https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104316
Bug ID: 104316
Summary: Missing optimization for uninitialized local struct
variable
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: roland.illig at gmx dot de
Target Milestone: ---
~~~c
#include <stdlib.h>
typedef struct Buffer {
char *buf;
size_t len;
size_t cap;
} Buffer;
Buffer Buffer_Init_Return(void);
void Buffer_Init_Ref(Buffer *buf);
void Buffer_Add(Buffer *buf, const char *);
void
Use_Buffers(void)
{
Buffer buf1 = Buffer_Init_Return();
Buffer buf2;
buf2 = Buffer_Init_Return();
Buffer_Add(&buf1, "1");
Buffer_Add(&buf2, "2");
}
~~~
https://godbolt.org/z/qTz36qP9r
The code snippets for initializing buf1 and buf2 are almost the same. From an
as-if perspective, they are identical.
GCC 12 generates several copy instructions when initializing buf2, while Clang
and ICC generate the straight-forward code.
Would it be difficult to tell GCC to optimize the above initialization for
buf2, for the case that buf2 is not accessed between the declaration and the
assignment?
