[mlir][spirv] Fix null pointer dereference in `--test-spirv-target-env`

[kuhar]

Summary

Fixes: https://github.com/llvm/llvm-project/issues/61710

mlir/test/Dialect/SPIRV/IR/target-env.mlir

-// RUN: mlir-opt -mlir-disable-threading -test-spirv-target-env %s | FileCheck %s
+// RUN: mlir-opt --split-input-file --verify-diagnostics --mlir-disable-threading \
+// RUN:   --test-spirv-target-env %s | FileCheck %s
 
 // Note: The following tests check that a spirv.target_env can properly control
 // the conversion target and filter unavailable ops during the conversion.
 // We don't care about the op argument consistency too much; so certain enum
 // values for enum attributes may not make much sense for the test op.
 
 // spirv.AtomicCompareExchangeWeak is available from SPIR-V 1.0 to 1.3 under
 // Kernel capability.

 
 // PhysicalStorageBuffer64 addressing model is available via extension
 // SPV_EXT_physical_storage_buffer or SPV_KHR_physical_storage_buffer;
 // both extensions are incorporated into SPIR-V 1.5.
 
 // Vulkan memory model is available via extension SPV_KHR_vulkan_memory_model,
 // which extensions are incorporated into SPIR-V 1.5.
 
+
+// expected-error @+1 {{missing 'spirv.target_env' attribute}}
+func.func @main() {
+  return
+}
+
+// -----
+
 //===----------------------------------------------------------------------===//
 // MaxVersion
 //===----------------------------------------------------------------------===//
 
 // CHECK-LABEL: @cmp_exchange_weak_suitable_version_capabilities
 func.func @cmp_exchange_weak_suitable_version_capabilities(%ptr: !spirv.ptr<i32, Workgroup>, %value: i32, %comparator: i32) -> i32 attributes {
   spirv.target_env = #spirv.target_env<#spirv.vce<v1.1, [Kernel, AtomicStorage], []>, #spirv.resource_limits<>>
 } {

mlir/test/lib/Dialect/SPIRV/TestAvailability.cpp

 //===- TestAvailability.cpp - Pass to test SPIR-V op availability ---------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/Dialect/SPIRV/IR/SPIRVAttributes.h"
 #include "mlir/Dialect/SPIRV/IR/SPIRVOps.h"
 #include "mlir/Dialect/SPIRV/Transforms/SPIRVConversion.h"
 #include "mlir/Pass/Pass.h"
 
 using namespace mlir;
 
 //===----------------------------------------------------------------------===//
 // Printing op availability pass
struct ConvertToIntegerDotProd : RewritePattern {
   }
 };
 } // namespace
 
 void ConvertToTargetEnv::runOnOperation() {
   MLIRContext *context = &getContext();
   func::FuncOp fn = getOperation();
 
-  auto targetEnv = fn.getOperation()
-                       ->getAttr(spirv::getTargetEnvAttrName())
-                       .cast<spirv::TargetEnvAttr>();
+  auto targetEnv = dyn_cast_or_null<spirv::TargetEnvAttr>(
+      fn.getOperation()->getAttr(spirv::getTargetEnvAttrName()));
   if (!targetEnv) {
     fn.emitError("missing 'spirv.target_env' attribute");
     return signalPassFailure();
   }
 
   auto target = SPIRVConversionTarget::get(targetEnv);
 
   static constexpr char sDotTestOpName[] = "test.convert_to_sdot_op";