https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71344
Bug ID: 71344
Summary: [RL78] Really bad register allocation/utilization
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: olegendo at gcc dot gnu.org
Target Milestone: ---
Target: rl78-*-*
Compiling the following code for -mcpu=g10 -O2
char* test_00 (char* p)
{
int r = 0;
r |= p[0];
r |= p[1];
r |= p[2];
r |= p[-1];
p[3] = r;
return p + 3;
}
results in:
__Z7test_00Pc:
movw ax, [sp+4]
movw r8, ax
movw de, ax
movw hl, ax
mov a, [de]
or a, [hl+1]
mov r10, a
movw hl, r8
mov a, [hl+2]
or a, r10
mov r10, a
movw bc, r8
movw ax, r8
decw ax
movw hl, ax
mov a, [hl]
or a, r10
mov 3[bc], a
movw ax, r8
addw ax, #3
movw r8, ax
ret (total 39 bytes)
I think the minimal version would be:
movw ax,[sp+4]
movw hl,ax
mov a,[hl]
or a,[hl+1]
or a,[hl+2]
decw hl
or a,[hl]
mov [hl+4],a
movw ax,#3
addw ax,hl
movw r8,ax
ret (total 19 bytes)
