PATCH: PR target/39911: The 'z' suffix doesn't work with 16bit integer insn

[Uros Bizjak]

H.J. Lu wrote:

>>>> In fact, operand modifiers are not documented at all except ia64 `%Pn'.
>>>>         
>>> I saw
>>>
>>>   `m'
>>>           Memory operand.  Remember that `m' allows postincrement and
>>>           postdecrement which require printing with `%Pn' on IA-64.
>>>           Use `S' to disallow postincrement and postdecrement.
>>>
>>> Can you tell how to use it from above? I have to find an example for it.
>>> Guess where I can find such examples?
>>>       
>> I see your point, but if one looks for %z in config/i386/i386.md he gets
>>
>> ;; 'z' mov%z1 would be movl, movw, or movb depending on the mode of
>> ;;     operands[1].
>>
>> which is exactly the definition that Uros is pushing.
>>     
>
> There are several problems:
>
> 1. It is still the part of gcc source. It isn't the user documentation.
> Given some out-of-date comments and actual usages in gcc source,
> I will take actual usages over some out-of-date comments.
> 2. %z is fully implemented and used for x87 insns.
> 3. "movq" isn't mentioned.
> 4. "movw/movq" never worked on memory operand.
>   

My reasoning for fixing "%z" are:
- users found %z in the comment from i386.md and used it exactly in the 
way as shown there.
- %z with x87 doesn not give the suffix as mentioned in the comment above.
- there were separate bugreports for ICEs in print_operand with QImode 
operands and DImode operands. There were reports for wrong HImode suffix 
for memory operands as well as DImode memory operands. Actually, 
everything that could go wrong went wrong and these bugreports shows the 
pattern of uses for %z - also for DImode, even if "movq" is not mentioned.

Users are expecting %z to give "q,l,w,b" consistently for register and 
memory operands. Regarding x87, not even glibc took the opportunity to 
use fistp%z in mathinline.h [1].

The decision to "break" (?) existing code for x87 was done on these 
usage patterns. %z modifier was always PITA, so let's give users what 
they want and let's document the correct usage. And that is %z for all 
integer and %Z for FP insns.

[1] 
http://sourceware.org/cgi-bin/cvsweb.cgi/libc/sysdeps/i386/fpu/bits/mathinline.h?rev=1.62&content-type=text/x-cvsweb-markup&cvsroot=glibc

Uros.