Emit named structs as STRUCT_NAMED instead of OPAQUE.

Named (non-literal) structs were always written with the OPAQUE record code
while still carrying their body operands. LLVM 5/7 require an OPAQUE record to
have no body and reject it with "Invalid record", so any module with a named
struct failed to round-trip. Use STRUCT_NAMED for structs with a body and
reserve OPAQUE for genuinely opaque ones.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
(cherry picked from commit 3694275)

Author: maleadt

llvm/lib/Bitcode/LegacyWriter/BitcodeWriter50.cpp

@@ -908,7 +908,10 @@ void ModuleBitcodeWriter50::writeTypeTable() {
         Code = bitc::TYPE_CODE_STRUCT_ANON;
         AbbrevToUse = StructAnonAbbrev;
       } else {
-        Code = bitc::TYPE_CODE_OPAQUE;
+        // A named struct with a body must use STRUCT_NAMED; OPAQUE is only for
+        // bodyless structs (LLVM 5/7 reject an OPAQUE record carrying a body).
+        Code = ST->isOpaque() ? bitc::TYPE_CODE_OPAQUE
+                              : bitc::TYPE_CODE_STRUCT_NAMED;
 
         // Emit the name if it is present.
         if (!ST->getName().empty())

llvm/lib/Bitcode/LegacyWriter/BitcodeWriter70.cpp

@@ -925,7 +925,10 @@ void ModuleBitcodeWriter70::writeTypeTable() {
         Code = bitc::TYPE_CODE_STRUCT_ANON;
         AbbrevToUse = StructAnonAbbrev;
       } else {
-        Code = bitc::TYPE_CODE_OPAQUE;
+        // A named struct with a body must use STRUCT_NAMED; OPAQUE is only for
+        // bodyless structs (LLVM 5/7 reject an OPAQUE record carrying a body).
+        Code = ST->isOpaque() ? bitc::TYPE_CODE_OPAQUE
+                              : bitc::TYPE_CODE_STRUCT_NAMED;
 
         // Emit the name if it is present.
         if (!ST->getName().empty())