[clang] [clang] constexpr built-in elementwise add_sat function. (PR #119082)

[via cfe-commits]

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@@ -11339,6 +11339,31 @@ bool VectorExprEvaluator::VisitCallExpr(const CallExpr *E) {
 
     return Success(APValue(ResultElements.data(), ResultElements.size()), E);
   }
+  case Builtin::BI__builtin_elementwise_add_sat: {
+    APValue SourceLHS, SourceRHS;
+    if (!EvaluateAsRValue(Info, E->getArg(0), SourceLHS) ||
+        !EvaluateAsRValue(Info, E->getArg(1), SourceRHS))
+      return false;
+
+    QualType DestEltTy = E->getType()->castAs<VectorType>()->getElementType();
+    unsigned SourceLen = SourceLHS.getVectorLength();
+    SmallVector<APValue, 4> ResultElements;
+    ResultElements.reserve(SourceLen);
+
+    for (unsigned EltNum = 0; EltNum < SourceLen; ++EltNum) {
+      APSInt LHS = SourceLHS.getVectorElt(EltNum).getInt();
+      APSInt RHS = SourceRHS.getVectorElt(EltNum).getInt();
+      switch (E->getBuiltinCallee()) {
+      case Builtin::BI__builtin_elementwise_add_sat:
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cor3ntin wrote:

Can that be anything else here? Shouldn't we just assert or remove the test entirely? 

https://github.com/llvm/llvm-project/pull/119082