[Bug tree-optimization/107250] New: Load unnecessarily happens before malloc

["jmuizelaar at mozilla dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107250

            Bug ID: 107250
           Summary: Load unnecessarily happens before malloc
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jmuizelaar at mozilla dot com
  Target Milestone: ---

The following code will be compiled with the load of next happening before the
call to malloc. This generates worse code than if the load is delayed until
after the call to malloc.


struct Foo {
    Foo* next;
};
void ctx_push(Foo* f) {
    Foo tmp = { f->next };
    Foo *n = (Foo*)malloc(sizeof(Foo));
    *n = tmp;
    f->next = n;
}

Manually moving the load in this example improves the generated code:

struct Foo {
    Foo* next;
};

void ctx_push(Foo* f) {
    Foo *n = (Foo*)malloc(sizeof(Foo));
    Foo tmp = { f->next };
    *n = tmp;
    f->next = n;
}

https://gcc.godbolt.org/z/TnMj1c636