Revert "[C++20][Modules][Serialization] Delay marking pending incompl… (#127136)

…ete decl chains until the end of `finishPendingActions`. (#121245)"

This reverts commit a9e249f.

Reverting this change because of issue #126973.

(cherry picked from commit 912b154)

Author: zixu-w

clang/lib/Serialization/ASTReader.cpp

@@ -10186,12 +10186,12 @@ void ASTReader::visitTopLevelModuleMaps(
 }
 
 void ASTReader::finishPendingActions() {
-  while (!PendingIdentifierInfos.empty() ||
-         !PendingDeducedFunctionTypes.empty() ||
-         !PendingDeducedVarTypes.empty() || !PendingDeclChains.empty() ||
-         !PendingMacroIDs.empty() || !PendingDeclContextInfos.empty() ||
-         !PendingUpdateRecords.empty() ||
-         !PendingObjCExtensionIvarRedeclarations.empty()) {
+  while (
+      !PendingIdentifierInfos.empty() || !PendingDeducedFunctionTypes.empty() ||
+      !PendingDeducedVarTypes.empty() || !PendingIncompleteDeclChains.empty() ||
+      !PendingDeclChains.empty() || !PendingMacroIDs.empty() ||
+      !PendingDeclContextInfos.empty() || !PendingUpdateRecords.empty() ||
+      !PendingObjCExtensionIvarRedeclarations.empty()) {
     // If any identifiers with corresponding top-level declarations have
     // been loaded, load those declarations now.
     using TopLevelDeclsMap =
@@ -10239,6 +10239,13 @@ void ASTReader::finishPendingActions() {
     }
     PendingDeducedVarTypes.clear();
 
+    // For each decl chain that we wanted to complete while deserializing, mark
+    // it as "still needs to be completed".
+    for (unsigned I = 0; I != PendingIncompleteDeclChains.size(); ++I) {
+      markIncompleteDeclChain(PendingIncompleteDeclChains[I]);
+    }
+    PendingIncompleteDeclChains.clear();
+
     // Load pending declaration chains.
     for (unsigned I = 0; I != PendingDeclChains.size(); ++I)
       loadPendingDeclChain(PendingDeclChains[I].first,
@@ -10476,12 +10483,6 @@ void ASTReader::finishPendingActions() {
   for (auto *ND : PendingMergedDefinitionsToDeduplicate)
     getContext().deduplicateMergedDefinitonsFor(ND);
   PendingMergedDefinitionsToDeduplicate.clear();
-
-  // For each decl chain that we wanted to complete while deserializing, mark
-  // it as "still needs to be completed".
-  for (Decl *D : PendingIncompleteDeclChains)
-    markIncompleteDeclChain(D);
-  PendingIncompleteDeclChains.clear();
 }
 
 void ASTReader::diagnoseOdrViolations() {