[mlir][sparse] Fix a crash if block not have terminator (#180741)

This PR fixes a crash in `verifyNumBlockArgs` if region not end with a
terminator. Fixes #180720.

mlir/lib/Dialect/SparseTensor/IR/SparseTensorDialect.cpp

diff --git a/mlir/lib/Dialect/SparseTensor/IR/SparseTensorDialect.cpp b/mlir/lib/Dialect/SparseTensor/IR/SparseTensorDialect.cpp
index f6a707f..3a34ad9 100644
--- a/mlir/lib/Dialect/SparseTensor/IR/SparseTensorDialect.cpp
+++ b/mlir/lib/Dialect/SparseTensor/IR/SparseTensorDialect.cpp
@@ -1746,7 +1746,12 @@
       return op->emitError() << regionName << " region argument " << (i + 1)
                              << " type mismatch";
   }
-  Operation *term = region.front().getTerminator();
+  Block &block = region.front();
+  if (!block.mightHaveTerminator())
+    return op->emitError() << regionName
+                           << " region must end with a terminator";
+
+  Operation *term = block.getTerminator();
   YieldOp yield = dyn_cast<YieldOp>(term);
   if (!yield)
     return op->emitError() << regionName

mlir/test/Dialect/SparseTensor/invalid.mlir

diff --git a/mlir/test/Dialect/SparseTensor/invalid.mlir b/mlir/test/Dialect/SparseTensor/invalid.mlir
index 4c37fc6..30c74bb 100644
--- a/mlir/test/Dialect/SparseTensor/invalid.mlir
+++ b/mlir/test/Dialect/SparseTensor/invalid.mlir
@@ -631,6 +631,20 @@
 
 // -----
 
+func.func @invalid_reduce_wrong_terminator(%arg0: f64, %arg1: f64) -> f64 {
+  %cf1 = arith.constant 1.0 : f64
+  // expected-error@+1 {{reduce region must end with a terminator}}
+  %r = sparse_tensor.reduce %arg0, %arg1, %cf1 : f64 {
+  ^bb0(%arg2: f64, %arg3: f64):
+    %0 = arith.addf %arg2, %arg3 : f64
+    sparse_tensor.yield %0 : f64
+    %1 = arith.fptosi %0 : f64 to i32
+  }
+  return %r : f64
+}
+
+// -----
+
 func.func @invalid_select_num_args_mismatch(%arg0: f64) -> f64 {
   // expected-error@+1 {{select region must have exactly 1 arguments}}
   %r = sparse_tensor.select %arg0 : f64 {