https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70784
Bug ID: 70784
Summary: Merge multiple short stores of immediates into wider
stores
Product: gcc
Version: unknown
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: ktkachov at gcc dot gnu.org
CC: ramana at gcc dot gnu.org
Target Milestone: ---
Consider the code:
struct bar {
int a;
char b;
char c;
char d;
char e;
char f;
char g;
}; // packed 64-bit structure
void
foozero (struct bar *p)
{
p->b = 0;
p->a = 0;
p->c = 0;
p->d = 0;
p->e = 0;
}
On aarch64 we currently generate:
foozero:
str wzr, [x0]
strb wzr, [x0, 4]
strb wzr, [x0, 5]
strb wzr, [x0, 6]
strb wzr, [x0, 7]
ret
But could generate a single 64-bit store:
foozero:
str xzr, [x0]
ret
Also, for:
void
foo (struct bar *p)
{
p->b = 0;
p->a = 0;
p->c = 0;
p->d = 1;
p->e = 0;
}
we could generate:
foo:
mov x1, #0x1000000000000
str x1, [x0]
Other targets could benefit from this too.
x86_64 currently generates for 'foo':
foo:
.LFB0:
.cfi_startproc
movl $0, (%rdi)
movb $0, 4(%rdi)
movb $0, 5(%rdi)
movb $1, 6(%rdi)
movb $0, 7(%rdi)
ret
but could genereate:
foo:
.LFB0:
.cfi_startproc
movabsq $281474976710656, %rax
movq %rax, (%rdi)
ret
