Re: [PATCH] Shrink size of dwarf2_per_cu_data

[Tom Tromey <tom@tromey.com>]

>>>>> "Gary" == Gary Benson <gbenson@redhat.com> writes:

Gary> Tom Tromey wrote:
>> I noticed some holes in struct dwarf2_per_cu_data.  This patch
>> rearranges the type slightly, and shrinks the size of some fields.
>> This reduces it from 136 bytes to 112 bytes (on x86-64).

Gary> Nice.  Though I'd assumed the compiler would do this.

C and C++ compilers can't generally do this, though other languages like
Rust and Ada do allow it.

>> I also reduced the size of the DWARF "version" fields in a couple of
>> spots.  It seemed needless to use a short to hold a value that
>> ranges from 2 to 5, and this also helped the goal of shrinking
>> dwarf2_per_cu_data.

Gary> There's other things in there if you were going that way, e.g.:

Gary>   unsigned char addr_size;
Gary>   unsigned char signed_addr_p;
Gary>   sect_offset abbrev_sect_off;

Gary>   /* Size of file offsets; either 4 or 8.  */
Gary>   unsigned int offset_size;

Gary>   /* Size of the length field; either 4 or 12.  */
Gary>   unsigned int initial_length_size;

Gary> I presume you'd need to lose 8 whole bytes to shrink the struct
Gary> further, so marking these as <8bit values probably wouldn't help
Gary> any, but maybe it's worth it?

I looked at this, and it doesn't remove enough space to help.
Might still be worth doing for clarity, I dunno.

Gary> How many CUs does something big
Gary> have?

gdb has 1197 as of today, but IMO it is moderately-sized at best.
I don't have anything really big that's convenient to check.

Tom