT_FILES=0'])
+      self.assertContained('hello, world!', run_js('a.out.js'))
+      print('use bitcode object (non-LTO)')
+      run_process([PYTHON, EMXX, 'hello_bitcode.o'] + args + ['-s', 'WASM_OBJECT_FILES=1'])
+      self.assertContained('hello, world!', run_js('a.out.js'))
+
+      print('use native object (LTO)')
+      run_process([PYTHON, EMXX, 'hello_obj.o'] + args + ['-s', 'WASM_OBJECT_FILES=0'])
       self.assertContained('hello, world!', run_js('a.out.js'))
-      print('build with bitcode')
-      run_process([PYTHON, EMCC, path_from_root('tests', 'hello_libcxx.cpp')] + args + ['-s', 'WASM_OBJECT_FILES=0'])
+      print('use native object (non-LTO)')
+      run_process([PYTHON, EMXX, 'hello_obj.o'] + args + ['-s', 'WASM_OBJECT_FILES=1'])
       self.assertContained('hello, world!', run_js('a.out.js'))
 
   def test_wasm_nope(self):