[mlir] Add inliner interface to the index dialect (#170459)

Add the inliner interface to the index dialect allowing the `inline`
pass to inline all index operations.

mlir/lib/Dialect/Index/IR/IndexDialect.cpp

diff --git a/mlir/lib/Dialect/Index/IR/IndexDialect.cpp b/mlir/lib/Dialect/Index/IR/IndexDialect.cpp
index 183d0e3..887e8e1 100644
--- a/mlir/lib/Dialect/Index/IR/IndexDialect.cpp
+++ b/mlir/lib/Dialect/Index/IR/IndexDialect.cpp
@@ -8,6 +8,7 @@
 
 #include "mlir/Dialect/Index/IR/IndexDialect.h"
 #include "mlir/Conversion/ConvertToLLVM/ToLLVMInterface.h"
+#include "mlir/Transforms/InliningUtils.h"
 
 using namespace mlir;
 using namespace mlir::index;
@@ -15,10 +16,23 @@
 //===----------------------------------------------------------------------===//
 // IndexDialect
 //===----------------------------------------------------------------------===//
+namespace {
+/// This class defines the interface for handling inlining for index
+/// dialect operations.
+struct IndexInlinerInterface : public DialectInlinerInterface {
+  using DialectInlinerInterface::DialectInlinerInterface;
+
+  /// All index dialect ops can be inlined.
+  bool isLegalToInline(Operation *, Region *, bool, IRMapping &) const final {
+    return true;
+  }
+};
+} // namespace
 
 void IndexDialect::initialize() {
   registerAttributes();
   registerOperations();
+  addInterfaces<IndexInlinerInterface>();
   declarePromisedInterface<ConvertToLLVMPatternInterface, IndexDialect>();
 }
 

mlir/test/Dialect/Index/inliner-interface.mlir

diff --git a/mlir/test/Dialect/Index/inliner-interface.mlir b/mlir/test/Dialect/Index/inliner-interface.mlir
new file mode 100644
index 0000000..4c3d106
--- /dev/null
+++ b/mlir/test/Dialect/Index/inliner-interface.mlir
@@ -0,0 +1,15 @@
+// RUN: mlir-opt %s -inline | FileCheck %s
+
+// CHECK-LABEL: @main
+func.func @main(%arg0: i32) -> index {
+  // CHECK-NOT: call
+  // CHECK: index.castu
+  %0 = call @f(%arg0) : (i32) -> index
+  return %0 : index
+}
+
+// CHECK-LABEL: @f
+func.func @f(%arg0: i32) -> index {
+  %0 = index.castu %arg0 : i32 to index
+  return %0 : index
+}