[MLIR] Remove empty shape operands from `cstr_broadcastable` ops

mlir/lib/Dialect/Shape/IR/Shape.cpp

 //===----------------------------------------------------------------------===//
 
 void CstrBroadcastableOp::getCanonicalizationPatterns(
     RewritePatternSet &patterns, MLIRContext *context) {
   // Canonicalization patterns have overlap with the considerations during
   // folding in case additional shape information is inferred at some point that
   // does not result in folding.
   patterns.add<CstrBroadcastableEqOps,
-               RemoveDuplicateOperandsPattern<CstrBroadcastableOp>>(context);
+               RemoveDuplicateOperandsPattern<CstrBroadcastableOp>,
+               RemoveEmptyShapeOperandsPattern<CstrBroadcastableOp>>(context);
 }
 
 // Return true if there is exactly one attribute not representing a scalar
 // broadcast.
 static bool hasAtMostSingleNonScalar(ArrayRef<Attribute> attributes) {
   bool nonScalarSeen = false;
   for (Attribute a : attributes) {
     if (!a || a.cast<DenseIntElementsAttr>().getNumElements() != 0) {

mlir/test/Dialect/Shape/canonicalize.mlir

func @f() {
   %cs0 = shape.const_shape [3, 1] : !shape.shape
   %cs1 = shape.const_shape [1, 5] : !shape.shape
   %0 = shape.cstr_broadcastable %cs0, %cs1 : !shape.shape, !shape.shape
   "consume.witness"(%0) : (!shape.witness) -> ()
   return
 }
 
 // -----
+// Empty shape arguments can be removed from broadcastable ops.
+// CHECK-LABEL: func @f
+// CHECK-SAME:  (%[[ARG0:.*]]: tensor<?xindex>, %[[ARG1:.*]]: tensor<?xindex>)
+func @f(%arg0 : tensor<?xindex>, %arg1 : tensor<?xindex>) {
+  // CHECK-NOT: const_shape
+  // CHECK: cstr_broadcastable %[[ARG0]], %[[ARG1]] : tensor<?xindex>, tensor<?xindex>
+  %0 = shape.const_shape [] : !shape.shape
+  %1 = shape.cstr_broadcastable %arg0, %arg1, %0
+      : tensor<?xindex>, tensor<?xindex>, !shape.shape
+  "consume.witness"(%1) : (!shape.witness) -> ()
+  return
+}
+
+// -----
 // Broadcastable with non-broadcastable constant shapes is always false
 // CHECK-LABEL: func @static_non_broadcastable
 func @static_non_broadcastable() {
   // CHECK-NEXT: shape.const_shape
   // CHECK-NEXT: shape.const_shape
   // CHECK-NEXT: shape.cstr_broadcastable
   // CHECK-NEXT: consume.witness
   // CHECK-NEXT: return