[clang] [Clang]Throw frontend error for target feature mismatch when using `flatten` attribute (PR #150044)

[Abhishek Kaushik via cfe-commits]

================
@@ -5232,9 +5232,11 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
     // since otherwise we could be making a conditional call after a check for
     // the proper cpu features (and it won't cause code generation issues due to
     // function based code generation).
-    if (TargetDecl->hasAttr<AlwaysInlineAttr>() &&
-        (TargetDecl->hasAttr<TargetAttr>() ||
-         (CurFuncDecl && CurFuncDecl->hasAttr<TargetAttr>())))
+    if ((TargetDecl->hasAttr<AlwaysInlineAttr>() &&
+         (TargetDecl->hasAttr<TargetAttr>() ||
+          (CurFuncDecl && CurFuncDecl->hasAttr<TargetAttr>()))) ||
+        (CurFuncDecl && CurFuncDecl->hasAttr<FlattenAttr>() &&
+         TargetDecl->hasAttr<TargetAttr>()))
----------------
abhishek-kaushik22 wrote:

>From what I understand, we only need to check that the callee function has `TargetAttr` because the error is inlining a function that uses a target feature which the caller isn't compiled for. The caller having `TargetAttr` isn't required to reproduce the crash.

https://github.com/llvm/llvm-project/pull/150044