https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82434
Bug ID: 82434
Summary: -fstore-merging does not work reliably.
Product: gcc
Version: 7.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: maxim.yegorushkin at gmail dot com
Target Milestone: ---
Consider the following code:
struct A
{
long a;
bool b, c, d, e;
};
struct B
{
long a;
bool b, c, d, e;
~B();
};
A f() {
A a;
a.a = 1;
a.b = true;
a.c = true;
a.d = true;
a.e = true;
return a;
}
B g() {
B b;
b.a = 1;
b.b = true;
b.c = true;
b.d = true;
b.e = true;
return b;
}
And the generated assembly:
f():
movl $1, %eax
movl $16843009, %edx
ret
g():
movq %rdi, %rax
movq $1, (%rdi)
movb $1, 8(%rdi)
movb $1, 9(%rdi)
movb $1, 10(%rdi)
movb $1, 11(%rdi)
ret
Declaring a destructor prevents returning an object of B in registers, which is
well documented.
Why isn't store merging applied in function g please?
