RFR: 8241042: x86_64: Improve Assembler generation

[Claes Redestad]

On 2020-03-16 18:51, Claes Redestad wrote:
>>>
>>> on x64, folding consecutive bytes emitted by Assembler routines into
>>> byte-wise variants of emit_int16, emit_int24 and emit_32 turns out to
>>> be profitable, since gcc can't seem to fold the back to back stores
>>> to the end() pointer into one. The new methods are also a bit
>>> convenient.
>>
>> Yes, I agree with this.
>>
>> Can you put () around arguments like next? It would be easy see them:
>>
>> emit_int24((0x44 | regenc), (scale << 6 | indexenc | baseenc), (disp & 
>> 0xFF));
> 
> Sure.
> 
>>
>> Or better put them on separate lines as you did in some cases.
> 
> I prefer keeping the expressions more compact, unless there's a need to
> comment on what's going on.
> 
>>
>> Can we avoid cast (unsigned char) or should we do it always (when sign 
>> bit may be set)? I seems we added it to avoid additional instructions 
>> generated by gcc. 

I've made a number of edits that should help with readability in places
where it got a bit muddied, especially in emit_operand:

http://cr.openjdk.java.net/~redestad/8241042/open.01/

Also made use of (unsigned char) a bit more consistent.

I think a follow up to examine if we can get rid of these casts by
changing arguments to uint8_t might be worthwhile.

Rerunning tier1+2.

/Claes