Make ReshapeOp return MHLO_AnyTensor instead of MHLO_StaticShapeTensor.

Note that this only removes the TableGen generated MLIR verification of the
return value. ReshapeOp::verify will still check the validity/compatiblity of
the input/output types.

PiperOrigin-RevId: 692274546

xla/mlir_hlo/mhlo/IR/hlo_ops.td

@@ -2842,7 +2842,7 @@ def MHLO_ReshapeOp: MHLO_Op<"reshape",
 
   let arguments = (ins MHLO_AnyTensor:$operand);
 
-  let results = (outs MHLO_StaticShapeTensor);
+  let results = (outs MHLO_AnyTensor);
   let hasFolder = 1;
   let hasCanonicalizer = 1;
   let hasVerifier = 1;

xla/mlir_hlo/mhlo/transforms/hlo_legalize_to_stablehlo/hlo_legalize_to_stablehlo.cc

@@ -59,6 +59,12 @@ bool hasPrivateFeaturesNotInStablehlo(HloOpTy hloOp) {
           mhlo::XlaRngGetAndUpdateStateOp>(hloOp.getOperation())) {
     return true;
   }
+  if (auto reshape = dyn_cast<mhlo::ReshapeOp>(hloOp.getOperation())) {
+    // Only mhlo and HLO support dynamic reshape results. stablehlo doesn't
+    // (yet), at the time of this writing.
+    auto t = dyn_cast<RankedTensorType>(reshape.getResult().getType());
+    if (t && !t.hasStaticShape()) return true;
+  }
   if constexpr (std::is_same<HloOpTy, mhlo::ConvolutionOp>::value) {
     // StableHLO convolution doesn't support "unknown" dimensions.
     // This is an esoteric feature of MHLO convolutions, and it's different

xla/mlir_hlo/tests/Dialect/mhlo/hlo-legalize-to-stablehlo.mlir

@@ -2143,6 +2143,15 @@ func.func @op_fusion(%arg0: tensor<f32>) -> tensor<f32> {
 
 // -----
 
+func.func @reshape_with_dynamic_size_convert(%arg0: tensor<?x1xi64, #mhlo.type_extensions<bounds = [7, ?]>>) -> tensor<?xi64, #mhlo.type_extensions<bounds = [7]>> {
+  // expected-error@+1 {{failed to legalize operation 'mhlo.reshape' that was explicitly marked illegal}}
+  %0 = "mhlo.reshape"(%arg0) : (tensor<?x1xi64, #mhlo.type_extensions<bounds = [7, ?]>>)
+       -> tensor<?xi64, #mhlo.type_extensions<bounds = [7]>>
+  return %0 : tensor<?xi64, #mhlo.type_extensions<bounds = [7]>>
+}
+
+// -----
+
 func.func @op_stochastic_convert(%arg0: tensor<f32>, %arg1: tensor<ui32>) -> tensor<i8> {
   // expected-error@+1 {{failed to legalize operation 'mhlo.stochastic_convert' that was explicitly marked illegal}}
   %0 = "mhlo.stochastic_convert"(%arg0, %arg1) : (tensor<f32>, tensor<ui32>) -> tensor<i8>

xla/mlir_hlo/tests/Dialect/mhlo/ops.mlir

@@ -2920,6 +2920,18 @@ func.func @reshape_invalid_shapes(%operand: tensor<2x4xf32>) -> tensor<3x3xf32>
 
 // -----
 
+// CHECK-LABEL: func @reshape_can_have_dynamic_dimensions
+func.func @reshape_can_have_dynamic_dimensions() -> tensor<?xi64, #mhlo.type_extensions<bounds = [7]>> {
+    %0 = "mhlo.constant"() {value = dense<[[1],[2],[3],[4],[5],[6],[7]]> : tensor<7x1xi64>} : () -> tensor<7x1xi64>
+    %size = builtin.unrealized_conversion_cast to tensor<i32>
+    %1 = "mhlo.set_dimension_size"(%0, %size) <{dimension = 0 : i64}> : (tensor<7x1xi64>, tensor<i32>) -> tensor<?x1xi64, #mhlo.type_extensions<bounds = [7, ?]>>
+    %2 = "mhlo.reshape"(%1) : (tensor<?x1xi64, #mhlo.type_extensions<bounds = [7, ?]>>)
+        -> tensor<?xi64, #mhlo.type_extensions<bounds = [7]>>
+    return %2 : tensor<?xi64, #mhlo.type_extensions<bounds = [7]>>
+}
+
+// -----
+
 // CHECK-LABEL: func @reverse
 func.func @reverse(%operand: tensor<3x2xi32>) -> tensor<3x2xi32> {
   %0 = "mhlo.reverse"(%operand) {

xla/mlir_hlo/tests/Dialect/mhlo/stablehlo-legalize-to-hlo.mlir

@@ -1355,6 +1355,13 @@ func.func @op_reshape(%arg0: tensor<16xf32>) -> tensor<4x4xf32> {
   func.return %0 : tensor<4x4xf32>
 }
 
+// CHECK-LABEL: "op_reshape_dynamic"
+func.func @op_reshape_dynamic(%arg0: tensor<?x1xi64, #mhlo.type_extensions<bounds = [7, ?]>>) -> tensor<7xi64> {
+  // CHECK: "mhlo.reshape"({{.*}}) : (tensor<?x1xi64, #mhlo.type_extensions<bounds = [7, ?]>>) -> tensor<7xi64>
+  %0 = "stablehlo.reshape"(%arg0) : (tensor<?x1xi64, #mhlo.type_extensions<bounds = [7, ?]>>) -> tensor<7xi64>
+  return %0 : tensor<7xi64>
+}
+
 // CHECK-LABEL: "op_return"
 func.func @op_return(%arg0: tensor<i32>, %arg1: tensor<f32>) -> tensor<f32> {
   //      CHECK: "mhlo.case"([[ARG0:%arg[0-9]+]]) ({