[llvm] [Support] Accept -no-<name> to negate cl::opt<bool> (PR #224978)

[James Henderson via llvm-commits]

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@@ -551,7 +551,17 @@ Option *CommandLineParser::LookupOption(SubCommand &Sub, StringRef &Arg,
   // If we have an equals sign, remember the value.
   if (EqualPos == StringRef::npos) {
     // Look up the option.
-    return Sub.OptionsMap.lookup(Arg);
+    if (Option *O = Sub.OptionsMap.lookup(Arg))
+      return O;
+    // -no-<name> negates the boolean option <name>.
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jh7370 wrote:

I assume this additional logic here isn't going to significantly degrade the cost of command-line parsing? I imagine some tools have many options passed to them, so it wouldn't take much for the cost of running that tool to increase in a noticeable way.

https://github.com/llvm/llvm-project/pull/224978