[Bug c++/54197] New: [4.7/4.8 regression] Lifetime of reference not properly extended

[ppluzhnikov at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54197

             Bug #: 54197
           Summary: [4.7/4.8 regression] Lifetime of reference not
                    properly extended
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: ppluzhni...@google.com


We've noticed this with 4.7 branch, confirmed present in current trunk (rev.
190209).

When calling a static member function returning an object (string below)
through an unnamed function pointer, and binding the result to a reference, the
lifetime of the returned temporary is not properly extended.

--- cut ---
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

struct string {
  string(const char *s) {
    s_ = strdup(s);
  }
  ~string() {
    memset((void*)s_, 'a', strlen(s_));
  }
  string(const string& rhs) {
    s_ = strdup(rhs.s_);
  }
  string& operator=(const string& rhs) {
    if (&rhs != this) {
      free((void*)s_);
      s_ = strdup(rhs.s_);
    }
    return *this;
  }
  const char *c_str() const { return s_; }

  const char *s_;
};

struct Foo {
  static string foo() { return "abcd"; }
};

Foo foo_g;

struct scoped_ptr {
  Foo* operator->() const { return &foo_g; }
  Foo* get() const { return &foo_g; }
};

Foo *get() { return &foo_g; }

int main()
{
  scoped_ptr f;
  const string& ref1 = f->foo();           // BAD
  const string& ref2 = f.get()->foo();     // BAD
  const string& ref3 = get()->foo();       // BAD
  const string& ref4 = Foo::foo();         // OK
  Foo *pf = f.get();
  const string& ref5 = pf->foo();          // OK


  printf("ref1: %p (%s)\n", ref1.c_str(), ref1.c_str());
  printf("ref2: %p (%s)\n", ref2.c_str(), ref2.c_str());
  printf("ref3: %p (%s)\n", ref3.c_str(), ref3.c_str());
  printf("ref4: %p (%s)\n", ref4.c_str(), ref4.c_str());
  printf("ref5: %p (%s)\n", ref5.c_str(), ref5.c_str());
}
--- cut ---

Result from gcc-4.6:

ref1: 0x5a8030 (abcd)
ref2: 0x5a8070 (abcd)
ref3: 0x5a80b0 (abcd)
ref4: 0x5a80d0 (abcd)
ref5: 0x5a80f0 (abcd)


Result from gcc-4.7 / 4.8

ref1: 0xe18010 (aaaa)  << BUG
ref2: 0xe18030 (aaaa)  << BUG
ref3: 0xe18050 (aaaa)  << BUG
ref4: 0xe18070 (abcd)
ref5: 0xe18090 (abcd)

Changing Foo::foo to be non-static (and commenting out ref4), the bug
disappears:

ref1: 0x1eb3010 (abcd)
ref2: 0x1eb3030 (abcd)
ref3: 0x1eb3050 (abcd)
ref5: 0x1eb3070 (abcd)


Google ref: b/6946758