[clang] First draft: [Clang] Add constant evaluation support for x86 psadbw/p… (PR #169253)

[Simon Pilgrim via cfe-commits]

================
@@ -12078,6 +12080,54 @@ static bool evalPackBuiltin(const CallExpr *E, EvalInfo &Info, APValue &Result,
   return true;
 }
 
+static bool EvaluatePSADBW128(const CallExpr *E, EvalInfo &Info, APValue &Result) {
+  // 1) Evaluate the arguments into APValues
+  APValue A, B;
+  if (!Evaluate(A, Info, E->getArg(0)) ||
+      !Evaluate(B, Info, E->getArg(1)))
+    return false;
+
+  if (!A.isVector() || !B.isVector())
----------------
RKSimon wrote:

The ia32_psadbw builtins have fixed types - don't bother with so much isVector/getVectorLength checks - `assert((getVectorLength() % 16) == 0)` should be enough.

https://github.com/llvm/llvm-project/pull/169253