[llvm] Use lit internal shell by default

This should result in a 10-15% test time improvement and also richer
test failure outputn on Linux where it is not yet the default. We can do
this now that all of the tests have been ported over to work with lit's
internal shell.

Fixes #102697.

Reviewers: ilovepi, petrhosek

Reviewed By: ilovepi, petrhosek

Pull Request: llvm/llvm-project#157237

Author: boomanaiden154

llvm/test/lit.cfg.py

@@ -17,6 +17,17 @@
 # name: The name of this test suite.
 config.name = "LLVM"
 
+# TODO: Consolidate the logic for turning on the internal shell by default for all LLVM test suites.
+# See https://github.com/llvm/llvm-project/issues/106636 for more details.
+#
+# We prefer the lit internal shell which provides a better user experience on failures
+# and is faster unless the user explicitly disables it with LIT_USE_INTERNAL_SHELL=0
+# env var.
+use_lit_shell = True
+lit_shell_env = os.environ.get("LIT_USE_INTERNAL_SHELL")
+if lit_shell_env:
+    use_lit_shell = lit.util.pythonize_bool(lit_shell_env)
+
 # testFormat: The test format to use to interpret tests.
 extra_substitutions = extra_substitutions = (
     [
@@ -26,9 +37,7 @@
     if config.enable_profcheck
     else []
 )
-config.test_format = lit.formats.ShTest(
-    not llvm_config.use_lit_shell, extra_substitutions
-)
+config.test_format = lit.formats.ShTest(not use_lit_shell, extra_substitutions)
 
 # suffixes: A list of file extensions to treat as test files. This is overriden
 # by individual lit.local.cfg files in the test subdirectories.