[clang] [clang] Introduce elementwise clz/ctz builtins (PR #131995)

[Fraser Cormack via cfe-commits]

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@@ -1484,6 +1484,18 @@ def ElementwiseSubSat : Builtin {
   let Prototype = "void(...)";
 }
 
+def ElementwiseClz : Builtin {
+  let Spellings = ["__builtin_elementwise_clz"];
+  let Attributes = [NoThrow, Const, CustomTypeChecking, Constexpr];
+  let Prototype = "void(...)";
+}
+
+def ElementwiseCtz : Builtin {
+  let Spellings = ["__builtin_elementwise_ctz"];
+  let Attributes = [NoThrow, Const, CustomTypeChecking, Constexpr];
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frasercrmck wrote:

Ah no, the documentation says that the integer builtins may be called in a constexpr context, so `Constexpr` is correct and the patch needs to account for that. Will update.

https://github.com/llvm/llvm-project/pull/131995