[no subject]

typedef unsigned long long u64;
union ktime
{
  s64 tv64;
};
typedef union ktime ktime_t;
ktime_t ns_to_ktime (u64 ns);
union ktime const ktime_zero = { 0LL };

ktime_t
ns_to_ktime (u64 ns)
{
  ktime_t __constr_expr_0;

  {
    __constr_expr_0.tv64 = (s64) ((u64) ktime_zero.tv64 + ns);
    return (__constr_expr_0);
  }
}

/* Checksum = 1A82CF6 */

this generates with 4.5.0 20091219 -O2 

 movq    %rdi, %rax
 addq    ktime_zero(%rip), %rax
 ret

llvm in this case uses the known const value of ktime_zero and just generates
an assignment (this makes more difference with -m32) gcc should too.


-- 
           Summary: missing constant evaluation for const union
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: andi-gcc at firstfloor dot org
  GCC host triplet: x86_64-linux
GCC target triplet: x86-64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42591

>From 
Received: (qmail 12960 invoked by uid 48); 3 Jan 2010 07:14:00 -0000
Date: 3 Jan 2010 07:14:00 -0000
Subject: [Bug tree-optimization/42591]  New: missing constant evaluation for const union
X-Bugzilla-Reason: CC
Message-ID: <bug-42591-7834@http.gcc.gnu.org/bugzilla/>
Reply-To: gcc-bugzilla@gcc.gnu.org
To: gcc-bugs@gcc.gnu.org
From: "andi-gcc at firstfloor dot org" <gcc-bugzilla@gcc.gnu.org>

typedef long long s64;