https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119424
Bug ID: 119424
Summary: memcpy->memset optimization should happen even for
non-constant form of memcpy
Product: gcc
Version: 14.1.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: pinskia at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Take:
```
void g(int*,int s);
void f(int s)
{
//s = 222;
int buffer[222]={};
int buffer1[222];
__builtin_memcpy(&buffer1[0], &buffer[0], s*sizeof(int));
g(buffer1,s);
}
void f1(int s)
{
//s = 222;
int buffer[222]={};
int buffer1[222];
__builtin_memset(&buffer1[0], 0, s*sizeof(int));
g(buffer1,s);
}
```
We should be able to transform f to f1 but we current does not. If s was
constant, we could do it. In this case if s was `>= 222`, then it would be
undefined behavior so doing it always seems like a good idea.
This alone won't solve the testcase in PR 103483 but it might improve other
cases.
