[PATCH] S/390: HW accelerated iconv module for iso-8859-1/cp37 conversions

[Florian Weimer]

On 10/13/2015 02:17 PM, Andreas Krebbel wrote:
> On 10/13/2015 02:07 PM, Florian Weimer wrote:
>> On 10/13/2015 01:50 PM, Andreas Krebbel wrote:
>>> On 10/13/2015 12:40 PM, Andreas Schwab wrote:
>>>> "Andreas Krebbel" <krebbel@linux.vnet.ibm.com> writes:
>>>>
>>>>> +    asm volatile ("0:                        \n\t"			\
>>>>> +                  "  troo    %0,%1           \n\t"			\
>>>>> +                  "  jz      1f              \n\t"			\
>>>>> +                  "  jo      0b              \n\t"			\
>>>>> +                  "  llgc    %3,0(%1)        \n\t"			\
>>>>> +                  "  la      %3,0(%3,%4)     \n\t"			\
>>>>> +                  "  mvc     0(1,%0),0(%3)   \n\t"			\
>>>>> +                  "  aghi    %1,1            \n\t"			\
>>>>> +                  "  aghi    %0,1            \n\t"			\
>>>>> +                  "  aghi    %2,-1           \n\t"			\
>>>>> +                  "  j       0b              \n\t"			\
>>>>> +                  "1:                        \n"			\
>>>>> +									\
>>>>> +     : "+a" (pOutput), "+a" (pInput), "+d" (length), "=&a" (tmp)        \
>>>>
>>>> That doesn't force %1 to be an even numbered register.
>>>>
>>>> ../iconv/loop.c: Assembler messages:
>>>> ../iconv/loop.c:326: Fatal error: odd numbered general purpose register specified as register pair
>>>
>>> Only %0 is required to be a register pair. This is enforced with the register asm definition above:
>>>
>>> register unsigned char *pOutput asm ("2") = outptr;
>>>
>>> So it looks like GCC is not respecting the register asm in your case?!
>>
>> GCC can make a copy of the register variable before passing it to the
>> asm statement.  The “+” in the constraint probably encourages that.
> 
> No. GCC guarantees that it will use the register specified with register __asm__ as operand for
> inline assemblies.  Please see: https://gcc.gnu.org/onlinedocs/gcc/Local-Reg-Vars.html#Local-Reg-Vars
> 
> "... However, using the variable as an input or output operand to the asm guarantees that the
> specified register is used for that operand. See Extended Asm, for more information. ..."

Interesting.  I still suspect that somehow “+” breaks this guarantee.

Andreas, can you provide the .S file from your GCC version (and perhaps
RTL dumps)?

Florian