Re: [PATCH] c++: Fix up value initialization of structs with zero width bitfields [PR102019]
On 8/23/21 4:16 PM, Jakub Jelinek wrote: Hi! The removal of remove_zero_width_bit_fields, in addition to triggering some ABI issues that need solving anyway (ABI incompatibility between C and C++) also resulted in UB inside of gcc, we now call build_zero_init which calls build_int_cst on an integral type with TYPE_PRECISION of 0. Fixed by ignoring the zero width bitfields. I understand build_value_init_noctor wants to initialize to 0 even unnamed bitfields (of non-zero width), at least until we have some CONSTRUCTOR flag that says that even all the padding bits should be cleared. Bootstrapped/regtested on x86_64-linux, ok for trunk? OK. 2021-08-23 Jakub Jelinek PR c++/102019 * init.c (build_value_init_noctor): Ignore unnamed zero-width bitfields. --- gcc/cp/init.c.jj2021-07-29 13:24:42.698012879 +0200 +++ gcc/cp/init.c 2021-08-23 14:43:08.791947395 +0200 @@ -427,6 +427,11 @@ build_value_init_noctor (tree type, tsub == NULL_TREE)) continue; + /* Ignore unnamed zero-width bitfields. */ + if (DECL_UNNAMED_BIT_FIELD (field) + && integer_zerop (DECL_SIZE (field))) + continue; + /* We could skip vfields and fields of types with user-defined constructors, but I think that won't improve performance at all; it should be simpler in general just Jakub
[PATCH] c++: Fix up value initialization of structs with zero width bitfields [PR102019]
Hi! The removal of remove_zero_width_bit_fields, in addition to triggering some ABI issues that need solving anyway (ABI incompatibility between C and C++) also resulted in UB inside of gcc, we now call build_zero_init which calls build_int_cst on an integral type with TYPE_PRECISION of 0. Fixed by ignoring the zero width bitfields. I understand build_value_init_noctor wants to initialize to 0 even unnamed bitfields (of non-zero width), at least until we have some CONSTRUCTOR flag that says that even all the padding bits should be cleared. Bootstrapped/regtested on x86_64-linux, ok for trunk? 2021-08-23 Jakub Jelinek PR c++/102019 * init.c (build_value_init_noctor): Ignore unnamed zero-width bitfields. --- gcc/cp/init.c.jj2021-07-29 13:24:42.698012879 +0200 +++ gcc/cp/init.c 2021-08-23 14:43:08.791947395 +0200 @@ -427,6 +427,11 @@ build_value_init_noctor (tree type, tsub == NULL_TREE)) continue; + /* Ignore unnamed zero-width bitfields. */ + if (DECL_UNNAMED_BIT_FIELD (field) + && integer_zerop (DECL_SIZE (field))) + continue; + /* We could skip vfields and fields of types with user-defined constructors, but I think that won't improve performance at all; it should be simpler in general just Jakub
