[CodeGen] Revamp counted_by calculations (#70606)

Break down the counted_by calculations so that they correctly handle
anonymous structs, which are specified internally as IndirectFieldDecls.

Improves the calculation of __bdos on a different field member in the struct.
And also improves support for __bdos in an index into the FAM. If the index
is further out than the length of the FAM, then we return __bdos's "can't
determine the size" value (zero or negative one, depending on type).

Also simplify the code to use helper methods to get the field referenced
by counted_by and the flexible array member itself, which also had some
issues with FAMs in sub-structs.

1 files changed, 10 insertions, 3 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index dc6773e..bb8c144 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -3022,11 +3022,18 @@ public:
   void EmitBoundsCheck(const Expr *E, const Expr *Base, llvm::Value *Index,
                        QualType IndexType, bool Accessed);
 
+  // Find a struct's flexible array member. It may be embedded inside multiple
+  // sub-structs, but must still be the last field.
+  const ValueDecl *FindFlexibleArrayMemberField(ASTContext &Ctx,
+                                                const RecordDecl *RD);
+
   /// Find the FieldDecl specified in a FAM's "counted_by" attribute. Returns
   /// \p nullptr if either the attribute or the field doesn't exist.
-  FieldDecl *FindCountedByField(
-      const Expr *Base,
-      LangOptions::StrictFlexArraysLevelKind StrictFlexArraysLevel);
+  const ValueDecl *FindCountedByField(const Expr *Base);
+
+  /// Build an expression accessing the "counted_by" field.
+  const Expr *BuildCountedByFieldExpr(const Expr *Base,
+                                      const ValueDecl *CountedByVD);
 
   llvm::Value *EmitScalarPrePostIncDec(const UnaryOperator *E, LValue LV,
                                        bool isInc, bool isPre);