[clang] [Headers][X86] VectorExprEvaluator::VisitCallExpr / InterpretBuiltin - allow PALIGNR byte shift intrinsics to be used in constexpr (PR #162005)

[Timm Baeder via cfe-commits]

================
@@ -2975,6 +2975,75 @@ static bool interp__builtin_vec_set(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+static bool interp__builtin_x86_psrldq_byteshift(InterpState &S, CodePtr OpPC,
+                                                 const CallExpr *Call,
+                                                 unsigned ID) {
+  assert(Call->getNumArgs() == 2);
+
+  APSInt ImmAPS = popToAPSInt(S, Call->getArg(1));
+  uint64_t Shift = ImmAPS.getZExtValue();
+
+  const Pointer &Concat = S.Stk.pop<Pointer>();
+  if (!Concat.getFieldDesc()->isPrimitiveArray())
+    return false;
+
+  unsigned NumElems = Concat.getNumElems();
+  const Pointer &Dst = S.Stk.peek<Pointer>();
+  PrimType ElemPT = Concat.getFieldDesc()->getPrimType();
+
+  TYPE_SWITCH(ElemPT, {
+    for (unsigned I = 0; I < NumElems; ++I) {
+      if (I + Shift < NumElems)
+        Dst.elem<T>(I) = Concat.elem<T>(I + Shift);
+      else
+        Dst.elem<T>(I) = T();
+    }
+  });
+
+  Dst.initializeAllElements();
+
+  return true;
+}
+
+static bool interp__builtin_x86_palignr(InterpState &S, CodePtr OpPC,
+                                        const CallExpr *Call, unsigned ID) {
+  assert(Call->getNumArgs() == 3);
+
+  APSInt ImmAPS = popToAPSInt(S, Call->getArg(2));
+  uint64_t Shift = ImmAPS.getZExtValue();
+
+  const Pointer &VecB = S.Stk.pop<Pointer>();
+  if (!VecB.getFieldDesc()->isPrimitiveArray())
+    return false;
+
+  const Pointer &VecA = S.Stk.pop<Pointer>();
+  if (!VecA.getFieldDesc()->isPrimitiveArray())
+    return false;
+
+  const Pointer &Dst = S.Stk.peek<Pointer>();
+  PrimType ElemPT = VecA.getFieldDesc()->getPrimType();
----------------
tbaederr wrote:

```suggestion
  PrimType ElemT = VecA.getFieldDesc()->getPrimType();
```

https://github.com/llvm/llvm-project/pull/162005