[clang] [AArch64]: Refactor target parser to use Bitset. (PR #65423)

[via cfe-commits]

================
@@ -18,38 +18,39 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include <optional>
+#include <sstream>
 #include <string>
 
 using namespace llvm;
 
 namespace {
 const char *ARMArch[] = {
-    "armv4",        "armv4t",      "armv5",          "armv5t",      "armv5e",
-    "armv5te",      "armv5tej",    "armv6",          "armv6j",      "armv6k",
-    "armv6hl",      "armv6t2",     "armv6kz",        "armv6z",      "armv6zk",
-    "armv6-m",      "armv6m",      "armv6sm",        "armv6s-m",    "armv7-a",
-    "armv7",        "armv7a",      "armv7ve",        "armv7hl",     "armv7l",
-    "armv7-r",      "armv7r",      "armv7-m",        "armv7m",      "armv7k",
-    "armv7s",       "armv7e-m",    "armv7em",        "armv8-a",     "armv8",
-    "armv8a",       "armv8l",      "armv8.1-a",      "armv8.1a",    "armv8.2-a",
-    "armv8.2a",     "armv8.3-a",   "armv8.3a",       "armv8.4-a",   "armv8.4a",
-    "armv8.5-a",    "armv8.5a",    "armv8.6-a",      "armv8.6a",    "armv8.7-a",
-    "armv8.7a",     "armv8.8-a",   "armv8.8a",       "armv8.9-a",   "armv8.9a",
-    "armv8-r",      "armv8r",      "armv8-m.base",   "armv8m.base", "armv8-m.main",
-    "armv8m.main",  "iwmmxt",      "iwmmxt2",        "xscale",      "armv8.1-m.main",
-    "armv9-a",      "armv9",       "armv9a",         "armv9.1-a",   "armv9.1a",
-    "armv9.2-a",    "armv9.2a",    "armv9.3-a",      "armv9.3a",    "armv9.4-a",
+    "armv4",       "armv4t",    "armv5",        "armv5t",      "armv5e",
+    "armv5te",     "armv5tej",  "armv6",        "armv6j",      "armv6k",
+    "armv6hl",     "armv6t2",   "armv6kz",      "armv6z",      "armv6zk",
+    "armv6-m",     "armv6m",    "armv6sm",      "armv6s-m",    "armv7-a",
+    "armv7",       "armv7a",    "armv7ve",      "armv7hl",     "armv7l",
+    "armv7-r",     "armv7r",    "armv7-m",      "armv7m",      "armv7k",
+    "armv7s",      "armv7e-m",  "armv7em",      "armv8-a",     "armv8",
+    "armv8a",      "armv8l",    "armv8.1-a",    "armv8.1a",    "armv8.2-a",
+    "armv8.2a",    "armv8.3-a", "armv8.3a",     "armv8.4-a",   "armv8.4a",
+    "armv8.5-a",   "armv8.5a",  "armv8.6-a",    "armv8.6a",    "armv8.7-a",
+    "armv8.7a",    "armv8.8-a", "armv8.8a",     "armv8.9-a",   "armv8.9a",
+    "armv8-r",     "armv8r",    "armv8-m.base", "armv8m.base", "armv8-m.main",
+    "armv8m.main", "iwmmxt",    "iwmmxt2",      "xscale",      "armv8.1-m.main",
+    "armv9-a",     "armv9",     "armv9a",       "armv9.1-a",   "armv9.1a",
+    "armv9.2-a",   "armv9.2a",  "armv9.3-a",    "armv9.3a",    "armv9.4-a",
     "armv9.4a",
 };
 
-template <ARM::ISAKind ISAKind>
-std::string FormatExtensionFlags(uint64_t Flags) {
+template <ARM::ISAKind ISAKind, typename T>
+std::string FormatExtensionFlags(T Flags) {
   std::vector<StringRef> Features;
 
-  if (ISAKind == ARM::ISAKind::AARCH64) {
+  if constexpr (ISAKind == ARM::ISAKind::AARCH64) {
     // AEK_NONE is not meant to be shown to the user so the target parser
     // does not recognise it. It is relevant here though.
-    if (Flags & AArch64::AEK_NONE)
+    if (Flags.test(AArch64::AEK_NONE))
----------------
sdesmalen-arm wrote:

This assumes that `T` has a `test()` method, which is only true for the AArch64 ISAKind branch, which requires you to use the `constexpr` if-condition so that the compiler must fold away the other branch.

Can you write this in such a way that you don't need to make that assumption and don't need the constexpr? e.g. by having an overloaded `FormatExtensionFlags`, one for `uint64_t` and one for `Bitset`.

https://github.com/llvm/llvm-project/pull/65423