Hi, I've used your suggestion of "Specifying Registers for Local Variables" and found out that code it generates gives better results than my method. Unfortunately, a recent there on the subject: http://gcc.gnu.org/ml/gcc/2012-01/msg00305.html got me worried, so I would like to hear what you (or anyone familiar with the subjet) know about the status of implementation of "Local register Variables" in the AVR backend in gcc-4.5.3 and if it's better in newer gcc's. Specifically, I would like to know if you believe the following code is safe (assuming _mul16x16_32 is implemented correctly): DWord_t mul16x16_32(uint16_t x, uint16_t y)__attribute__((always_inline)); DWord_t mul16x16_32(uint16_t x, uint16_t y) { register uint16_t r24_25 asm ("r24") = x; register uint16_t r22_23 asm ("r22") = y; register uint16_t r30_31 asm ("r30"); register uint16_t r20_21 asm ("r20"); asm ( " call _mul16x16_32" "\n\t" : "=&r" (r20_21), "=&r" (r30_31) : "r" (r24_25), "r" (r22_23) : "r0", "r1", "cc" ); DWord_t Result; Result.High = r20_21; Result.Low = r30_31; return Result; } Thank, Ilya. On 10/24/11, Georg-Johann Lay <avr@xxxxxxxx> wrote: >> Hi, >> I'm doing some modifections to the avr backend to suit my needs. >> >> I would like to add new constrainst for individual registers to use in >> inline assembly blocks and i was wondering what is the correct way of >> doing this? > > Not on topic: You can have a look at GCC's "Specifying Registers for > Local Variables" feature: > http://gcc.gnu.org/onlinedocs/gcc/Local-Reg-Vars.html#Local-Reg-Vars > > For example, this enables you to interface non-ABI assembler functions > with C code without patching the compiler. > > Moreover, introducing individual register classes will result in a zoo > of constraints for 8-bit, 16-bit, 32-bit registers. > >> in gcc-4.5, i've added a new class for each register to reg_class, >> REG_CLASS_NAMES and REG_CLASS_CONTENTS, made a need constrainst for >> each register using its class and it worked as expected. >> >> i tried to do the same in gcc-4.7 and i got: >> internal compiler error: in find_costs_and_classes, at ira-costs.c:1704. > > You will have to debug the compiler proper. > > Notice that hooks like HARD_REGNO_MODE_OK put additional restrictions on > registers/mode combinations. > >> So i was wondering whether i did the wrong thing or just forgot to >> update some target hook. >> >> Thanks, >> Ilya. >
