https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120692
Bug ID: 120692
Summary: Copying of adjacent fields can be merged
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hiraditya at msn dot com
Target Milestone: ---
Saw this on X(https://x.com/joseph_h_garvin/status/1934705584705843340)
Assigning adjacent field of struct can be merged as a copy but clang does not
recognize it when the data types are different.
Repro:
```cpp
#include <functional>
struct handle {
void* data; // Replacing it with int data works.
int index;
};
void remove(handle* p, int idx, int& end)
{
auto& item = p[idx];
auto& last = p[end];
item = last;
--end;
}
void remove2(handle* p, int idx, int& end)
{
auto& item = p[idx];
auto& last = p[end];
item.data = last.data;
item.index = last.index;
--end;
}
```
$ clang -O2
```asm
remove(handle*, int, int&):
ldrsw x8, [x2]
ldr q0, [x0, x8, lsl #4]
str q0, [x0, w1, sxtw #4]
ldr w8, [x2]
sub w8, w8, #1
str w8, [x2]
ret
remove2(handle*, int, int&):
ldrsw x8, [x2]
add x9, x0, w1, sxtw #4
add x8, x0, x8, lsl #4
ldr w10, [x8, #8]
ldr x8, [x8]
str w10, [x9, #8]
ldr w10, [x2]
str x8, [x9]
sub w8, w10, #1
str w8, [x2]
ret
```
https://godbolt.org/z/61avd145T
