[X86][Costmodel] `getReplicationShuffleCost()`: promote 1 bit-wide elements to 16 bit when have AVX512BW

Here we get pretty lucky. AVX512F does not provide any instructions
to convert between a `k` vector mask and a vector,
but AVX512BW adds `{k}<->nX{i8,i16}`conversions,
and just as it happens, with AVX512BW we have a i16 shuffle.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D113915

llvm/lib/Target/X86/X86TargetTransformInfo.cpp

@@ -3664,6 +3664,13 @@ X86TTIImpl::getReplicationShuffleCost(Type *EltTy, int ReplicationFactor,
     if (!ST->hasVBMI())
       PromEltTyBits = 32; // promote to i32, AVX512F.
     break;                // AVX512VBMI
+  case 1:
+    // There is no support for shuffling i1 elements. We *must* promote.
+    if (ST->hasBWI()) {
+      PromEltTyBits = 16; // promote to i16, AVX512BW.
+      break;
+    }
+    return bailout();
   default:
     return bailout();
   }