[clang][Interp] Use first field decl for Record field lookup (#104412)

Author: tbaederr

clang/lib/AST/Interp/Program.cpp

@@ -329,6 +329,7 @@ Record *Program::getOrCreateRecord(const RecordDecl *RD) {
   // Reserve space for fields.
   Record::FieldList Fields;
   for (const FieldDecl *FD : RD->fields()) {
+    assert(FD == FD->getFirstDecl());
     // Note that we DO create fields and descriptors
     // for unnamed bitfields here, even though we later ignore
     // them everywhere. That's so the FieldDecl's getFieldIndex() matches.

clang/lib/AST/Interp/Record.cpp

@@ -37,7 +37,7 @@ const std::string Record::getName() const {
 }
 
 const Record::Field *Record::getField(const FieldDecl *FD) const {
-  auto It = FieldMap.find(FD);
+  auto It = FieldMap.find(FD->getFirstDecl());
   assert(It != FieldMap.end() && "Missing field");
   return It->second;
 }

clang/test/Modules/enum-codegen.cpp

@@ -1,5 +1,6 @@
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -triple %itanium_abi_triple -fmodules -fmodules-cache-path=%t %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple %itanium_abi_triple -fmodules -fmodules-cache-path=%t %s -emit-llvm -o - -fexperimental-new-constant-interpreter | FileCheck %s
 
 // CHECK: @{{.*var.*}} = {{.*}} %union.union_type { i8 1 },