gcc-plugins: Remove cyc_complexity

This plugin has no impact on the resulting binary, is disabled
under COMPILE_TEST, and is not enabled on any builds I'm aware of.
Additionally, given the clarified purpose of GCC plugins in the kernel,
remove cyc_complexity.

Cc: Masahiro Yamada <[e-mail]>
Cc: Michal Marek <[e-mail]>
Cc: Nick Desaulniers <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Kees Cook <[e-mail]>
Reviewed-by: Miguel Ojeda <[e-mail]>
Reviewed-by: Nathan Chancellor <[e-mail]>
Acked-by: Nick Desaulniers <[e-mail]>
Acked-by: Ard Biesheuvel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/kbuild/gcc-plugins.rst

···
 in the kernel config::
 
 	CONFIG_GCC_PLUGINS=y
-	CONFIG_GCC_PLUGIN_CYC_COMPLEXITY=y
 	CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y
 	...
 
···
 right under scripts/gcc-plugins/. Creating subdirectories is not supported.
 It must be added to scripts/gcc-plugins/Makefile, scripts/Makefile.gcc-plugins
 and a relevant Kconfig file.
-See the cyc_complexity_plugin.c (CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) GCC plugin.

scripts/Makefile.gcc-plugins

···
 # SPDX-License-Identifier: GPL-2.0
 
-gcc-plugin-$(CONFIG_GCC_PLUGIN_CYC_COMPLEXITY)	+= cyc_complexity_plugin.so
-
 gcc-plugin-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)	+= latent_entropy_plugin.so
 gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)		\
 		+= -DLATENT_ENTROPY_PLUGIN

scripts/gcc-plugins/Kconfig

···
 
 if GCC_PLUGINS
 
-config GCC_PLUGIN_CYC_COMPLEXITY
-	bool "Compute the cyclomatic complexity of a function" if EXPERT
-	depends on !COMPILE_TEST	# too noisy
-	help
-	  The complexity M of a function's control flow graph is defined as:
-	   M = E - N + 2P
-	  where
-
-	  E = the number of edges
-	  N = the number of nodes
-	  P = the number of connected components (exit nodes).
-
-	  Enabling this plugin reports the complexity to stderr during the
-	  build. It mainly serves as a simple example of how to create a
-	  gcc plugin for the kernel.
-
 config GCC_PLUGIN_SANCOV
 	bool
 	# Plugin can be removed once the kernel only supports GCC 6+

scripts/gcc-plugins/cyc_complexity_plugin.c

···
-/*
- * Copyright 2011-2016 by Emese Revfy <[e-mail]>
- * Licensed under the GPL v2, or (at your option) v3
- *
- * Homepage:
- * https://github.com/ephox-gcc-plugins/cyclomatic_complexity
- *
- * https://en.wikipedia.org/wiki/Cyclomatic_complexity
- * The complexity M is then defined as:
- * M = E - N + 2P
- * where
- *
- *  E = the number of edges of the graph
- *  N = the number of nodes of the graph
- *  P = the number of connected components (exit nodes).
- *
- * Usage (4.5 - 5):
- * $ make clean; make run
- */
-
-#include "gcc-common.h"
-
-__visible int plugin_is_GPL_compatible;
-
-static struct plugin_info cyc_complexity_plugin_info = {
-	.version	= "20160225",
-	.help		= "Cyclomatic Complexity\n",
-};
-
-static unsigned int cyc_complexity_execute(void)
-{
-	int complexity;
-	expanded_location xloc;
-
-	/* M = E - N + 2P */
-	complexity = n_edges_for_fn(cfun) - n_basic_blocks_for_fn(cfun) + 2;
-
-	xloc = expand_location(DECL_SOURCE_LOCATION(current_function_decl));
-	fprintf(stderr, "Cyclomatic Complexity %d %s:%s\n", complexity,
-		xloc.file, DECL_NAME_POINTER(current_function_decl));
-
-	return 0;
-}
-
-#define PASS_NAME cyc_complexity
-
-#define NO_GATE
-#define TODO_FLAGS_FINISH TODO_dump_func
-
-#include "gcc-generate-gimple-pass.h"
-
-__visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version)
-{
-	const char * const plugin_name = plugin_info->base_name;
-
-	PASS_INFO(cyc_complexity, "ssa", 1, PASS_POS_INSERT_AFTER);
-
-	if (!plugin_default_version_check(version, &gcc_version)) {
-		error(G_("incompatible gcc/plugin versions"));
-		return 1;
-	}
-
-	register_callback(plugin_name, PLUGIN_INFO, NULL,
-				&cyc_complexity_plugin_info);
-	register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
-				&cyc_complexity_pass_info);
-
-	return 0;
-}