[clang] [clang] constexpr built-in reduce add function. (PR #116243)

[Simon Pilgrim via cfe-commits]

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@@ -13528,6 +13528,20 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
     return Success(DidOverflow, E);
   }
 
+  case Builtin::BI__builtin_reduce_add: {
+    APValue Source;
+    if (!EvaluateAsRValue(Info, E->getArg(0), Source))
+      return false;
+
+    auto SourceLen = Source.getVectorLength();
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RKSimon wrote:

(style) Avoid auto

https://github.com/llvm/llvm-project/pull/116243