[lld] [LLD] [COFF] Rewrite handling of the /debug: option. NFC. (PR #75175)

[Martin Storsjö via llvm-commits]

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@@ -1647,13 +1607,47 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   if (args.hasArg(OPT_force, OPT_force_multipleres))
     config->forceMultipleRes = true;
 
+  // Don't warn about long section names, such as .debug_info, for mingw (or
+  // when -debug:dwarf is requested, handled below).
+  if (config->mingw)
+    config->warnLongSectionNames = false;
+
+  bool doGC = true;
+
   // Handle /debug
-  DebugKind debug = parseDebugKind(args);
-  if (debug == DebugKind::Full || debug == DebugKind::Dwarf ||
-      debug == DebugKind::GHash || debug == DebugKind::NoGHash) {
-    config->debug = true;
-    config->incremental = true;
-    config->includeDwarfChunks = true;
+  bool shouldCreatePDB = false;
+  if (auto *arg = args.getLastArg(OPT_debug, OPT_debug_opt)) {
+    std::string s;
+    if (arg->getOption().getID() == OPT_debug)
+      s = "full";
+    else
+      s = StringRef(arg->getValue()).lower();
+    if (s == "fastlink") {
+      warn("/debug:fastlink unsupported; using /debug:full");
+      s = "full";
+    }
+    if (s == "none") {
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mstorsjo wrote:

But if there's no `/debug:` option at all, then we'd go with the initial value of `doGC` - which should be `true` for that case.

https://github.com/llvm/llvm-project/pull/75175