[mlir][debug] Handle DIImportedEntity. (#103055)

The `DIImporedEntity` can be used to represent imported entities like
C++'s namespace with using directive or fortran's moudule with use
statement.

This PR adds `DIImportedEntityAttr` and 2-way translation from
`DIImportedEntity` to `DIImportedEntityAttr` and vice versa.

When an entity is imported in a function, the `retainedNodes` field of
the `DISubprogram` contains all the imported nodes. See the C++ code and
the LLVM IR below.

```
void test() {
    using namespace n1;
 ...
}

!2 = !DINamespace(name: "n1", scope: null)
!16 = distinct !DISubprogram(name: "test", ..., retainedNodes: !19) !19 = !{!20}
!20 = !DIImportedEntity(tag: DW_TAG_imported_module, scope: !16, entity: !2 ...)
```

This PR makes sure that the translation from mlir to `retainedNodes`
field happens correctly both ways.

To side step the cyclic dependency between `DISubprogramAttr` and `DIImportedEntityAttr`,
we have decided to not have `scope` field in the `DIImportedEntityAttr` and it is inferred
from the entity which hold the list of `DIImportedEntityAttr`. A `retainedNodes` field has been
added in the `DISubprogramAttr` which contains the list of `DIImportedEntityAttr` for that
function.

This PR currently does not handle entities imported in a global scope
but that should be easy to handle in a subsequent PR.

Author: abidh

mlir/include/mlir-c/Dialect/LLVM.h

@@ -316,7 +316,8 @@ MLIR_CAPI_EXPORTED MlirAttribute mlirLLVMDISubprogramAttrGet(
     MlirContext ctx, MlirAttribute id, MlirAttribute compileUnit,
     MlirAttribute scope, MlirAttribute name, MlirAttribute linkageName,
     MlirAttribute file, unsigned int line, unsigned int scopeLine,
-    uint64_t subprogramFlags, MlirAttribute type);
+    uint64_t subprogramFlags, MlirAttribute type, intptr_t nRetainedNodes,
+    MlirAttribute const *retainedNodes);
 
 /// Gets the scope from this DISubprogramAttr.
 MLIR_CAPI_EXPORTED MlirAttribute
@@ -353,6 +354,12 @@ MLIR_CAPI_EXPORTED MlirAttribute mlirLLVMDIModuleAttrGet(
     MlirAttribute name, MlirAttribute configMacros, MlirAttribute includePath,
     MlirAttribute apinotes, unsigned int line, bool isDecl);
 
+/// Creates a LLVM DIImportedEntityAttr attribute.
+MLIR_CAPI_EXPORTED MlirAttribute mlirLLVMDIImportedEntityAttrGet(
+    MlirContext ctx, unsigned int tag, MlirAttribute entity, MlirAttribute file,
+    unsigned int line, MlirAttribute name, intptr_t nElements,
+    MlirAttribute const *elements);
+
 /// Gets the scope of this DIModuleAttr.
 MLIR_CAPI_EXPORTED MlirAttribute
 mlirLLVMDIModuleAttrGetScope(MlirAttribute diModule);

mlir/lib/CAPI/Dialect/LLVM.cpp

@@ -293,14 +293,20 @@ MlirAttribute mlirLLVMDISubprogramAttrGet(
     MlirContext ctx, MlirAttribute id, MlirAttribute compileUnit,
     MlirAttribute scope, MlirAttribute name, MlirAttribute linkageName,
     MlirAttribute file, unsigned int line, unsigned int scopeLine,
-    uint64_t subprogramFlags, MlirAttribute type) {
+    uint64_t subprogramFlags, MlirAttribute type, intptr_t nRetainedNodes,
+    MlirAttribute const *retainedNodes) {
+  SmallVector<Attribute> nodesStorage;
+  nodesStorage.reserve(nRetainedNodes);
   return wrap(DISubprogramAttr::get(
       unwrap(ctx), cast<DistinctAttr>(unwrap(id)),
       cast<DICompileUnitAttr>(unwrap(compileUnit)),
       cast<DIScopeAttr>(unwrap(scope)), cast<StringAttr>(unwrap(name)),
       cast<StringAttr>(unwrap(linkageName)), cast<DIFileAttr>(unwrap(file)),
       line, scopeLine, DISubprogramFlags(subprogramFlags),
-      cast<DISubroutineTypeAttr>(unwrap(type))));
+      cast<DISubroutineTypeAttr>(unwrap(type)),
+      llvm::map_to_vector(
+          unwrapList(nRetainedNodes, retainedNodes, nodesStorage),
+          [](Attribute a) { return cast<DINodeAttr>(a); })));
 }
 
 MlirAttribute mlirLLVMDISubprogramAttrGetScope(MlirAttribute diSubprogram) {
@@ -345,3 +351,16 @@ MlirAttribute mlirLLVMDIModuleAttrGet(MlirContext ctx, MlirAttribute file,
 MlirAttribute mlirLLVMDIModuleAttrGetScope(MlirAttribute diModule) {
   return wrap(cast<DIModuleAttr>(unwrap(diModule)).getScope());
 }
+
+MlirAttribute mlirLLVMDIImportedEntityAttrGet(
+    MlirContext ctx, unsigned int tag, MlirAttribute entity, MlirAttribute file,
+    unsigned int line, MlirAttribute name, intptr_t nElements,
+    MlirAttribute const *elements) {
+  SmallVector<Attribute> elementsStorage;
+  elementsStorage.reserve(nElements);
+  return wrap(DIImportedEntityAttr::get(
+      unwrap(ctx), tag, cast<DINodeAttr>(unwrap(entity)),
+      cast<DIFileAttr>(unwrap(file)), line, cast<StringAttr>(unwrap(name)),
+      llvm::map_to_vector(unwrapList(nElements, elements, elementsStorage),
+                          [](Attribute a) { return cast<DINodeAttr>(a); })));
+}