https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81147
--- Comment #8 from Felipe Magno de Almeida <felipe at expertisesolutions dot
com.br> ---
With GCC 7.2.0 I'm still not seeing the same results as you are. The following
is the assembly result, using the same .cpp file and the same command line:
.section .text._Z3abcv,"ax",@progbits
.global _Z3abcv
.type _Z3abcv, @function
_Z3abcv:
push r28 ; ; 52 pushqi1/1 [length = 1]
push r29 ; ; 53 pushqi1/1 [length = 1]
in r28,__SP_L__ ; ; 54 *movhi/8 [length = 2]
in r29,__SP_H__ ;
sbiw r28,15 ; , ; 55 *addhi3/3 [length = 1]
in __tmp_reg__,__SREG__ ; 56 movhi_sp_r/3 [length = 5]
cli
out __SP_H__,r29 ; ,
out __SREG__,__tmp_reg__
out __SP_L__,r28 ; ,
/* prologue: function */
/* frame size = 15 */
/* stack size = 17 */
.L__stack_usage = 17
ldi r24,lo8(32) ; D.1843, ; 6 movqi_insn/2 [length = 1]
; test.cpp:19: seq(L l, R r) : l(l), r(r) {}
std Y+7,__zero_reg__ ; D.2011.l, ; 37 movqi_insn/3 [length
= 1]
ldi r25,lo8(97) ; D.1843, ; 42 movqi_insn/2 [length = 1]
std Y+8,r25 ; D.2011.l, D.1843 ; 38 movqi_insn/3 [length
= 1]
std Y+9,r24 ; D.2011.l, D.1843 ; 39 movqi_insn/3 [length
= 1]
; test.cpp:25: return { l, r};
std Y+10,r24 ; MEM[(struct seq *)&D.2011 + 4B], D.1843 ; 14
movqi_insn/3 [length = 1]
ldi r24,lo8(5) ; tmp47, ; 15 movqi_insn/2 [length = 1]
movw r30,r28 ; , ; 45 *movhi/1 [length = 1]
adiw r30,6 ; , ; 16 *addhi3/3 [length = 1]
movw r26,r28 ; , ; 46 *movhi/1 [length = 1]
adiw r26,1 ; , ; 17 *addhi3/3 [length = 1]
0: ; 18 movmem_qi [length = 4]
ld r0,Z+ ;
st X+,r0 ;
dec r24 ; tmp47
brne 0b
ldi r24,lo8(5) ; tmp48, ; 19 movqi_insn/2 [length = 1]
movw r30,r28 ; , ; 47 *movhi/1 [length = 1]
adiw r30,1 ; , ; 20 *addhi3/3 [length = 1]
movw r26,r28 ; , ; 48 *movhi/1 [length = 1]
adiw r26,6 ; , ; 21 *addhi3/3 [length = 1]
0: ; 22 movmem_qi [length = 4]
ld r0,Z+ ;
st X+,r0 ;
dec r24 ; tmp48
brne 0b
; test.cpp:35: )
ldi r24,lo8(5) ; tmp49, ; 23 movqi_insn/2 [length = 1]
movw r30,r28 ; , ; 49 *movhi/1 [length = 1]
adiw r30,6 ; , ; 24 *addhi3/3 [length = 1]
movw r26,r28 ; , ; 50 *movhi/1 [length = 1]
adiw r26,11 ; , ; 25 *addhi3/3 [length = 1]
0: ; 26 movmem_qi [length = 4]
ld r0,Z+ ;
st X+,r0 ;
dec r24 ; tmp49
brne 0b
; test.cpp:37: foo(rule);
movw r24,r28 ; , ; 51 *movhi/1 [length = 1]
adiw r24,11 ; , ; 28 addhi3_clobber/1 [length = 1]
call _Z3fooI3seqIS0_I1AS1_ES1_EEvRT_ ; ; 29 call_insn/2
[length = 2]
/* epilogue start */
; test.cpp:38: }
adiw r28,15 ; , ; 59 *addhi3/3 [length = 1]
in __tmp_reg__,__SREG__ ; 60 movhi_sp_r/3 [length = 5]
cli
out __SP_H__,r29 ; ,
out __SREG__,__tmp_reg__
out __SP_L__,r28 ; ,
pop r29 ; ; 61 popqi [length = 1]
pop r28 ; ; 62 popqi [length = 1]
ret ; 63 return_from_epilogue [length = 1]
.size _Z3abcv, .-_Z3abcv
.ident "GCC: (GNU) 7.2.0"
And this is the result if seq no longer inherits from seq_base (which is an
empty class):
.section .text._Z3abcv,"ax",@progbits
.global _Z3abcv
.type _Z3abcv, @function
_Z3abcv:
push r28 ; ; 19 pushqi1/1 [length = 1]
push r29 ; ; 20 pushqi1/1 [length = 1]
; SP -= 3 ; ; 24 *addhi3_sp [length = 1]
rcall .
in r28,__SP_L__ ; ; 25 *movhi/8 [length = 2]
in r29,__SP_H__ ;
/* prologue: function */
/* frame size = 3 */
/* stack size = 5 */
.L__stack_usage = 5
; test.cpp:35: )
ldi r24,lo8(97) ; tmp42, ; 5 movqi_insn/2 [length = 1]
std Y+1,r24 ; MEM[(struct seq *)&rule], tmp42 ; 6
movqi_insn/3 [length = 1]
ldi r24,lo8(32) ; tmp43, ; 7 movqi_insn/2 [length = 1]
std Y+2,r24 ; MEM[(struct seq *)&rule + 1B], tmp43 ; 8
movqi_insn/3 [length = 1]
std Y+3,r24 ; MEM[(struct seq *)&rule + 2B], tmp43 ; 10
movqi_insn/3 [length = 1]
; test.cpp:37: foo(rule);
movw r24,r28 ; , ; 18 *movhi/1 [length = 1]
adiw r24,1 ; , ; 11 *addhi3/3 [length = 1]
call _Z3fooI3seqIS0_I1AS1_ES1_EEvRT_ ; ; 12 call_insn/2
[length = 2]
/* epilogue start */
; test.cpp:38: }
; SP += 3 ; ; 30 *addhi3_sp [length = 3]
pop __tmp_reg__
pop __tmp_reg__
pop __tmp_reg__
pop r29 ; ; 31 popqi [length = 1]
pop r28 ; ; 32 popqi [length = 1]
ret ; 33 return_from_epilogue [length = 1]
.size _Z3abcv, .-_Z3abcv
.ident "GCC: (GNU) 7.2.0"
Which seems to indicate that in avr backend, when a class inherits from another
(be that trivial or not), named return value optimization no longer kicks in
and all return types gets copied.
