[mlir][tosa] Robustify Tosa_IfOp against null dereference and wrong assertion (#159756)

Fixes  #159650.

The current implementation ICE out if we access an IfOp's terminator
when it doesn't have it. Instead the PR defers the job of verifying that
a block would have at least a terminator.

The current implementation also crashes with cast<YieldOp> if the
terminator is not a YieldOp, the PR also defers the job of verification
to the op itself.

Author: badumbatish

mlir/lib/Dialect/Tosa/IR/TosaOps.cpp

@@ -4025,19 +4025,27 @@ LogicalResult IfOp::verify() {
           .failed())
     return failure();
 
-  auto thenYield = cast<tosa::YieldOp>(getThenGraph().front().getTerminator());
-  if (errorIfTypeOrShapeMismatch(*this, thenYield.getInputs(),
-                                 "'then_graph' results", getOutputList(),
-                                 "'output_list'")
-          .failed())
-    return failure();
+  // MLIR will verify the absence of the terminator for us if otherwise.
+  if (getThenGraph().front().mightHaveTerminator()) {
+    auto thenYield =
+        dyn_cast<tosa::YieldOp>(getThenGraph().front().getTerminator());
+    if (thenYield && errorIfTypeOrShapeMismatch(
+                         *this, thenYield.getInputs(), "'then_graph' results",
+                         getOutputList(), "'output_list'")
+                         .failed())
+      return failure();
+  }
 
-  auto elseYield = cast<tosa::YieldOp>(getElseGraph().front().getTerminator());
-  if (errorIfTypeOrShapeMismatch(*this, elseYield.getInputs(),
-                                 "'else_graph' results", getOutputList(),
-                                 "'output_list'")
-          .failed())
-    return failure();
+  // MLIR will verify the absence of the terminator for us if otherwise.
+  if (getElseGraph().front().mightHaveTerminator()) {
+    auto elseYield =
+        dyn_cast<tosa::YieldOp>(getElseGraph().front().getTerminator());
+    if (elseYield && errorIfTypeOrShapeMismatch(
+                         *this, elseYield.getInputs(), "'else_graph' results",
+                         getOutputList(), "'output_list'")
+                         .failed())
+      return failure();
+  }
 
   auto condType = getCondition().getType();
   if (errorIfShapeNotSizeOne(*this, condType).failed())

mlir/test/Dialect/Tosa/verifier.mlir

@@ -438,6 +438,43 @@ func.func @test_pad_invalid_padding_value(%arg0: tensor<10xi8>, %arg1: tensor<1x
   return %1 : tensor<10xi8>
 }
 
+// -----
+func.func @test_cond_if_wrong_terminator_op(%arg0: tensor<i1>) -> tensor<i32> {
+  %0 = "tosa.cond_if"(%arg0) ({
+    %1 = "tosa.const"() <{values = dense<1> : tensor<i32>}> : () -> tensor<i32>
+    "tosa.yield"(%1) : (tensor<i32>) -> ()
+  }, {
+    // expected-error@+2 {{'func.return' op expects parent op 'func.func'}}
+    %2 = "tosa.const"() <{values = dense<2> : tensor<i32>}> : () -> tensor<i32>
+    "func.return"(%2) : (tensor<i32>) -> ()
+  }) : (tensor<i1>) -> tensor<i32>
+  return %0 : tensor<i32>
+}
+
+// -----
+func.func @test_cond_if_missing_then_terminator(%arg0: tensor<i1>) -> tensor<i32> {
+  %0 = "tosa.cond_if"(%arg0) ({
+    // expected-error@+1 {{block with no terminator}}
+    %1 = "tosa.const"() <{values = dense<1> : tensor<i32>}> : () -> tensor<i32>
+  }, {
+    %2 = "tosa.const"() <{values = dense<2> : tensor<i32>}> : () -> tensor<i32>
+    "tosa.yield"(%2) : (tensor<i32>) -> ()
+  }) : (tensor<i1>) -> tensor<i32>
+  return %0 : tensor<i32>
+}
+
+// -----
+func.func @test_cond_if_missing_else_terminator(%arg0: tensor<i1>) -> tensor<i32> {
+  %0 = "tosa.cond_if"(%arg0) ({
+    %1 = "tosa.const"() <{values = dense<1> : tensor<i32>}> : () -> tensor<i32>
+    "tosa.yield"(%1) : (tensor<i32>) -> ()
+  }, {
+    // expected-error@+1 {{block with no terminator}}
+    %2 = "tosa.const"() <{values = dense<2> : tensor<i32>}> : () -> tensor<i32>
+  }) : (tensor<i1>) -> tensor<i32>
+  return %0 : tensor<i32>
+}
+
 // -----
 
 func.func @test_cond_if_input_list_mismatch_then_block(%arg0: tensor<f32>, %arg1: tensor<f32>, %arg2: tensor<i1>) -> tensor<f32> {