RISC-V: Add new option -march=help to print all supported extensions

The output of -march=help is like below:

```
All available -march extensions for RISC-V:
        Name                Version
        i                       2.0, 2.1
        e                       2.0
        m                       2.0
        a                       2.0, 2.1
        f                       2.0, 2.2
        d                       2.0, 2.2
...
```

Also support -print-supported-extensions and --print-supported-extensions for
clang compatibility.

gcc/ChangeLog:

	PR target/109349

	* common/config/riscv/riscv-common.cc (riscv_arch_help): New.
	* config/riscv/riscv-protos.h (RISCV_MAJOR_VERSION_BASE): New.
	(RISCV_MINOR_VERSION_BASE): Ditto.
	(RISCV_REVISION_VERSION_BASE): Ditto.
	* config/riscv/riscv-c.cc (riscv_ext_version_value): Use enum
	rather than magic number.
	* config/riscv/riscv.h (riscv_arch_help): New.
	(EXTRA_SPEC_FUNCTIONS): Add riscv_arch_help.
	(DRIVER_SELF_SPECS): Handle -march=help, -print-supported-extensions and
	--print-supported-extensions.
	* config/riscv/riscv.opt (march=help): New.
	(print-supported-extensions): New.
	(-print-supported-extensions): New.
	* doc/invoke.texi (RISC-V Options): Document -march=help.

Reviewed-by: Christoph Müllner <christoph.muellner@vrull.eu>

gcc/common/config/riscv/riscv-common.cc

@@ -21,6 +21,8 @@ along with GCC; see the file COPYING3.  If not see
 #include <vector>
 
 #define INCLUDE_STRING
+#define INCLUDE_SET
+#define INCLUDE_MAP
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
@@ -2225,6 +2227,50 @@ riscv_get_valid_option_values (int option_code,
   return v;
 }
 
+const char *
+riscv_arch_help (int, const char **)
+{
+  /* Collect all exts, and sort it in canonical order.  */
+  struct extension_comparator {
+    bool operator()(const std::string& a, const std::string& b) const {
+      return subset_cmp(a, b) >= 1;
+    }
+  };
+  std::map<std::string, std::set<unsigned>, extension_comparator> all_exts;
+  for (const riscv_ext_version &ext : riscv_ext_version_table)
+    {
+      if (!ext.name)
+	break;
+      if (ext.name[0] == 'g')
+	continue;
+      unsigned version_value = (ext.major_version * RISCV_MAJOR_VERSION_BASE)
+				+ (ext.minor_version
+				   * RISCV_MINOR_VERSION_BASE);
+      all_exts[ext.name].insert(version_value);
+    }
+
+  printf("All available -march extensions for RISC-V:\n");
+  printf("\t%-20sVersion\n", "Name");
+  for (auto const &ext_info : all_exts)
+    {
+      printf("\t%-20s\t", ext_info.first.c_str());
+      bool first = true;
+      for (auto version : ext_info.second)
+	{
+	  if (first)
+	    first = false;
+	  else
+	    printf(", ");
+	  unsigned major = version / RISCV_MAJOR_VERSION_BASE;
+	  unsigned minor = (version % RISCV_MAJOR_VERSION_BASE)
+			    / RISCV_MINOR_VERSION_BASE;
+	  printf("%u.%u", major, minor);
+	}
+      printf("\n");
+    }
+  exit (0);
+}
+
 /* Implement TARGET_OPTION_OPTIMIZATION_TABLE.  */
 static const struct default_options riscv_option_optimization_table[] =
   {

gcc/config/riscv/riscv-c.cc

@@ -37,7 +37,7 @@ along with GCC; see the file COPYING3.  If not see
 static int
 riscv_ext_version_value (unsigned major, unsigned minor)
 {
-  return (major * 1000000) + (minor * 1000);
+  return (major * RISCV_MAJOR_VERSION_BASE) + (minor * RISCV_MINOR_VERSION_BASE);
 }
 
 /* Implement TARGET_CPU_CPP_BUILTINS.  */

gcc/config/riscv/riscv-protos.h

@@ -780,4 +780,11 @@ const struct riscv_tune_info *
 riscv_parse_tune (const char *, bool);
 const cpu_vector_cost *get_vector_costs ();
 
+enum
+{
+  RISCV_MAJOR_VERSION_BASE = 1000000,
+  RISCV_MINOR_VERSION_BASE = 1000,
+  RISCV_REVISION_VERSION_BASE = 1,
+};
+
 #endif /* ! GCC_RISCV_PROTOS_H */

gcc/config/riscv/riscv.h

@@ -50,12 +50,14 @@ extern const char *riscv_expand_arch (int argc, const char **argv);
 extern const char *riscv_expand_arch_from_cpu (int argc, const char **argv);
 extern const char *riscv_default_mtune (int argc, const char **argv);
 extern const char *riscv_multi_lib_check (int argc, const char **argv);
+extern const char *riscv_arch_help (int argc, const char **argv);
 
 # define EXTRA_SPEC_FUNCTIONS						\
   { "riscv_expand_arch", riscv_expand_arch },				\
   { "riscv_expand_arch_from_cpu", riscv_expand_arch_from_cpu },		\
   { "riscv_default_mtune", riscv_default_mtune },			\
-  { "riscv_multi_lib_check", riscv_multi_lib_check },
+  { "riscv_multi_lib_check", riscv_multi_lib_check },			\
+  { "riscv_arch_help", riscv_arch_help },
 
 /* Support for a compile-time default CPU, et cetera.  The rules are:
    --with-arch is ignored if -march or -mcpu is specified.
@@ -109,6 +111,9 @@ ASM_MISA_SPEC
 
 #undef DRIVER_SELF_SPECS
 #define DRIVER_SELF_SPECS					\
+"%{march=help:%:riscv_arch_help()} "				\
+"%{print-supported-extensions:%:riscv_arch_help()} "		\
+"%{-print-supported-extensions:%:riscv_arch_help()} "		\
 "%{march=*:%:riscv_expand_arch(%*)} "				\
 "%{!march=*:%{mcpu=*:%:riscv_expand_arch_from_cpu(%*)}} "
 

gcc/config/riscv/riscv.opt

@@ -86,6 +86,18 @@ Target RejectNegative Joined Negative(march=)
 -march=	Generate code for given RISC-V ISA (e.g. RV64IM).  ISA strings must be
 lower-case.
 
+march=help
+Target RejectNegative
+-march=help	Print supported -march extensions.
+
+; -print-supported-extensions and --print-supported-extensions are added for
+; clang compatibility.
+print-supported-extensions
+Target Undocumented RejectNegative Alias(march=help)
+
+-print-supported-extensions
+Target Undocumented RejectNegative Alias(march=help)
+
 mtune=
 Target RejectNegative Joined Var(riscv_tune_string) Save
 -mtune=PROCESSOR	Optimize the output for PROCESSOR.

gcc/doc/invoke.texi

@@ -30207,7 +30207,8 @@ with @option{--with-isa-spec=} specifying a different default version.
 @item -march=@var{ISA-string}
 Generate code for given RISC-V ISA (e.g.@: @samp{rv64im}).  ISA strings must be
 lower-case.  Examples include @samp{rv64i}, @samp{rv32g}, @samp{rv32e}, and
-@samp{rv32imaf}.
+@samp{rv32imaf}. Additionally, a special value @option{help}
+(@option{-march=help}) is accepted to list all supported extensions.
 
 The syntax of the ISA string is defined as follows: