[clang] [clang] Add support for MSVC force inline attrs (PR #185282)

[Trung Nguyen via cfe-commits]

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@@ -5181,6 +5181,18 @@ OptimizeNoneAttr *Sema::mergeOptimizeNoneAttr(Decl *D,
 }
 
 static void handleAlwaysInlineAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  AlwaysInlineAttr AIA(S.Context, AL);
+  if (!S.getLangOpts().MicrosoftExt &&
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trungnt2910 wrote:

> That's expected behavior -- we diagnose when attributes are ignored. You get the same behavior with other attributes: https://godbolt.org/z/sGn87r3o6

`[[msvc::constexpr]]` is a weird semi-undocumented attribute - it is not specified on the official Microsoft Docs and only explained on the [Visual Studio Feedback](https://developercommunity.visualstudio.com/t/10259132#T-N10259447) page when a LLVM contributor specifically asked them about it.

Many other less esoteric `[[msvc::` attributes are left unguarded, such as the opposite of the newly added attributes, `[[msvc::noinline]]`: https://godbolt.org/z/W8519n6d1



https://github.com/llvm/llvm-project/pull/185282