GCC rychle kopirovani pameti

[Jaroslav Buchta]

Resenim je dat fci fastcopy do jineho modulu ale stejne by me zajimalo, 
jestli to je normalni.

Dne 08.06.2018 v 12:01 Jaroslav Buchta napsal(a):
> Zdravim, dnes se zase nestiham divit, nevim, na cem je to jak zavisle 
> ale bezna funkce memcpy vede jak v optimalizovanem tak v 
> neoptimalizovanem prekladu k hloupemu kopirovani po 1B
>
> Zkusil jsem si napsat takovouto fci
>
> void fastcpy(void *dst, void *src, int len)
> {
>     while (len >= 8)
>     {
>         *(uint64_t*)dst = *(uint64_t*)src;
>         dst += 8;
>         src += 8;
>         len -= 8;
>     }
>     while (len >= 4)
>     {
>         *(uint32_t*)dst = *(uint32_t*)src;
>         dst += 4;
>         src += 4;
>         len -= 4;
>     }
>     if (len >= 2)
>     {
>         *(uint16_t*)dst = *(uint16_t*)src;
>         dst += 2;
>         src += 2;
>         len -= 2;
>     }
>     if (len != 0)
>     {
>         *(uint8_t*)dst = *(uint8_t*)src;
>     }
> }
>
> ktera vede ke kyzenemu vysledku, je to vyrazne rychlejsi, ovsem POUZE, 
> KDYZ NENI NASTAVENA OPTIMALIZACE O3, tam nejak prekladac usoudi, ze je 
> to kopirovani bloku a vola memcpy... Je to vubec mozne, nebo delam 
> nejakou chybu???
>
> Jak mam vynutit volani te funkce? (krome obchuzky, ze pro ni zakazu 
> optimalizaci...)
>
>
> ////////////////////////////////
>
> Optimalizovany kod:
>
> 100               mccState.iB = (float)(mccState.bufAdc1[2]);
> 080004c2:   vstr    s14, [r4, #68]  ; 0x44
> 080004c6:   vstr    s15, [r4, #72]  ; 0x48
> 102               if (!mccStateCopy.f_LockCopy)
> 080004ca:   bmi.n   0x8000400 <HAL_ADC_ConvCpltCallback+24>
> 080004cc:   movs    r2, #72 ; 0x48
> 080004ce:   mov     r1, r4
> 080004d0:   add.w   r0, r4, #76     ; 0x4c
> 080004d4:   bl      0x8005e00 <memcpy>
>  72               *(uint32_t*)dst = *(uint32_t*)src;
>
>
> Neoptimalizovany kod:
>
> 101               mccState.iC = (float)(mccState.bufAdc1[3]);
> 08000528:   vmov    s15, r1
> 0800052c:   vcvt.f32.u32    s15, s15
> 08000530:   vstr    s15, [r3, #72]  ; 0x48
> 102               if (!mccStateCopy.f_LockCopy)
> 08000534:   ldrb.w  r3, [r3, #76]   ; 0x4c
> 08000538:   tst.w   r3, #2
> 0800053c:   bne.n   0x8000470 <HAL_ADC_ConvCpltCallback+24>
> 104                   fastcpy((void *)&mccStateCopy, (void 
> *)&mccState, sizeof(MCCOMSTATE));
> 0800053e:   ldr     r0, [pc, #16]   ; (0x8000550 
> <HAL_ADC_ConvCpltCallback+248>)
> 08000540:   movs    r2, #76 ; 0x4c
> 08000542:   mov     r1, r0
> 08000544:   add     r0, r2
> 08000546:   bl      0x80003f4 <fastcpy>
>
>
>           fastcpy:
> 080003f4:   cmp     r2, #7
> 080003f6:   ble.n   0x800043a <fastcpy+70>
>  62       {
> 080003f8:   push    {r4, r5}
>  65               *(uint64_t*)dst = *(uint64_t*)src;
> 080003fa:   ldrd    r4, r5, [r1], #8
> 080003fe:   strd    r4, r5, [r0], #8
>  68               len -= 8;
> 08000402:   subs    r2, #8
>  63           while (len >= 8)
> 08000404:   cmp     r2, #7
> 08000406:   bgt.n   0x80003fa <fastcpy+6>
> 08000408:   b.n     0x8000414 <fastcpy+32>
>  72               *(uint32_t*)dst = *(uint32_t*)src;
> 0800040a:   ldr.w   r3, [r1], #4
> 0800040e:   str.w   r3, [r0], #4
>  75               len -= 4;
> 08000412:   subs    r2, #4
>  70           while (len >= 4)
> 08000414:   cmp     r2, #3
> 08000416:   bgt.n   0x800040a <fastcpy+22>
>  77           if (len >= 2)
> 08000418:   cmp     r2, #1
> 0800041a:   ble.n   0x8000426 <fastcpy+50>
>  79               *(uint16_t*)dst = *(uint16_t*)src;
> 0800041c:   ldrh.w  r3, [r1], #2
> 08000420:   strh.w  r3, [r0], #2
>  82               len -= 2;
> 08000424:   subs    r2, #2
>  84           if (len != 0)
> 08000426:   cbz     r2, 0x800042c <fastcpy+56>
>  86               *(uint8_t*)dst = *(uint8_t*)src;
> 08000428:   ldrb    r3, [r1, #0]
> 0800042a:   strb    r3, [r0, #0]
>  88       }
> 0800042c:   pop     {r4, r5}
> 0800042e:   bx      lr
> 08000430:   ldr.w   r3, [r1], #4
> 08000434:   str.w   r3, [r0], #4
>  75               len -= 4;
> 08000438:   subs    r2, #4
> 0800043a:   cmp     r2, #3
> 0800043c:   bgt.n   0x8000430 <fastcpy+60>
> 0800043e:   cmp     r2, #1
> 08000440:   ble.n   0x800044c <fastcpy+88>
> 08000442:   ldrh.w  r3, [r1], #2
> 08000446:   strh.w  r3, [r0], #2
>  82               len -= 2;
> 0800044a:   subs    r2, #2
>  84           if (len != 0)
> 0800044c:   cmp     r2, #0
> 0800044e:   beq.n   0x800042e <fastcpy+58>
>  86               *(uint8_t*)dst = *(uint8_t*)src;
> 08000450:   ldrb    r3, [r1, #0]
> 08000452:   strb    r3, [r0, #0]
> 08000454:   bx      lr
>
>
>
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