Re: GCC inline assembler question


"Fred Nach" <fred_nach@xxxxxxxxxxx> schrieb im Newsbeitrag news:di0phu$qkl$1@xxxxxxxxxxxxxxxxxxxxxx 
Hi all !

I'm wondering how can i use "dummy registers" inside an inline assembly part ?
I mean, considering this code :

    asm("mov r1, %1, asr #15;"
"teq r1, %1, asr #31;"
"eorne %0, %1, %1, asr #31;"
:"=r" (output)
:"r" (input)
:"r1"
);

In this case, r1 is used only locally, and it is also clobbered, hence gcc will store its value (somewhere in the stack, memory, or other free register) before using it...
I would like to know how to let gcc determine the best register to use (for exemple if before that asm instrcution r6 is free... it leads to less store/load instructions).
Hard to explain but how can i specify to gcc that i want to use not specific register ... and let him decide the best to use ?

Thanks in advance for any help !!

Fred.

I've read some tutorial on gcc-asm dealing with this "problem". The suggestion was to "invent" additional output's - being the temporary registers - and assigning them to variables which are not used.

Raymund Hofmann 

.

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