[arith] Allow integer casts of 0-D vectors

[bkramer]

Summary

This just works, no reason to disallow it.

mlir/include/mlir/Dialect/Arith/IR/ArithOps.td

class Arith_CastOp<string mnemonic, TypeConstraint From, TypeConstraint To,
     Results<(outs To:$out)> {
   let assemblyFormat = "$in attr-dict `:` type($in) `to` type($out)";
 }
 
 // Casts do not accept indices. Type constraint for signless-integer-like types
 // excluding indices: signless integers, vectors or tensors thereof.
 def SignlessFixedWidthIntegerLike : TypeConstraint<Or<[
         AnySignlessInteger.predicate,
-        VectorOf<[AnySignlessInteger]>.predicate,
+        VectorOfAnyRankOf<[AnySignlessInteger]>.predicate,
         TensorOf<[AnySignlessInteger]>.predicate]>,
     "signless-fixed-width-integer-like">;
 
 // Cast from an integer type to another integer type.
 class Arith_IToICastOp<string mnemonic, list<Trait> traits = []> :
     Arith_CastOp<mnemonic, SignlessFixedWidthIntegerLike,
                            SignlessFixedWidthIntegerLike,
                            traits #

mlir/test/Conversion/ArithToLLVM/arith-to-llvm.mlir

// CHECK-NEXT: = llvm.sext %arg0 : i3 to i6
   %0 = arith.extsi %arg0 : i3 to i6
 // CHECK-NEXT: = llvm.zext %arg0 : i3 to i6
   %1 = arith.extui %arg0 : i3 to i6
 // CHECK-NEXT: = llvm.trunc %arg0 : i3 to i2
    %2 = arith.trunci %arg0 : i3 to i2
   return
 }
 
+// CHECK-LABEL: @integer_cast_0d_vector
+func.func @integer_cast_0d_vector(%arg0 : vector<i3>) {
+// CHECK: %[[ARG0:.*]] = builtin.unrealized_conversion_cast
+// CHECK-NEXT: = llvm.sext %[[ARG0]] : vector<1xi3> to vector<1xi6>
+  %0 = arith.extsi %arg0 : vector<i3> to vector<i6>
+// CHECK-NEXT: = llvm.zext %[[ARG0]] : vector<1xi3> to vector<1xi6>
+  %1 = arith.extui %arg0 : vector<i3> to vector<i6>
+// CHECK-NEXT: = llvm.trunc %[[ARG0]] : vector<1xi3> to vector<1xi2>
+  %2 = arith.trunci %arg0 : vector<i3> to vector<i2>
+  return
+}
+
 // CHECK-LABEL: func @fcmp(%arg0: f32, %arg1: f32) {
 func.func @fcmp(f32, f32) -> () {
 ^bb0(%arg0: f32, %arg1: f32):
   // CHECK:      llvm.fcmp "oeq" %arg0, %arg1 : f32
   // CHECK-NEXT: llvm.fcmp "ogt" %arg0, %arg1 : f32
   // CHECK-NEXT: llvm.fcmp "oge" %arg0, %arg1 : f32
   // CHECK-NEXT: llvm.fcmp "olt" %arg0, %arg1 : f32
   // CHECK-NEXT: llvm.fcmp "ole" %arg0, %arg1 : f32