[flang][NFC] do not copy fields in fir::RecordType::getTypeList (#145530)

For historical reason, `fir::RecordType::getTypeList` was returning an
std::vector, causing the entire field list to be copied when called.

It is called a lot indirectly in all type helpers, which themselves are
called a lot in derived type heavy code like WRF.
The `fir::hasDynamicType` helper is also called a lot, and it can just
check for length parameters to avoid looping on all derived type
components in most cases.

Author: jeanPerier

flang/include/flang/Optimizer/Dialect/FIRTypes.td

@@ -330,7 +330,8 @@ def fir_RecordType : FIR_Type<"Record", "type"> {
 
   let extraClassDeclaration = [{
     using TypePair = std::pair<std::string, mlir::Type>;
-    using TypeList = std::vector<TypePair>;
+    using TypeList = llvm::ArrayRef<TypePair>;
+    using TypeVector = llvm::SmallVector<TypePair>;
     TypeList getTypeList() const;
     TypeList getLenParamList() const;
 

flang/lib/Optimizer/Dialect/FIRType.cpp

@@ -261,6 +261,8 @@ mlir::Type dyn_cast_ptrOrBoxEleTy(mlir::Type t) {
 }
 
 static bool hasDynamicSize(fir::RecordType recTy) {
+  if (recTy.getLenParamList().empty())
+    return false;
   for (auto field : recTy.getTypeList()) {
     if (auto arr = mlir::dyn_cast<fir::SequenceType>(field.second)) {
       if (sequenceWithNonConstantShape(arr))
@@ -1006,7 +1008,7 @@ mlir::Type fir::RecordType::parse(mlir::AsmParser &parser) {
     return {};
   RecordType result = RecordType::get(parser.getContext(), name);
 
-  RecordType::TypeList lenParamList;
+  RecordType::TypeVector lenParamList;
   if (!parser.parseOptionalLParen()) {
     while (true) {
       llvm::StringRef lenparam;
@@ -1024,7 +1026,7 @@ mlir::Type fir::RecordType::parse(mlir::AsmParser &parser) {
       return {};
   }
 
-  RecordType::TypeList typeList;
+  RecordType::TypeVector typeList;
   if (!parser.parseOptionalLess()) {
     result.pack(true);
   }

flang/test/Fir/convert-to-llvm.fir

@@ -1817,8 +1817,8 @@ func.func private @custom_typeP.field_1.offset() -> i32
 func.func private @custom_typeP.field_2.offset() -> i32
 
 func.func @field_index_dynamic_size() -> () {
-  %1 = fir.field_index field_1, !fir.type<custom_type{field_1:i32, field_2:!fir.array<?xf32>}>
-  %2 = fir.field_index field_2, !fir.type<custom_type{field_1:i32, field_2:!fir.array<?xf32>}>
+  %1 = fir.field_index field_1, !fir.type<custom_type(l:i32){field_1:i32, field_2:!fir.array<?xf32>}>
+  %2 = fir.field_index field_2, !fir.type<custom_type(l:i32){field_1:i32, field_2:!fir.array<?xf32>}>
   return
 }