https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95014
Bug ID: 95014
Summary: gcc fails to merge two identical returns
Product: gcc
Version: 10.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: rafael at espindo dot la
Target Milestone: ---
Given
#include <new>
union any {
any(any&& x) noexcept {
if (x.st < 4) {
st = x.st;
x.st = 0;
} else {
ex = x.ex;
x.ex = nullptr;
}
}
long st;
void* ex;
};
void f(any* a, any* b) {
new (a) any(std::move(*b));
}
gcc produces
movq (%rsi), %rax
movq %rax, (%rdi)
movq $0, (%rsi)
cmpq $3, %rax
jg .L2
ret
.L2:
ret
clang produces
movq (%rsi), %rax
cmpq $3, %rax
movq %rax, (%rdi)
movq $0, (%rsi)
retq
So clang has a redundant cmpq and gcc has the cmpq and two identical branch
destinations.
