On 6/9/25 6:12 PM, Joseph Myers wrote:
On Mon, 9 Jun 2025, Jakub Jelinek wrote:Hi! For C++26 P2786R13 I'm afraid I'll need 4 new flags on class types in struct lang_type (1 bit for trivially_relocatable_if_eligible, 1 for replaceable_if_eligible, 1 for not_trivially_relocatable and 1 for not_replaceable) and there are just 2 bits left. The following patch is an attempt to save 8 bytes of memory in those structures when not compiling ObjC or ObjC++ (I think those are used fairly rarely and the patch keeps the sizes unmodified for those 2). The old allocations were 32 bytes for C and 120 bytes for C++. The patch moves the objc_info member last in the C++ case (it was already last in the C case), arranges for GC to skip it for C and C++ but walk for ObjC and ObjC++ and allocates or copies over just offsetof bytes instead of sizeof. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2025-06-09 Jakub Jelinek <ja...@redhat.com> gcc/c/ * c-lang.h (union lang_type::maybe_objc_info): New type. (struct lang_type): Use union maybe_objc_info info member instead of tree objc_info. * c-decl.cc (finish_struct): Allocate struct lang_type using ggc_internal_cleared_alloc instead of ggc_cleared_alloc, and use sizeof (struct lang_type) for ObjC and otherwise offsetof (struct lang_type, info) as size. (finish_enum): Likewise.The C changes are OK.
C++ as well. Jason
