build: build with -O0 if Clang >= 16 is used

to workaround https://github.com/llvm/llvm-project/issues/62842,
per the test this issue only surfaces when compiling the tree
with
ae7bf2b80b
which is included in Clang version 16, and the issue disappears
when the tree is compiled with -O0.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes #14391

cmake/mode.common.cmake

@@ -39,3 +39,20 @@ check_cxx_compiler_flag(${_stack_usage_threshold_flag} _stack_usage_flag_support
 if(_stack_usage_flag_supported)
   string(APPEND CMAKE_CXX_FLAGS " ${_stack_usage_threshold_flag}")
 endif()
+
+if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND CMAKE_CXX_COMPILER_VERSION GREATER_EQUAL 16)
+  # workaround https://github.com/llvm/llvm-project/issues/62842
+  set(_original_level "${Seastar_OptimizationLevel_${build_mode}}")
+  set(_safe_level "0")
+  if(NOT _original_level STREQUAL _safe_level)
+    message(WARNING
+      "Changing optimization level from -O${_original_level} to -O${_safe_level} "
+      "due to https://github.com/llvm/llvm-project/issues/62842. "
+      "Please note -O0 is very slow that some tests might fail.")
+    string(REPLACE " -O${_original_level} " " -O${_safe_level} "
+      CMAKE_CXX_FLAGS_${build_mode}
+      "${CMAKE_CXX_FLAGS_${build_mode}}")
+  endif()
+  unset(_original_level)
+  unset(_safe_level)
+endif()

configure.py

@@ -18,6 +18,7 @@ import sys
 import tempfile
 import textwrap
 from distutils.spawn import find_executable
+from pkg_resources import parse_version
 
 curdir = os.getcwd()
 
@@ -163,6 +164,41 @@ def flag_supported(flag, compiler):
     return try_compile(flags=['-Werror'] + split, compiler=compiler)
 
 
+class OptimizationLevel:
+    warned = False
+
+    @classmethod
+    def _warn(cls, safe_level) -> None:
+        if cls.warned:
+            # only prints this warning for a single time
+            return
+        print('\033[91mWARN\033[00m: '
+              f'Changing optimization level to "-O{safe_level}" '
+              'due to https://github.com/llvm/llvm-project/issues/62842. '
+              'Please note -O0 is so slow that some tests might fail.')
+        cls.warned = True
+
+    def __call__(self, cxx_compiler, default_level):
+        # workaround https://github.com/llvm/llvm-project/issues/62842
+        if 'clang' not in cxx_compiler:
+            return default_level
+
+        proc = subprocess.run([cxx_compiler, '--version'],
+                              capture_output=True,
+                              check=True,
+                              text=True)
+        matched = re.match(r'clang version (\d+\.\d+.\d+)', proc.stdout)
+        if matched is None:
+            raise Exception(f'Unable to tell version of {cxx_compiler}')
+        if parse_version(matched.group(1)) < parse_version('16.0.0'):
+            return default_level
+        safe_level = '0'
+        if default_level == safe_level:
+            return default_level
+        self._warn(safe_level)
+        return safe_level
+optimization_level = OptimizationLevel()
+
 def linker_flags(compiler):
     src_main = 'int main(int argc, char **argv) { return 0; }'
     link_flags = ['-fuse-ld=lld']
@@ -1424,7 +1460,8 @@ for mode_level in args.mode_o_levels:
     modes[mode]['optimization-level'] = level
 
 for mode in modes:
-    modes[mode]['cxxflags'] += f' -O{modes[mode]["optimization-level"]}'
+    level = optimization_level(args.cxx, modes[mode]["optimization-level"])
+    modes[mode]['cxxflags'] += f' -O{level}'
 
 optimization_flags = [
     '--param inline-unit-growth=300', # gcc