Florian Weimer via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> On many architectures, there is a padding gap after the how array
> member, and cfa_how can be moved there. This reduces the size of the
> struct and the amount of memory that uw_frame_state_for has to clear.
>
> There is no measurable performance benefit from this on x86-64 (even
> though the memset goes from 120 to 112 bytes), but it seems to be a
> good idea to do anyway.
>
> libgcc/
>
> * unwind-dw2.h (struct frame_state_reg_info): Move cfa_how member
> and reduce its size.
OK, thanks.
Richard
>
> ---
> libgcc/unwind-dw2.h | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/libgcc/unwind-dw2.h b/libgcc/unwind-dw2.h
> index af34e000f07..a0834b18277 100644
> --- a/libgcc/unwind-dw2.h
> +++ b/libgcc/unwind-dw2.h
> @@ -50,6 +50,12 @@ typedef struct
> } reg[__LIBGCC_DWARF_FRAME_REGISTERS__+1];
> unsigned char how[__LIBGCC_DWARF_FRAME_REGISTERS__+1];
>
> + enum {
> + CFA_UNSET,
> + CFA_REG_OFFSET,
> + CFA_EXP
> + } cfa_how : 8;
> +
> /* Used to implement DW_CFA_remember_state. */
> struct frame_state_reg_info *prev;
>
> @@ -58,11 +64,6 @@ typedef struct
> _Unwind_Sword cfa_offset;
> _Unwind_Word cfa_reg;
> const unsigned char *cfa_exp;
> - enum {
> - CFA_UNSET,
> - CFA_REG_OFFSET,
> - CFA_EXP
> - } cfa_how;
> } regs;
>
> /* The PC described by the current frame state. */
>
> base-commit: 3dfeda095bd43c011fdc3834b9cec39bb9a73a1f
