[clang] [Driver][BoundsSafety] Add -fexperimental-bounds-safety flag (PR #70480)

[Dan Liew via cfe-commits]

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@@ -3618,6 +3618,27 @@ void CompilerInvocationBase::GenerateLangArgs(const LangOptions &Opts,
     GenerateArg(Consumer, OPT_frandomize_layout_seed_EQ, Opts.RandstructSeed);
 }
 
+static void CheckBoundsSafetyLang(InputKind IK, DiagnosticsEngine &Diags) {
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delcypher wrote:

There are various different options here.

1. The frontend silently accepts`-fexperimental-bounds-safety` with `-x c++` but doesn't actually enable `fexperimental-bounds-safety`.
2. The frontend accepts`-fexperimental-bounds-safety` with `-x c++` enables `-fexperimental-bounds-safety` and probably crashes because it's not supported.
3. The frontend rejects`-fexperimental-bounds-safety` with `-x c++` with an error.

I don't like (1.) because when writing frontend only tests it is inviting someone to accidentally write a test incorrectly because the frontend would never complain about the invalid configuration.

I don't like (2.) because crashing really isn't good when it could so easily be prevented.

I think we should do (3.) because it has none of the previously mentioned downsides.



https://github.com/llvm/llvm-project/pull/70480