[mlir][Affine] Handle null parent op in getAffineParallelInductionVarOwner (#142025)

The issue occurs during a downstream pass which does dialect conversion,
where both
[`FuncOpConversion`](https://github.com/llvm/llvm-project/blob/cde67b6663f994fcb4ded28fd79b23a13d347c4a/mlir/lib/Conversion/FuncToLLVM/FuncToLLVM.cpp#L480)
and
[`SubviewFolder`](https://github.com/llvm/llvm-project/blob/cde67b6663f994fcb4ded28fd79b23a13d347c4a/mlir/lib/Dialect/MemRef/Transforms/ExpandStridedMetadata.cpp#L187)
are run together. The original starting IR is:
```mlir
module {
  func.func @foo(%arg0: memref<100x100xf32>, %arg1: index, %arg2: index, %arg3: index, %arg4: index) -> memref<?x?xf32, strided<[100, 1], offset: ?>> {
    %subview = memref.subview %arg0[%arg1, %arg2] [%arg3, %arg4] [1, 1] : memref<100x100xf32> to memref<?x?xf32, strided<[100, 1], offset: ?>>
    return %subview : memref<?x?xf32, strided<[100, 1], offset: ?>>
  }
}
```


After `FuncOpConversion` runs, the IR looks like:
```mlir
"builtin.module"() ({
  "llvm.func"() <{CConv = #llvm.cconv<ccc>, function_type = !llvm.func<struct<(ptr, ptr, i64, array<2 x i64>, array<2 x i64>)> (ptr, ptr, i64, i64, i64, i64, i64, i64, i64, i64, i64)>, linkage = #llvm.linkage<external>, sym_name = "foo", visibility_ = 0 : i64}> ({
  ^bb0(%arg0: !llvm.ptr, %arg1: !llvm.ptr, %arg2: i64, %arg3: i64, %arg4: i64, %arg5: i64, %arg6: i64, %arg7: i64, %arg8: i64, %arg9: i64, %arg10: i64):
    %0 = "memref.subview"(<<UNKNOWN SSA VALUE>>, <<UNKNOWN SSA VALUE>>, <<UNKNOWN SSA VALUE>>, <<UNKNOWN SSA VALUE>>, <<UNKNOWN SSA VALUE>>) <{operandSegmentSizes = array<i32: 1, 2, 2, 0>, static_offsets = array<i64: -9223372036854775808, -9223372036854775808>, static_sizes = array<i64: -9223372036854775808, -9223372036854775808>, static_strides = array<i64: 1, 1>}> : (memref<100x100xf32>, index, index, index, index) -> memref<?x?xf32, strided<[100, 1], offset: ?>>
    "func.return"(%0) : (memref<?x?xf32, strided<[100, 1], offset: ?>>) -> ()
  }) : () -> ()
  "func.func"() <{function_type = (memref<100x100xf32>, index, index, index, index) -> memref<?x?xf32, strided<[100, 1], offset: ?>>, sym_name = "foo"}> ({
  }) : () -> ()
}) {llvm.data_layout = "", llvm.target_triple = ""} : () -> ()
```
The `<<UNKNOWN SSA VALUE>>`'s here are block arguments of a separate
unlinked block, which is disconnected from the rest of the IR (so not
only is the IR verifier-invalid, it can't even be parsed). This IR is
created by signature conversion in the dialect conversion infra.

Now `SubviewFolder` is applied, and the utility function here is called
on one of these disconnected block arguments, causing a crash.

The TestMemRefToLLVMWithTransforms pass is introduced to exercise the
bug, and it can be reused by other contributors in the future.

---------

Signed-off-by: hanhanW <[email protected]>

Co-authored-by: Rahul Kayaith <[email protected]>

Author: hanhanW

mlir/lib/Dialect/Affine/IR/AffineOps.cpp

@@ -2667,7 +2667,7 @@ AffineParallelOp mlir::affine::getAffineParallelInductionVarOwner(Value val) {
   if (!ivArg || !ivArg.getOwner())
     return nullptr;
   Operation *containingOp = ivArg.getOwner()->getParentOp();
-  auto parallelOp = dyn_cast<AffineParallelOp>(containingOp);
+  auto parallelOp = dyn_cast_if_present<AffineParallelOp>(containingOp);
   if (parallelOp && llvm::is_contained(parallelOp.getIVs(), val))
     return parallelOp;
   return nullptr;

mlir/test/Conversion/MemRefToLLVM/memref-to-llvm-with-transforms.mlir

@@ -0,0 +1,10 @@
+// RUN: mlir-opt -test-memref-to-llvm-with-transforms %s | FileCheck %s
+
+// Checks that the program does not crash. The functionality of the pattern is
+// already checked in test/Dialect/MemRef/*.mlir
+
+func.func @subview_folder(%arg0: memref<100x100xf32>, %arg1: index, %arg2: index, %arg3: index, %arg4: index) -> memref<?x?xf32, strided<[100, 1], offset: ?>> {
+  %subview = memref.subview %arg0[%arg1, %arg2] [%arg3, %arg4] [1, 1] : memref<100x100xf32> to memref<?x?xf32, strided<[100, 1], offset: ?>>
+  return %subview : memref<?x?xf32, strided<[100, 1], offset: ?>>
+}
+// CHECK-LABEL: llvm.func @subview_folder

mlir/test/lib/Conversion/CMakeLists.txt

@@ -1,4 +1,5 @@
 add_subdirectory(ConvertToSPIRV)
 add_subdirectory(FuncToLLVM)
 add_subdirectory(MathToVCIX)
+add_subdirectory(MemRefToLLVM)
 add_subdirectory(VectorToSPIRV)

mlir/test/lib/Conversion/MemRefToLLVM/CMakeLists.txt

@@ -0,0 +1,21 @@
+# Exclude tests from libMLIR.so
+add_mlir_library(MLIRTestMemRefToLLVMWithTransforms
+  TestMemRefToLLVMWithTransforms.cpp
+
+  EXCLUDE_FROM_LIBMLIR
+
+  LINK_LIBS PUBLIC
+  MLIRTestDialect
+  )
+mlir_target_link_libraries(MLIRTestFuncToLLVM PUBLIC
+  MLIRLLVMCommonConversion
+  MLIRLLVMDialect
+  MLIRMemRefTransforms
+  MLIRPass
+  )
+
+target_include_directories(MLIRTestFuncToLLVM
+  PRIVATE
+  ${CMAKE_CURRENT_SOURCE_DIR}/../../Dialect/Test
+  ${CMAKE_CURRENT_BINARY_DIR}/../../Dialect/Test
+  )

mlir/test/lib/Conversion/MemRefToLLVM/TestMemRefToLLVMWithTransforms.cpp

@@ -0,0 +1,62 @@
+//===- TestMemRefToLLVMWithTransforms.cpp ---------------------------------===//
+//
+// 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/Conversion/FuncToLLVM/ConvertFuncToLLVM.h"
+#include "mlir/Conversion/LLVMCommon/ConversionTarget.h"
+#include "mlir/Conversion/LLVMCommon/LoweringOptions.h"
+#include "mlir/Conversion/LLVMCommon/TypeConverter.h"
+#include "mlir/Conversion/MemRefToLLVM/MemRefToLLVM.h"
+#include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
+#include "mlir/Dialect/MemRef/Transforms/Transforms.h"
+#include "mlir/IR/PatternMatch.h"
+#include "mlir/Pass/Pass.h"
+
+using namespace mlir;
+
+namespace {
+
+struct TestMemRefToLLVMWithTransforms
+    : public PassWrapper<TestMemRefToLLVMWithTransforms,
+                         OperationPass<ModuleOp>> {
+  MLIR_DEFINE_EXPLICIT_INTERNAL_INLINE_TYPE_ID(TestMemRefToLLVMWithTransforms)
+
+  void getDependentDialects(DialectRegistry &registry) const final {
+    registry.insert<LLVM::LLVMDialect>();
+  }
+
+  StringRef getArgument() const final {
+    return "test-memref-to-llvm-with-transforms";
+  }
+
+  StringRef getDescription() const final {
+    return "Tests conversion of MemRef dialects + `func.func` to LLVM dialect "
+           "with MemRef transforms.";
+  }
+
+  void runOnOperation() override {
+    MLIRContext *ctx = &getContext();
+    LowerToLLVMOptions options(ctx);
+    LLVMTypeConverter typeConverter(ctx, options);
+    RewritePatternSet patterns(ctx);
+    memref::populateExpandStridedMetadataPatterns(patterns);
+    populateFuncToLLVMConversionPatterns(typeConverter, patterns);
+    LLVMConversionTarget target(getContext());
+    if (failed(applyPartialConversion(getOperation(), target,
+                                      std::move(patterns))))
+      signalPassFailure();
+  }
+};
+
+} // namespace
+
+namespace mlir::test {
+void registerTestMemRefToLLVMWithTransforms() {
+  PassRegistration<TestMemRefToLLVMWithTransforms>();
+}
+} // namespace mlir::test

mlir/tools/mlir-opt/CMakeLists.txt

@@ -28,6 +28,7 @@ if(MLIR_INCLUDE_TESTS)
     MLIRMathTestPasses
     MLIRTestMathToVCIX
     MLIRMemRefTestPasses
+    MLIRTestMemRefToLLVMWithTransforms
     MLIRMeshTest
     MLIRNVGPUTestPasses
     MLIRSCFTestPasses

mlir/tools/mlir-opt/mlir-opt.cpp

@@ -130,6 +130,7 @@ void registerTestMathToVCIXPass();
 void registerTestIrdlTestDialectConversionPass();
 void registerTestMemRefDependenceCheck();
 void registerTestMemRefStrideCalculation();
+void registerTestMemRefToLLVMWithTransforms();
 void registerTestMeshReshardingSpmdizationPass();
 void registerTestMeshSimplificationsPass();
 void registerTestMultiBuffering();
@@ -275,6 +276,7 @@ void registerTestPasses() {
   mlir::test::registerTestMathToVCIXPass();
   mlir::test::registerTestMemRefDependenceCheck();
   mlir::test::registerTestMemRefStrideCalculation();
+  mlir::test::registerTestMemRefToLLVMWithTransforms();
   mlir::test::registerTestMeshReshardingSpmdizationPass();
   mlir::test::registerTestMeshSimplificationsPass();
   mlir::test::registerTestMultiBuffering();