[modules] Fix miscompilation when using two RecordDecl definitions with the same name.

When deserializing a RecordDecl we don't enforce that redeclaration
chain contains only a single definition. So if the canonical decl is not
a definition itself, `RecordType::getDecl` can return different objects
before and after an include. It means we can build CGRecordLayout for
one RecordDecl with its set of FieldDecl but try to use it with
FieldDecl belonging to a different RecordDecl. With assertions enabled
it results in

> Assertion failed: (FieldInfo.count(FD) && "Invalid field for record!"),
> function getLLVMFieldNo, file llvm-project/clang/lib/CodeGen/CGRecordLayout.h, line 199.

and with assertions disabled a bunch of fields are treated as their
memory is located at offset 0.

Fix by keeping the first encountered RecordDecl definition and marking
the subsequent ones as non-definitions. Also need to merge FieldDecl
properly, so that `getPrimaryMergedDecl` works correctly and during name
lookup we don't treat fields from same-name RecordDecl as ambiguous.

rdar://80184238

Differential Revision: https://reviews.llvm.org/D106994

Author: vsapsai

clang/include/clang/Serialization/ASTReader.h

@@ -1162,6 +1162,10 @@ class ASTReader
   /// definitions. Only populated when using modules in C++.
   llvm::DenseMap<EnumDecl *, EnumDecl *> EnumDefinitions;
 
+  /// A mapping from canonical declarations of records to their canonical
+  /// definitions. Doesn't cover CXXRecordDecl.
+  llvm::DenseMap<RecordDecl *, RecordDecl *> RecordDefinitions;
+
   /// When reading a Stmt tree, Stmt operands are placed in this stack.
   SmallVector<Stmt *, 16> StmtStack;
 

clang/lib/Serialization/ASTCommon.cpp

@@ -474,7 +474,7 @@ bool serialization::needsAnonymousDeclarationNumber(const NamedDecl *D) {
   // Otherwise, we only care about anonymous class members / block-scope decls.
   // FIXME: We need to handle lambdas and blocks within inline / templated
   // variables too.
-  if (D->getDeclName() || !isa<CXXRecordDecl>(D->getLexicalDeclContext()))
+  if (D->getDeclName() || !isa<RecordDecl>(D->getLexicalDeclContext()))
     return false;
   return isa<TagDecl>(D) || isa<FieldDecl>(D);
 }

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -332,7 +332,7 @@ namespace clang {
     RedeclarableResult VisitTagDecl(TagDecl *TD);
     void VisitEnumDecl(EnumDecl *ED);
     RedeclarableResult VisitRecordDeclImpl(RecordDecl *RD);
-    void VisitRecordDecl(RecordDecl *RD) { VisitRecordDeclImpl(RD); }
+    void VisitRecordDecl(RecordDecl *RD);
     RedeclarableResult VisitCXXRecordDeclImpl(CXXRecordDecl *D);
     void VisitCXXRecordDecl(CXXRecordDecl *D) { VisitCXXRecordDeclImpl(D); }
     RedeclarableResult VisitClassTemplateSpecializationDeclImpl(
@@ -808,6 +808,34 @@ ASTDeclReader::VisitRecordDeclImpl(RecordDecl *RD) {
   return Redecl;
 }
 
+void ASTDeclReader::VisitRecordDecl(RecordDecl *RD) {
+  VisitRecordDeclImpl(RD);
+
+  // Maintain the invariant of a redeclaration chain containing only
+  // a single definition.
+  if (RD->isCompleteDefinition()) {
+    RecordDecl *Canon = static_cast<RecordDecl *>(RD->getCanonicalDecl());
+    RecordDecl *&OldDef = Reader.RecordDefinitions[Canon];
+    if (!OldDef) {
+      // This is the first time we've seen an imported definition. Look for a
+      // local definition before deciding that we are the first definition.
+      for (auto *D : merged_redecls(Canon)) {
+        if (!D->isFromASTFile() && D->isCompleteDefinition()) {
+          OldDef = D;
+          break;
+        }
+      }
+    }
+    if (OldDef) {
+      Reader.MergedDeclContexts.insert(std::make_pair(RD, OldDef));
+      RD->setCompleteDefinition(false);
+      Reader.mergeDefinitionVisibility(OldDef, RD);
+    } else {
+      OldDef = RD;
+    }
+  }
+}
+
 void ASTDeclReader::VisitValueDecl(ValueDecl *VD) {
   VisitNamedDecl(VD);
   // For function declarations, defer reading the type in case the function has
@@ -2645,7 +2673,7 @@ static bool allowODRLikeMergeInC(NamedDecl *ND) {
   if (!ND)
     return false;
   // TODO: implement merge for other necessary decls.
-  if (isa<EnumConstantDecl>(ND))
+  if (isa<EnumConstantDecl, FieldDecl, IndirectFieldDecl>(ND))
     return true;
   return false;
 }
@@ -3315,6 +3343,9 @@ DeclContext *ASTDeclReader::getPrimaryContextForMerging(ASTReader &Reader,
     return DD->Definition;
   }
 
+  if (auto *RD = dyn_cast<RecordDecl>(DC))
+    return RD->getDefinition();
+
   if (auto *ED = dyn_cast<EnumDecl>(DC))
     return ED->getASTContext().getLangOpts().CPlusPlus? ED->getDefinition()
                                                       : nullptr;
@@ -3398,6 +3429,9 @@ ASTDeclReader::getPrimaryDCForAnonymousDecl(DeclContext *LexicalDC) {
     if (auto *MD = dyn_cast<ObjCMethodDecl>(D))
       if (MD->isThisDeclarationADefinition())
         return MD;
+    if (auto *RD = dyn_cast<RecordDecl>(D))
+      if (RD->isThisDeclarationADefinition())
+        return RD;
   }
 
   // No merged definition yet.

clang/test/Modules/Inputs/merge-record-definition/RecordDef.framework/Headers/RecordDef.h

@@ -0,0 +1,21 @@
+// It is important to have a definition *after* non-definition declaration.
+typedef struct _Buffer Buffer;
+struct _Buffer {
+  int a;
+  int b;
+  int c;
+};
+
+typedef struct _AnonymousStruct AnonymousStruct;
+struct _AnonymousStruct {
+  struct {
+    int x;
+    int y;
+  };
+};
+
+typedef union _UnionRecord UnionRecord;
+union _UnionRecord {
+  int u: 2;
+  int v: 4;
+};

clang/test/Modules/Inputs/merge-record-definition/RecordDef.framework/Modules/module.modulemap

@@ -0,0 +1,4 @@
+framework module RecordDef {
+  header "RecordDef.h"
+  export *
+}

clang/test/Modules/Inputs/merge-record-definition/RecordDefCopy.framework/Headers/RecordDefCopy.h

@@ -0,0 +1,21 @@
+// It is important to have a definition *after* non-definition declaration.
+typedef struct _Buffer Buffer;
+struct _Buffer {
+  int a;
+  int b;
+  int c;
+};
+
+typedef struct _AnonymousStruct AnonymousStruct;
+struct _AnonymousStruct {
+  struct {
+    int x;
+    int y;
+  };
+};
+
+typedef union _UnionRecord UnionRecord;
+union _UnionRecord {
+  int u: 2;
+  int v: 4;
+};

clang/test/Modules/Inputs/merge-record-definition/RecordDefCopy.framework/Modules/module.modulemap

@@ -0,0 +1,4 @@
+framework module RecordDefCopy {
+  header "RecordDefCopy.h"
+  export *
+}

clang/test/Modules/Inputs/merge-record-definition/RecordDefHidden.framework/Headers/Hidden.h

@@ -0,0 +1,21 @@
+// It is important to have a definition *after* non-definition declaration.
+typedef struct _Buffer Buffer;
+struct _Buffer {
+  int a;
+  int b;
+  int c;
+};
+
+typedef struct _AnonymousStruct AnonymousStruct;
+struct _AnonymousStruct {
+  struct {
+    int x;
+    int y;
+  };
+};
+
+typedef union _UnionRecord UnionRecord;
+union _UnionRecord {
+  int u: 2;
+  int v: 4;
+};

clang/test/Modules/Inputs/merge-record-definition/RecordDefHidden.framework/Headers/Visible.h

@@ -0,0 +1 @@
+// Empty header to create a module.

clang/test/Modules/Inputs/merge-record-definition/RecordDefHidden.framework/Modules/module.modulemap

@@ -0,0 +1,9 @@
+framework module RecordDefHidden {
+  header "Visible.h"
+  export *
+
+  explicit module Hidden {
+    header "Hidden.h"
+    export *
+  }
+}