[MLIR][LLVM] Fix recursive DI type export memory leak (#88122)

Followup to discussion
#87295 (comment).

The export cache should not cache temporary nodes.

Author: zyx-billy

mlir/lib/Target/LLVMIR/DebugTranslation.cpp

@@ -352,7 +352,8 @@ llvm::DINode *DebugTranslation::translate(DINodeAttr attr) {
                      DISubroutineTypeAttr>(
                    [&](auto attr) { return translateImpl(attr); });
 
-  attrToNode.insert({attr, node});
+  if (node && !node->isTemporary())
+    attrToNode.insert({attr, node});
   return node;
 }
 

mlir/test/Target/LLVMIR/llvmir-debug.mlir

@@ -442,12 +442,16 @@ llvm.mlir.global @global_variable() {dbg_expr = #di_global_variable_expression}
 #di_subprogram = #llvm.di_subprogram<scope = #di_file, file = #di_file, subprogramFlags = Optimized, type = #di_subroutine_type>
 #di_composite_type = #llvm.di_composite_type<tag = DW_TAG_class_type, recId = distinct[0]<>, scope = #di_subprogram>
 
-#di_global_variable = #llvm.di_global_variable<file = #di_file, line = 1, type = #di_composite_type>
+// Use the inner type standalone outside too. Ensures it's not cached wrong.
+#di_var_type = #llvm.di_subroutine_type<types = #di_composite_type, #di_composite_type_inner>
+#di_global_variable = #llvm.di_global_variable<file = #di_file, line = 1, type = #di_var_type>
 #di_global_variable_expression = #llvm.di_global_variable_expression<var = #di_global_variable>
 
 llvm.mlir.global @global_variable() {dbg_expr = #di_global_variable_expression} : !llvm.struct<()>
 
-// CHECK: distinct !DIGlobalVariable({{.*}}type: ![[COMP:[0-9]+]],
+// CHECK: distinct !DIGlobalVariable({{.*}}type: ![[VAR:[0-9]+]],
+// CHECK: ![[VAR]] = !DISubroutineType(types: ![[COMPS:[0-9]+]])
+// CHECK: ![[COMPS]] = !{![[COMP:[0-9]+]],
 // CHECK: ![[COMP]] = distinct !DICompositeType({{.*}}scope: ![[SCOPE:[0-9]+]],
 // CHECK: ![[SCOPE]] = !DISubprogram({{.*}}type: ![[SUBROUTINE:[0-9]+]],
 // CHECK: ![[SUBROUTINE]] = !DISubroutineType(types: ![[SR_TYPES:[0-9]+]])