[Bug c++/50182] New: Performance degradation from gcc 4.1 (x86_64)

["oleg.smolsky at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50182

             Bug #: 50182
           Summary: Performance degradation from gcc 4.1 (x86_64)
    Classification: Unclassified
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: oleg.smolsky@gmail.com


G++ 4.6 emits slower code based on the following set of benchmarks:
    http://stlab.adobe.com/performance/ 

The discussion thread is here:
    http://gcc.gnu.org/ml/gcc/2011-07/threads.html#00506
    http://gcc.gnu.org/ml/gcc/2011-08/threads.html#00411

I digested one of the tests down to a single short case (see attachments):
    http://gcc.gnu.org/ml/gcc/2011-08/msg00391.html



g++ 4.1 (1.35 sec, 1185M ops/s):

.text:0000000000400FE0 loc_400FE0:
.text:0000000000400FE0                 movzx   eax, ds:data8[rdx]
.text:0000000000400FE7                 add     rdx, 1
.text:0000000000400FEB                 add     eax, 0Ah
.text:0000000000400FEE                 cmp     rdx, 1F40h
.text:0000000000400FF5                 lea     ecx, [rax+rcx]
.text:0000000000400FF8                 jnz     short loc_400FE0

g++ 4.6 (2.86s, 563M ops/s) :

.text:0000000000400D90 loc_400D90:
.text:0000000000400D90                 add     eax, 0Ah
.text:0000000000400D93                 add     al, [rdx]
.text:0000000000400D95                 add     rdx, 1
.text:0000000000400D99                 cmp     rdx, 503480h
.text:0000000000400DA0                 jnz     short loc_400D90

P.S. setting the component to C++. Optimizer?