Constrain mhlo.const to static shaped tensors.

Constants of unknown shape cannot be materialized. In most cases, one likely wants to use a scalar constant and rely on broadcasting instead.

PiperOrigin-RevId: 324252475

include/mlir-hlo/Dialect/mhlo/IR/hlo_ops.td

@@ -52,7 +52,7 @@ def HLO_ConstOp : HLO_Op<"constant",
   );
 
   let results = (outs
-    HLO_Tensor:$output
+    HLO_StaticShapeTensor:$output
   );
 
   let builders = [OpBuilder<

tests/ops.mlir

@@ -939,7 +939,23 @@ func @constants() -> () {
 
 func @constant_invalid() -> () {
   // expected-error@+1 {{op failed to verify that all of {value, output} have same type}}
-  %0 = "mhlo.constant"() {value = dense<0> : tensor<i32>} : () -> (tensor<*xi32>)
+  %0 = "mhlo.constant"() {value = dense<0> : tensor<i32>} : () -> (tensor<3xi32>)
+  return
+}
+
+// -----
+
+func @constant_invalid() -> () {
+  // expected-error@+1 {{op result #0 must be statically shaped tensor}}
+  %0 = "mhlo.constant"() {value = dense<1> : tensor<i32>} : () -> tensor<?xi32>
+  return
+}
+
+// -----
+
+func @constant_invalid() -> () {
+  // expected-error@+1 {{elements literal type must have static shape}}
+  %0 = "mhlo.constant"() {value = dense<1> : tensor<?xi32>} : () -> tensor<?xi32>
   return
 }