[mlir][builtin] Make unrealized_conversion_cast inlineable (#139722)

Until now, `builtin.unrealized_conversion_cast` ops could not be inlined
by the Inliner pass.

Author: matthias-springer

mlir/lib/Transforms/Utils/InliningUtils.cpp

@@ -13,6 +13,7 @@
 #include "mlir/Transforms/InliningUtils.h"
 
 #include "mlir/IR/Builders.h"
+#include "mlir/IR/BuiltinOps.h"
 #include "mlir/IR/IRMapping.h"
 #include "mlir/IR/Operation.h"
 #include "mlir/Interfaces/CallInterfaces.h"
@@ -182,6 +183,11 @@ static bool isLegalToInline(InlinerInterface &interface, Region *src,
                             IRMapping &valueMapping) {
   for (auto &block : *src) {
     for (auto &op : block) {
+      // UnrealizedConversionCastOp is inlineable but cannot implement the
+      // inliner interface due to layering constraints.
+      if (isa<UnrealizedConversionCastOp>(op))
+        continue;
+
       // Check this operation.
       if (!interface.isLegalToInline(&op, insertRegion,
                                      shouldCloneInlinedRegion, valueMapping)) {

mlir/test/Transforms/inlining.mlir

@@ -5,14 +5,18 @@
 // RUN: mlir-opt %s -inline='op-pipelines=func.func(canonicalize,cse)' | FileCheck %s --check-prefix INLINE_SIMPLIFY
 
 // Inline a function that takes an argument.
-func.func @func_with_arg(%c : i32) -> i32 {
-  %b = arith.addi %c, %c : i32
-  return %b : i32
+func.func @func_with_arg(%arg0 : i32) -> i32 {
+  %b = arith.addi %arg0, %arg0 : i32
+  %c = builtin.unrealized_conversion_cast %b : i32 to i64
+  %d = builtin.unrealized_conversion_cast %c : i64 to i32
+  return %d : i32
 }
 
 // CHECK-LABEL: func @inline_with_arg
 func.func @inline_with_arg(%arg0 : i32) -> i32 {
   // CHECK-NEXT: arith.addi
+  // CHECK-NEXT: unrealized_conversion_cast
+  // CHECK-NEXT: unrealized_conversion_cast
   // CHECK-NEXT: return
 
   %0 = call @func_with_arg(%arg0) : (i32) -> i32