Struct rvals are dereferenced too many times

[jyn514]

Describe the bug
Structs are dereferenced one too many times

Expected behavior
A struct deref (get_struct()->m) performs one deref.

Actual Behavior
Struct derefs perform two derefs.

Code

$ cargo run
typedef unsigned int __uid_t;
extern __uid_t getuid (void) ;

struct passwd {
  char *pw_name;
  char *pw_passwd;
};

extern struct passwd *getpwuid (__uid_t __uid);
extern int puts (const char *__s);

int main(void) {
  puts(getpwuid(getuid())->pw_name);
}
$ ./a.out
Segmentation fault

AST

Please paste the output of cargo run -- --debug-ast here.

typedef unsigned int __uid_t;
extern __uid_t getuid (void) ;

struct passwd {
  char *pw_name;
  char *pw_passwd;
};

extern struct passwd *getpwuid (__uid_t __uid);
extern int puts (const char *__s);

int main(void) {
  puts(getpwuid(getuid())->pw_name);
}
extern unsigned int getuid(void);
extern unsigned int getuid(void);
extern struct passwd * getpwuid(unsigned int);
extern struct passwd * getpwuid(unsigned int);
extern int puts(char *);
auto int main(void) {
(puts)(*((*((getpwuid)((getuid)()))).pw_name));
}

ASM

function u0:0() -> i32 system_v {
    sig0 = () -> i32 system_v
    sig1 = (i32) -> i64 system_v
    sig2 = (i64) -> i32 system_v
    fn0 = u0:0 sig0
    fn1 = u0:1 sig1
    fn2 = u0:2 sig2

ebb0:
    v0 = call fn0()
    v1 = call fn1(v0)
    v2 = load.i64 v1
    v3 = iconst.i64 0
    v4 = iadd v2, v3
    v5 = load.i64 v4
    v6 = call fn2(v5)
    v7 = iconst.i32 0
    return v7
}

[jyn514]

This can be worked around by putting the struct assignment on its own line:

struct passwd *p = getpwuid(getuid());
puts(p->pw_name);

Maybe our code assumes that structs are always stored in a variable?