On 8/30/20 2:30 PM, Taylor Simpson wrote:
>
>
>> -----Original Message-----
>> From: Richard Henderson <richard.hender...@linaro.org>
>> Sent: Sunday, August 30, 2020 3:13 PM
>> To: Taylor Simpson <tsimp...@quicinc.com>; qemu-devel@nongnu.org
>> Cc: phi...@redhat.com; laur...@vivier.eu; riku.voi...@iki.fi;
>> aleksandar.m.m...@gmail.com; a...@rev.ng
>> Subject: Re: [RFC PATCH v3 30/34] Hexagon (target/hexagon) TCG for
>> instructions with multiple definitions
>>
>> On 8/30/20 12:48 PM, Taylor Simpson wrote:
>>> I'll add the following comment to indicate what's going on
>>>
>>> /*
>>> * Each of the generated helpers is wrapped with #ifndef
>> fGEN_TCG_<tag>.
>>> * For example
>>> * #ifndef fGEN_TCG_A2_add
>>> * DEF_HELPER_3(A2_add, s32, env, s32, s32)
>>> * #endif
>>> * We include gen_tcg.h here to provide definitions of fGEN_TCG for any
>> instructions that
>>> * are overridden.
>>> *
>>> * This prevents unused helpers from taking up space in the executable.
>>> */
>>
>> Ah, hum. Well.
>>
>> How about we figure out a way to communicate to the generator scripts
>> which
>> functions have been implemented "directly", and don't need to be
>> generated at all?
>>
>> I don't see why we have to wait until the c preprocessor to remove this
>> unused
>> code, and the less we have of it, the better.
>>
>
> A few reasons
> - Makes it easy to override instruction helpers. All one has to do is
> #define fGEN_TCG_<tag>.
If the generator can examine, say, genptr_override.c.inc, then you don't even
have to add a #define. Just add the code.
Perhaps something like
DEFINE_FGEN(tag)
{
// some code
}
where DEFINE_FGEN expands to the appropriate function declaration. The
generator then need only grep '^DEFINE_FGEN' and extract the list of overridden
tags.
> - When debugging the override, sometimes you want to quickly revert back to
> the helper. Or if you've written a bunch of overrides in one shot and then
> find that a test case is failing, you can binary search which one to turn off
> and get the test to pass. This is the one with the bug to fix.
No difference there, just binary searching on different text.
> - Reduces time for an incremental build. When we add or delete an override,
> we don't have to re-run the generator.
About this I care not at all. I can't imagine that more than fractions of a
second are at stake.
r~
