Fwd: Regardig asm volatile query

Fwd: Regardig asm volatile query

[paladin tripathi]

Hi All,

asm volatile (
 "\n\t"
:
: "r" (pu8In4), "r" (s32PosInt), "r" (s16CoeffOrg), "r" (u32PosFrac),
"r" (u8Out), "r" (u32Step), "r" (u32TgtWidth)
: "r2", "r3", "r4", "r5", "r6", "r7", "r8
 );

I have tested the above application with gcc-4.3 and  gcc-4.2 toolchain:-
With gcc-4.2 we are able to compile the aboe code with –O1
#gcc-4.2 reg_org.c -O1

but getting the following error while compiling the code with gcc-4.3
#gcc-4.3 reg_org.c -O1
reg_org.c:12: error: can't find a register in class 'GENERAL_REGS'
while reloading 'asm'
reg_org.c:12: error: 'asm' operand has impossible constraints

I Want to know
1-> why compilation is happening with gcc-4.2 toolchian not with gcc-4.3
2-> what is the difference between gcc-4.2 and gcc4.3 related to asm volatile


Thanks,

Re: Regardig asm volatile query

[Segher Boessenkool]

> asm volatile (
>  "\n\t"
> :
> : "r" (pu8In4), "r" (s32PosInt), "r" (s16CoeffOrg), "r" (u32PosFrac),
> "r" (u8Out), "r" (u32Step), "r" (u32TgtWidth)
> : "r2", "r3", "r4", "r5", "r6", "r7", "r8
>  );

You have 7 inputs and 7 clobbers.  Assuming this is ARM or some other
arch with about 16 regs, this is very much pushing the boundaries of
the possible.

> reg_org.c:12: error: can't find a register in class 'GENERAL_REGS'
> while reloading 'asm'
> reg_org.c:12: error: 'asm' operand has impossible constraints
>
> I Want to know
> 1-> why compilation is happening with gcc-4.2 toolchian not with  
> gcc-4.3

You got lucky with 4.2, and you don't with 4.3 .

> 2-> what is the difference between gcc-4.2 and gcc4.3 related to  
> asm volatile

Nothing really.  The compiler sometimes needs a few registers to do  
other
things, but you used up all of them.


Segher

Re: Regardig asm volatile query

[Andrew Haley]

On 07/29/2010 02:35 PM, Segher Boessenkool wrote:
>> asm volatile (
>>  "\n\t"
>> :
>> : "r" (pu8In4), "r" (s32PosInt), "r" (s16CoeffOrg), "r" (u32PosFrac),
>> "r" (u8Out), "r" (u32Step), "r" (u32TgtWidth)
>> : "r2", "r3", "r4", "r5", "r6", "r7", "r8
>>  );
> 
> You have 7 inputs and 7 clobbers.  Assuming this is ARM or some other
> arch with about 16 regs, this is very much pushing the boundaries of
> the possible.
> 
>> reg_org.c:12: error: can't find a register in class 'GENERAL_REGS'
>> while reloading 'asm'
>> reg_org.c:12: error: 'asm' operand has impossible constraints
>>
>> I Want to know
>> 1-> why compilation is happening with gcc-4.2 toolchian not with gcc-4.3
> 
> You got lucky with 4.2, and you don't with 4.3 .
> 
>> 2-> what is the difference between gcc-4.2 and gcc4.3 related to asm
>> volatile
> 
> Nothing really.  The compiler sometimes needs a few registers to do other
> things, but you used up all of them.

That's right.  If you look a bit more you will see that this is the same
question as http://gcc.gnu.org/ml/gcc-help/2010-07/msg00046.html
which I answered in the same way, but was ignored.

Perhaps they'll keep asking until they get an answer they like.

Andrew.