https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115733
Bug ID: 115733
Summary: [avr] Improve __memx address handling
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: gjl at gcc dot gnu.org
Target Milestone: ---
extern const __memx long vals4[];
extern const __memx char vals1[];
long load4_0 (void) { return vals4[0]; }
long load4_1 (void) { return vals4[1]; }
char load1_0 (void) { return vals1[0]; }
char load1_1 (void) { return vals1[1]; }
The code above uses PSImode addresses, which cannot be held in the Z register,
the register that has to be used in __memx accesses. Currently, non-REG
addresses are loaded to a reg, which causes additional copying. For example,
with v14 the function load4_0 compiles -Os -mmcu=atmega8 -d as:
load4_0:
ldi r24,lo8(vals4) ; 18 [c=4 l=3] *movpsi/4
ldi r25,hi8(vals4)
ldi r26,hlo8(vals4)
movw r30,r24 ; 19 [c=4 l=1] *movhi/0
mov r21,r26 ; 20 [c=4 l=1] movqi_insn/0
rcall __xload_4 ; 21 [c=16 l=1] *xload_si_libgcc
/* epilogue start */
ret ; 24 [c=0 l=1] return
Symbol "vals4" is first loaded to PSI:24, and the the lo16 part is copied to Z
and the hlo8 part to elsewhere. The code could be like:
load4_0:
ldi r30,lo8(vals4) ; 13 [c=4 l=2] *set_z_lo16
ldi r31,hi8(vals4)
ldi r21,hh8(vals4) ; 15 [c=4 l=1] *set_reg_hh8
rcall __xload_4 ; 19 [c=16 l=1] *xload_si_libgcc
/* epilogue start */
ret ; 22 [c=0 l=1] return
