Speed up emcc -v by not running sanity checks.

ince some build tools run `emcc -v` regularly we want to be fast.  This
change avoid running sanity checks which means fewer subprocesses.

On my machine this takes `emcc -v ` from ~300 ro ~200 ms.

Sanity checks are still run on first use.

See: #13004

Author: sbc100

ChangeLog.md

@@ -23,6 +23,11 @@ Current Trunk
 
 2.0.11: 12/17/2020
 ------------------
+- `emcc -v` no longer forces the running the sanity checks.  Sanity checks
+  are always run on first use (or when the cache is cleaned), and when
+  `EMCC_DEBUG` is set in the environment.  Not forcing this allows `emcc -v`
+  to run a little faster which speeds up build systems that depend on running
+  this frequently.
 - An upstream LLVM regression with global initializer linking has been fixed
   (#13038).
 - Remove a racy unneeded assertion about async dynamic linking (#13060).

docs/emcc.txt

@@ -401,10 +401,8 @@ Options that are modified or new in *emcc* are listed below:
 "-v"
    Turns on verbose output.
 
-   This will pass "-v" to *Clang*, and also enable "EMCC_DEBUG" to
-   generate intermediate files for the compiler's various stages. It
-   will also run Emscripten's internal sanity checks on the toolchain,
-   etc.
+   This will print the internal sub-commands run by emscripten as well
+   as "-v" to *Clang*.
 
    Tip:
 

emcc.py

@@ -796,9 +796,7 @@ def run(args):
   if len(args) == 1 and args[0] == '-v': # -v with no inputs
     # autoconf likes to see 'GNU' in the output to enable shared object support
     print('emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) %s' % shared.EMSCRIPTEN_VERSION, file=sys.stderr)
-    code = shared.check_call([clang, '-v'] + shared.get_clang_flags(), check=False).returncode
-    shared.check_sanity(force=True)
-    return code
+    return shared.check_call([clang, '-v'] + shared.get_clang_flags(), check=False).returncode
 
   if '-dumpmachine' in args:
     print(shared.get_llvm_target())
@@ -2519,7 +2517,6 @@ def consume_arg_file():
       options.ignore_dynamic_linking = True
     elif arg == '-v':
       shared.PRINT_STAGES = True
-      shared.check_sanity(force=True)
     elif check_arg('--shell-file'):
       options.shell_path = consume_arg_file()
     elif check_arg('--source-map-base'):

site/source/docs/getting_started/FAQ.rst

@@ -17,7 +17,7 @@ Why do I get multiple errors building basic code and the tests?
 
 All the tests in the :ref:`Emscripten test suite <emscripten-test-suite>` are known to build and pass on our test infrastructure, so if you see failures locally it is likely that there is some problem with your environment. (Rarely, there may be temporary breakage, but never on a tagged release version.)
 
-First call ``emcc -v``, which runs basic sanity checks and prints out useful environment information. If that doesn't help, follow the instructions in :ref:`verifying-the-emscripten-environment`.
+First call ``emcc -v``, prints out useful environment information. If that doesn't help, follow the instructions in :ref:`verifying-the-emscripten-environment`.
 
 You might also want to go through the :ref:`Tutorial` again, as it is updated as Emscripten changes.
 

site/source/docs/porting/Debugging.rst

@@ -57,7 +57,7 @@ directory (e.g. **/tmp** on UNIX).
 
 The debug logs can be analysed to profile and review the changes that were made in each step.
 
-.. note:: The debug mode can also be enabled by specifying the :ref:`verbose output <debugging-emcc-v>` compiler flag (``emcc -v``).
+.. note:: The more limited amount of debug information can also be enabled by specifying the :ref:`verbose output <debugging-emcc-v>` compiler flag (``emcc -v``).
 
 
 .. _debugging-compilation-settings:
@@ -121,10 +121,8 @@ Emscripten also supports some of Clang's sanitizers, such as :ref:`sanitizer_ubs
 emcc verbose output
 ===================
 
-Compiling with the :ref:`emcc -v <emcc-verbose>` option passes ``-v`` to LLVM and runs Emscripten's internal sanity checks on the toolchain.
-
-The verbose mode also enables Emscripten's :ref:`debugging-EMCC_DEBUG` to generate intermediate files for the compiler’s various stages.
-
+Compiling with the :ref:`emcc -v <emcc-verbose>` will cause Emscripten to output
+the sub-command that it runs as well as passes ``-v`` to Clang.
 
 .. _debugging-manual-debugging:
 

site/source/docs/tools_reference/emcc.rst

@@ -323,7 +323,8 @@ Options that are modified or new in *emcc* are listed below:
 ``-v``
   Turns on verbose output.
 
-  This will pass ``-v`` to *Clang*, and also enable ``EMCC_DEBUG`` to generate intermediate files for the compiler's various stages. It will also run Emscripten's internal sanity checks on the toolchain, etc.
+  This will print the internal sub-commands run by emscripten as well as ``-v``
+  to *Clang*.
 
   .. tip:: ``emcc -v`` is a useful tool for diagnosing errors. It works with or without other arguments.