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From: "marco at technoboredom dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/45115]  New: attribute((pure)) does not work when returning structs
Date: Wed, 28 Jul 2010 19:45:00 -0000	[thread overview]
Message-ID: <bug-45115-3116@http.gcc.gnu.org/bugzilla/> (raw)

compiling this with 'gcc -O3 -S x.c'

-------- x.c -----------
#define PURE __attribute__((pure))

struct res {int u; };
extern struct res calc_1() PURE; 
extern int        calc_2() PURE;

int fun_1() 
{
        return calc_1().u+calc_1().u;
}
int fun_2() 
{
        return calc_2()+calc_2();
}
--------------------

yields code which calls calc_2() *once* in fun_2() but calls calc_1() *twice*
in fun_1(). Obviously, fun_1 misses an optimization.

Tested on gcc 4.4.3 (Ubuntu 10.04), gcc 4.5.0/4.4.4/4.3.5 (MacPorts)


-- 
           Summary: attribute((pure)) does not work when returning structs
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: marco at technoboredom dot net
  GCC host triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45115


             reply	other threads:[~2010-07-28 19:45 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-07-28 19:45 marco at technoboredom dot net [this message]
2010-07-28 19:48 ` [Bug tree-optimization/45115] pure functions returning structs are not optimized pinskia at gcc dot gnu dot org
2010-07-28 20:05 ` rguenth at gcc dot gnu dot org

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