[clang] [clang]Implement the c23 stdc bit builtins (PR #185978)

[Erich Keane via cfe-commits]

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@@ -2345,6 +2345,29 @@ static bool BuiltinPopcountg(Sema &S, CallExpr *TheCall) {
   return false;
 }
 
+/// Checks the __builtin_stdc_* builtins that take a single unsigned integer
+/// argument and return either int, bool, or the argument type.
+static bool BuiltinStdCBuiltin(Sema &S, CallExpr *TheCall,
+                               QualType ReturnType) {
+  if (S.checkArgCount(TheCall, 1))
+    return true;
+
+  ExprResult ArgRes = S.DefaultLvalueConversion(TheCall->getArg(0));
+  if (ArgRes.isInvalid())
+    return true;
+
+  Expr *Arg = ArgRes.get();
+  TheCall->setArg(0, Arg);
+
+  QualType ArgTy = Arg->getType();
+  if (!ArgTy->isUnsignedIntegerType())
+    return S.Diag(Arg->getBeginLoc(), diag::err_builtin_stdc_invalid_arg_type)
+           << 1 << ArgTy;
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erichkeane wrote:

This '1' needs a comment explaining what it is doing.

https://github.com/llvm/llvm-project/pull/185978