2013/2/9 Grobman Alexander-R53196 <R53196@xxxxxxxxxxxxx>:
> "
> The valid set of registers for any argument are always expressed through constraints.
> "
>
> So if valid set is r5-r12 how do I express that?
>
> Alex.
>
Hi Grobman,
You need to design your customized reg_class, REG_CLASS_NAMES,
and REG_CLASS_CONTENTS. Also, you need to create new constraints
corresponding to the reg_class.
For your reference, here is my implementation for nds32 target:
(Sorry this target porting is not available yet on the GCC mainline.
But I am planning to contribute it into GCC 4.9 before stage 3.)
First, design our own valid register set, LOW_REGS, MIDDLE_REGS, and HIGH_REGS:
442 /* In nds32 target, we have three levels of registers:
443 LOW_COST_REGS : $r0 ~ $r7
444 MIDDLE_COST_REGS : $r8 ~ $r11, $r16 ~ $r19
445 HIGH_COST_REGS : $r12 ~ $r14, $r20 ~ $r31 */
446 enum reg_class
447 {
448 NO_REGS,
449 LOW_REGS,
450 MIDDLE_REGS,
451 HIGH_REGS,
... ...
457 GENERAL_REGS,
458 FRAME_REGS,
459 ALL_REGS,
460 LIM_REG_CLASSES
461 };
Second, design the strings corresponding to them:
465 #define REG_CLASS_NAMES \
466 { \
467 "NO_REGS", \
468 "LOW_REGS", \
469 "MIDDLE_REGS", \
470 "HIGH_REGS", \
... ...
476 "GENERAL_REGS", \
477 "FRAME_REGS", \
478 "ALL_REGS" \
479 }
Third, set the REG_CLASS_CONTENTS in bitwise fashion:
481 #define REG_CLASS_CONTENTS \
482 { \
483 {0x00000000, 0x00000000}, /* NO_REGS : */ \
484 {0x000000ff, 0x00000000}, /* LOW_REGS : 0-7 */ \
485 {0x000f0f00, 0x00000000}, /* MIDDLE_REGS : 8-11, 16-19 */ \
486 {0xfff07000, 0x00000000}, /* HIGH_REGS : 12-14, 20-31 */ \
... ...
492 {0xffffffff, 0x00000000}, /* GENERAL_REGS : 0-31 */ \
493 {0x00000000, 0x00000003}, /* FRAME_REGS : 32, 33 */ \
494 {0xffffffff, 0x00000003} /* ALL_REGS : 0-31, 32, 33 */ \
495 }
Finally, create new constraints corresponding to the reg_class:
28 (define_register_constraint "l" "LOW_REGS"
29 "Low cost registers $r0 ~ $r7")
30
31 (define_register_constraint "d" "MIDDLE_REGS"
32 "Middle cost registers $r8 ~ $r11, $r16 ~ $r19")
33
34 (define_register_constraint "h" "HIGH_REGS"
35 "High cost registers $r12 ~ $r14, $r20 ~ $r31")
36
After that, we can use 'l', 'd', or 'h' in the machine description.
Hope it helps ~ :)
Best regards,
jasonwucj
