[llvm-branch-commits] [clang] [serialization] No transitive type change (PR #92511)

[Ilya Biryukov via llvm-branch-commits]

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@@ -70,38 +71,53 @@ using DeclID = DeclIDBase::DeclID;
 
 /// An ID number that refers to a type in an AST file.
 ///
-/// The ID of a type is partitioned into two parts: the lower
+/// The ID of a type is partitioned into three parts:
+/// - the lower
 /// three bits are used to store the const/volatile/restrict
-/// qualifiers (as with QualType) and the upper bits provide a
-/// type index. The type index values are partitioned into two
+/// qualifiers (as with QualType).
+/// - the upper 29 bits provide a type index in the corresponding
+/// module file.
+/// - the upper 32 bits provide a module file index.
+///
+/// The type index values are partitioned into two
 /// sets. The values below NUM_PREDEF_TYPE_IDs are predefined type
 /// IDs (based on the PREDEF_TYPE_*_ID constants), with 0 as a
 /// placeholder for "no type". Values from NUM_PREDEF_TYPE_IDs are
 /// other types that have serialized representations.
-using TypeID = uint32_t;
+using TypeID = uint64_t;
 
 /// A type index; the type ID with the qualifier bits removed.
+/// Keep structure alignment 32-bit since the blob is assumed as 32-bit
+/// aligned.
 class TypeIdx {
+  uint32_t ModuleFileIndex = 0;
   uint32_t Idx = 0;
 
 public:
   TypeIdx() = default;
-  explicit TypeIdx(uint32_t index) : Idx(index) {}
+  explicit TypeIdx(uint32_t Idx) : ModuleFileIndex(0), Idx(Idx) {}
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ilya-biryukov wrote:

Could we explicitly pass 0 to the ModuleFileIndex instead? It's very uncommon to have defaulted parameters at the start of the parameter list rather than at the end.

https://github.com/llvm/llvm-project/pull/92511