https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92549
Bug ID: 92549
Summary: Use x86 xchg instruction more
Product: gcc
Version: 9.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: drepper.fsp+rhbz at gmail dot com
Target Milestone: ---
Take this code
__attribute__((noinline))
int f(int a, int b)
{
return b - a + 5;
}
int foo(int a, int b)
{
return 1 + f(b, a);
}
int main()
{
return foo(39, 3);
}
gcc 9.2.1 generates for foo on x86-64 this code:
movl %edi, %r8d
movl %esi, %edi
movl %r8d, %esi
call f
addl $1, %eax
ret
This could be better:
xchgl %edi, %esi
call f
addl $1, %eax
ret
Switching parameter location is not a uncommon pattern.
If the regparm is used on x86-32 the same likely applies there.
