[clang] [Wunsafe-buffer-usage] Address some false positives in handling array indices that are decidably correct (PR #117370)

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@@ -439,8 +439,16 @@ AST_MATCHER(ArraySubscriptExpr, isSafeArraySubscript) {
       dyn_cast<StringLiteral>(Node.getBase()->IgnoreParenImpCasts());
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mxms0 wrote:

I think ultimately going to the Sema code is probably the better place to be, but I'm not sure who's working on that or if they have any urgency to land it. Ergo I'm in favor of landing this and working with the original owner to find the desired end state, as long as you all think that's an acceptable medium state. :)

https://github.com/llvm/llvm-project/pull/117370