https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63597
Bug ID: 63597
Summary: Generate useless trampoline for some nested function
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: patrick.pelissier at gmail dot com
In some cases, GCC generate a trampoline for nested functions whereas it is not
needed.
For example, for the code:
extern void h(void (*)(int*), int*);
int f(int x, int y) {
int a;
void g(int *ptr_a) {
*ptr_a = ptr_a[&x-&a] + ptr_a[&y-&a];
}
h(g, &a);
return a;
}
It generates a trampoline for function g:
movl $-17599, %eax
movl $-17847, %edx
movl %edi, 8(%rsp)
movl %esi, (%rsp)
leaq 12(%rsp), %rdi
leaq 4(%rsp), %rsi
movw %ax, 12(%rsp)
movl $g.1623, %eax
movl %eax, 2(%rdi)
movq %rsp, 8(%rdi)
movw %dx, 6(%rdi)
movl $-1864106167, 16(%rdi)
call h
whereas function g doesn't use this access and so doesn't need the trampoline:
g.1623:
.LFB1:
.cfi_startproc
movl -4(%rdi), %eax
addl 4(%rdi), %eax
movl %eax, (%rdi)
ret
(no use of %r10).
