Update documentation and few more defines

docs/source/getting_started/installation.rst

@@ -87,7 +87,7 @@ not regularly tested:
 Build prerequisites
 ^^^^^^^^^^^^^^^^^^^
 
-A C++ compiler with C++17 support is required as well as some standard tools
+A C++ compiler with C++20 support is required as well as some standard tools
 such as GNU Flex, GNU Bison (>=3.8), Make, and Python (>=3.11). Some additional
 tools: readline, libffi, Tcl and zlib; are optional but enabled by default (see
 :makevar:`ENABLE_*` settings in Makefile). Graphviz and Xdot are used by the

docs/source/yosys_internals/extending_yosys/contributing.rst

@@ -286,7 +286,7 @@ have incorrect results in unusual situations.
 Coding style
 ~~~~~~~~~~~~
 
-Yosys is written in C++17.
+Yosys is written in C++20.
 
 In general Yosys uses ``int`` instead of ``size_t``. To avoid compiler warnings
 for implicit type casts, always use ``GetSize(foobar)`` instead of

docs/source/yosys_internals/index.rst

@@ -25,7 +25,7 @@ wide range of real-world designs, including the `OpenRISC 1200 CPU`_, the
 
 .. _k68 CPU: http://opencores.org/projects/k68
 
-Yosys is written in C++, targeting C++17 at minimum. This chapter describes some
+Yosys is written in C++, targeting C++20 at minimum. This chapter describes some
 of the fundamental Yosys data structures. For the sake of simplicity the C++
 type names used in the Yosys implementation are used in this chapter, even
 though the chapter only explains the conceptual idea behind it and can be used

kernel/yosys_common.h

@@ -120,10 +120,10 @@
 #  define YS_MAYBE_UNUSED
 #endif
 
-#if __cplusplus >= 201703L
+#if __cplusplus >= 202002L
 #  define YS_FALLTHROUGH [[fallthrough]];
 #else
-#  error "C++17 or later compatible compiler is required"
+#  error "C++20 or later compatible compiler is required"
 #endif
 
 #if defined(__has_cpp_attribute) && __has_cpp_attribute(gnu::cold)

pyosys/generator.py

@@ -376,7 +376,7 @@ class PyosysWrapperGenerator(object):
     def make_preprocessor_options(self):
         py_include = get_paths()["include"]
         preprocessor_bin = shutil.which("clang++") or "g++"
-        cxx_std = os.getenv("CXX_STD", "c++17")
+        cxx_std = os.getenv("CXX_STD", "c++20")
         return ParserOptions(
             preprocessor=make_gcc_preprocessor(
                 defines=["_YOSYS_", "YOSYS_ENABLE_PYTHON"],

tests/functional/test_functional.py

@@ -21,7 +21,7 @@ def yosys(script):
     run([base_path / 'yosys', '-Q', '-p', script])
 
 def compile_cpp(in_path, out_path, args):
-    run(['g++', '-g', '-std=c++17'] + args + [str(in_path), '-o', str(out_path)])
+    run(['g++', '-g', '-std=c++20'] + args + [str(in_path), '-o', str(out_path)])
 
 def yosys_synth(verilog_file, rtlil_file):
     yosys(f"read_verilog {quote(verilog_file)} ; prep ; setundef -undriven -undef ; write_rtlil {quote(rtlil_file)}")