[clang] [X86][Clang] VectorExprEvaluator::VisitCallExpr / InterpretBuiltin - allow AVX512 mask predicate intrinsics to be used in constexpr (PR #173739)

[Timm Baeder via cfe-commits]

================
@@ -3421,6 +3421,30 @@ static bool interp__builtin_ia32_cvt_vec2mask(InterpState &S, CodePtr OpPC,
   pushInteger(S, RetMask, Call->getType());
   return true;
 }
+
+static bool interp__builtin_ia32_cvt_mask2vec(InterpState &S, CodePtr OpPC,
+                                              const CallExpr *Call,
+                                              unsigned ID) {
+  assert(Call->getNumArgs() == 1);
+
+  APSInt Mask = popToAPSInt(S, Call->getArg(0));
+
+  const Pointer &Vec = S.Stk.peek<Pointer>();
+  unsigned NumElems = Vec.getNumElems();
+  PrimType ElemT = Vec.getFieldDesc()->getPrimType();
+
+  for (unsigned i = 0; i < NumElems; ++i) {
----------------
tbaederr wrote:

```suggestion
  for (unsigned I = 0; i != NumElems; ++i) {
```

https://github.com/llvm/llvm-project/pull/173739