https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78824
Bug ID: 78824
Summary: multiple add should in my opinion be optimized to
multiplication
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: pj at hugeone dot co.uk
Target Milestone: ---
Hi
Example (-O3)
volatile uint16_t y;
uint8_t nvx8;
int main(void) {
y = nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8
+ nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8;
}
translated to:
y = nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8
+ nvx8 + nvx8 + nvx8 + nvx8 + nvx8 + nvx8;
94: 80 91 00 01 lds r24, 0x0100
98: 28 2f mov r18, r24
9a: 30 e0 ldi r19, 0x00 ; 0
9c: c9 01 movw r24, r18
9e: 88 0f add r24, r24
a0: 99 1f adc r25, r25
a2: 88 0f add r24, r24
a4: 99 1f adc r25, r25
a6: 82 0f add r24, r18
a8: 93 1f adc r25, r19
aa: 82 0f add r24, r18
ac: 93 1f adc r25, r19
ae: 82 0f add r24, r18
b0: 93 1f adc r25, r19
b2: 82 0f add r24, r18
b4: 93 1f adc r25, r19
b6: 82 0f add r24, r18
b8: 93 1f adc r25, r19
ba: 82 0f add r24, r18
bc: 93 1f adc r25, r19
be: 82 0f add r24, r18
c0: 93 1f adc r25, r19
c2: 82 0f add r24, r18
c4: 93 1f adc r25, r19
c6: 82 0f add r24, r18
c8: 93 1f adc r25, r19
ca: 82 0f add r24, r18
cc: 93 1f adc r25, r19
ce: 82 0f add r24, r18
d0: 93 1f adc r25, r19
d2: 82 0f add r24, r18
d4: 93 1f adc r25, r19
d6: 90 93 02 01 sts 0x0102, r25
da: 80 93 01 01 sts 0x0101, r24
It should be optimized to multiplication I think.
