[emcc.py] Simplify passing arguments to clang in compile-only mode (emscripten-core#23454)

This change avoids removing the `-o` flag and the input files when only
compiling. We delay the splitting out of the linker flags and the input
files until we know actually do to do linking.

This effect of this is that the compile-only phase is now much simply
because it doesn't need to re-inject the input files and the `-o` flag.

This also as the effect of keeping the order of those flags preserved
with respect to other command line flags when calling clang to do
compilation.

Author: sbc100

emcc.py

@@ -139,6 +139,7 @@ class EmccOptions:
   def __init__(self):
     self.target = ''
     self.output_file = None
+    self.input_files = []
     self.no_minify = False
     self.post_link = False
     self.save_temps = False
@@ -659,21 +660,23 @@ def run(args):
   # settings until we reach the linking phase.
   settings.limit_settings(COMPILE_TIME_SETTINGS)
 
-  newargs, input_files = phase_setup(options, state, newargs)
+  phase_setup(options, state, newargs)
 
   if options.reproduce:
     create_reproduce_file(options.reproduce, args)
 
   if state.mode == Mode.POST_LINK_ONLY:
-    if len(input_files) != 1:
+    if len(options.input_files) != 1:
       exit_with_error('--post-link requires a single input file')
+    separate_linker_flags(options, state, newargs)
     # Delay import of link.py to avoid processing this file when only compiling
     from tools import link
-    link.run_post_link(input_files[0][1], options, state)
+    link.run_post_link(options.input_files[0], options, state)
     return 0
 
-  ## Compile source code to object files
-  linker_inputs = phase_compile_inputs(options, state, newargs, input_files)
+  # Compile source code to object files
+  # When only compiling this function never returns.
+  linker_inputs = phase_compile_inputs(options, state, newargs)
 
   if state.mode == Mode.COMPILE_AND_LINK:
     # Delay import of link.py to avoid processing this file when only compiling
@@ -711,11 +714,13 @@ def phase_parse_arguments(state):
     settings.WARN_DEPRECATED = 0
 
   for i in range(len(newargs)):
-    if newargs[i] in ('-l', '-L', '-I', '-z', '--js-library'):
+    if newargs[i] in ('-l', '-L', '-I', '-z', '--js-library', '-o'):
       # Scan for flags that can be written as either one or two arguments
       # and normalize them to the single argument form.
       if newargs[i] == '--js-library':
         newargs[i] += '='
+      if len(newargs) <= i + 1:
+        exit_with_error(f"option '{newargs[i]}' requires an argument")
       newargs[i] += newargs[i + 1]
       newargs[i + 1] = ''
 
@@ -748,10 +753,8 @@ def phase_parse_arguments(state):
   return options, newargs
 
 
-@ToolchainProfiler.profile_block('setup')
-def phase_setup(options, state, newargs):
-  """Second phase: configure and setup the compiler based on the specified settings and arguments.
-  """
+def separate_linker_flags(options, state, newargs):
+  newargs = list(newargs)
 
   if settings.RUNTIME_LINKED_LIBS:
     newargs += settings.RUNTIME_LINKED_LIBS
@@ -769,7 +772,6 @@ def phase_setup(options, state, newargs):
   # based on a full understanding of gcc params, right now we just assume that
   # what is left contains no more |-x OPT| things
   skip = False
-  has_header_inputs = False
   for i in range(len(newargs)):
     if skip:
       skip = False
@@ -792,10 +794,9 @@ def get_next_arg():
       # https://bugs.python.org/issue1311
       if not os.path.exists(arg) and arg != os.devnull:
         exit_with_error('%s: No such file or directory ("%s" was expected to be an input file, based on the commandline arguments provided)', arg, arg)
-      file_suffix = get_file_suffix(arg)
-      if file_suffix in HEADER_ENDINGS:
-        has_header_inputs = True
       input_files.append((i, arg))
+    elif arg.startswith('-o'):
+      newargs[i] = ''
     elif arg.startswith('-L'):
       state.add_link_flag(i, arg)
     elif arg.startswith('-l'):
@@ -824,9 +825,15 @@ def get_next_arg():
 
   newargs = [a for a in newargs if a]
 
-  # SSEx is implemented on top of SIMD128 instruction set, but do not pass SSE flags to LLVM
-  # so it won't think about generating native x86 SSE code.
-  newargs = [x for x in newargs if x not in SIMD_INTEL_FEATURE_TOWER and x not in SIMD_NEON_FLAGS]
+  return newargs, input_files
+
+
+@ToolchainProfiler.profile_block('setup')
+def phase_setup(options, state, newargs):
+  """Second phase: configure and setup the compiler based on the specified settings and arguments.
+  """
+
+  has_header_inputs = any(get_file_suffix(f) in HEADER_ENDINGS for f in options.input_files)
 
   if options.post_link:
     state.mode = Mode.POST_LINK_ONLY
@@ -928,8 +935,6 @@ def get_next_arg():
   if settings.USE_SDL == 2 or settings.USE_SDL_MIXER == 2 or settings.USE_SDL_GFX == 2:
     default_setting('GL_ENABLE_GET_PROC_ADDRESS', 1)
 
-  return (newargs, input_files)
-
 
 def filter_out_link_flags(args):
   rtn = []
@@ -954,7 +959,7 @@ def is_link_flag(flag):
 
 
 @ToolchainProfiler.profile_block('compile inputs')
-def phase_compile_inputs(options, state, compile_args, input_files):
+def phase_compile_inputs(options, state, newargs):
   if shared.run_via_emxx:
     compiler = [shared.CLANG_CXX]
   else:
@@ -978,24 +983,21 @@ def get_language_mode(args):
         return removeprefix(item, '-x')
     return ''
 
-  language_mode = get_language_mode(compile_args)
+  language_mode = get_language_mode(newargs)
   use_cxx = 'c++' in language_mode or shared.run_via_emxx
 
   def get_clang_command():
-    return compiler + get_cflags(state.orig_args, use_cxx) + compile_args
+    return compiler + get_cflags(state.orig_args, use_cxx)
 
   def get_clang_command_preprocessed():
-    return compiler + get_clang_flags(state.orig_args) + compile_args
+    return compiler + get_clang_flags(state.orig_args)
 
   def get_clang_command_asm():
-    return compiler + get_target_flags() + compile_args
+    return compiler + get_target_flags()
 
   # preprocessor-only (-E/-M) support
   if state.mode == Mode.PREPROCESS_ONLY:
-    inputs = [i[1] for i in input_files]
-    cmd = get_clang_command() + inputs
-    if options.output_file:
-      cmd += ['-o', options.output_file]
+    cmd = get_clang_command() + newargs
     # Do not compile, but just output the result from preprocessing stage or
     # output the dependency rule. Warning: clang and gcc behave differently
     # with -MF! (clang seems to not recognize it)
@@ -1005,34 +1007,26 @@ def get_clang_command_asm():
 
   # Precompiled headers support
   if state.mode == Mode.PCH:
-    inputs = [i[1] for i in input_files]
-    for header in inputs:
-      if shared.suffix(header) not in HEADER_ENDINGS:
-        exit_with_error(f'cannot mix precompiled headers with non-header inputs: {inputs} : {header}')
-    cmd = get_clang_command() + inputs
-    if options.output_file:
-      cmd += ['-o', options.output_file]
+    cmd = get_clang_command() + newargs
     logger.debug(f"running (for precompiled headers): {cmd[0]} {' '.join(cmd[1:])}")
     shared.exec_process(cmd)
     assert False, 'exec_process does not return'
 
   if state.mode == Mode.COMPILE_ONLY:
-    inputs = [i[1] for i in input_files]
-    if all(get_file_suffix(i) in ASSEMBLY_ENDINGS for i in inputs):
-      cmd = get_clang_command_asm() + inputs
+    if options.output_file and get_file_suffix(options.output_file) == '.bc' and not settings.LTO and '-emit-llvm' not in state.orig_args:
+      diagnostics.warning('emcc', '.bc output file suffix used without -flto or -emit-llvm.  Consider using .o extension since emcc will output an object file, not a bitcode file')
+    if all(get_file_suffix(i) in ASSEMBLY_ENDINGS for i in options.input_files):
+      cmd = get_clang_command_asm() + newargs
     else:
-      cmd = get_clang_command() + inputs
-    if options.output_file:
-      cmd += ['-o', options.output_file]
-      if get_file_suffix(options.output_file) == '.bc' and not settings.LTO and '-emit-llvm' not in state.orig_args:
-        diagnostics.warning('emcc', '.bc output file suffix used without -flto or -emit-llvm.  Consider using .o extension since emcc will output an object file, not a bitcode file')
+      cmd = get_clang_command() + newargs
     shared.exec_process(cmd)
     assert False, 'exec_process does not return'
 
   # In COMPILE_AND_LINK we need to compile source files too, but we also need to
   # filter out the link flags
   assert state.mode == Mode.COMPILE_AND_LINK
   assert not options.dash_c
+  compile_args, input_files = separate_linker_flags(options, state, newargs)
   compile_args = filter_out_link_flags(compile_args)
   linker_inputs = []
   seen_names = {}
@@ -1057,7 +1051,7 @@ def compile_source_file(i, input_file):
       cmd = get_clang_command()
       if get_file_suffix(input_file) in ['.pcm']:
         cmd = [c for c in cmd if not c.startswith('-fprebuilt-module-path=')]
-    cmd += ['-c', input_file, '-o', output_file]
+    cmd += compile_args + ['-c', input_file, '-o', output_file]
     if state.mode == Mode.COMPILE_AND_LINK and options.requested_debug == '-gsplit-dwarf':
       # When running in COMPILE_AND_LINK mode we compile to temporary location
       # but we want the `.dwo` file to be generated in the current working directory,
@@ -1481,11 +1475,8 @@ def consume_arg_file():
       options.shared = True
     elif check_flag('-r'):
       options.relocatable = True
-    elif check_arg('-o'):
-      options.output_file = consume_arg()
     elif arg.startswith('-o'):
       options.output_file = removeprefix(arg, '-o')
-      newargs[i] = ''
     elif check_arg('-target') or check_arg('--target'):
       options.target = consume_arg()
       if options.target not in ('wasm32', 'wasm64', 'wasm64-unknown-emscripten', 'wasm32-unknown-emscripten'):
@@ -1502,6 +1493,12 @@ def consume_arg_file():
       options.dash_M = True
     elif arg == '-fsyntax-only':
       options.syntax_only = True
+    elif arg in SIMD_INTEL_FEATURE_TOWER or arg in SIMD_NEON_FLAGS:
+      # SSEx is implemented on top of SIMD128 instruction set, but do not pass SSE flags to LLVM
+      # so it won't think about generating native x86 SSE code.
+      newargs[i] = ''
+    elif arg and (arg == '-' or not arg.startswith('-')):
+      options.input_files.append(arg)
 
   if should_exit:
     sys.exit(0)

test/test_other.py

@@ -12646,8 +12646,8 @@ def test_default_to_cxx(self):
     self.assertContained("'string' file not found", err)
 
     # But it works if we pass and explicit language mode.
-    self.run_process([EMCC, '-c', 'cxxfoo.h', '-x', 'c++-header'])
-    self.run_process([EMCC, '-c', 'cxxfoo.h', '-x', 'c++'])
+    self.run_process([EMCC, '-x', 'c++-header', '-c', 'cxxfoo.h'])
+    self.run_process([EMCC, '-x', 'c++', '-c', 'cxxfoo.h'])
 
   @parameterized({
     '': ([],),