Poor Performance gdc11 for base 64 with O3

[Mahdi]

In optimization level 3, gdc11 doesn't seem to work as well as  
gdc10 for base 64 benchmark.
On this site:
https://github.com/kostya/benchmarks#base64

, the poor performance of GDC 11 is well visible, but while 
version 10 did a good optimization.

I did a base 64 experiment on RISCV64 architecture  (other than 
Intel) with ubuntu-image:

In gdc-11(RISCV64):

      ubuntu at ubuntu:~/dlang/benchmark/benchmarks/base64/gdc-11$ 
gdc-11 -O3 test.d
      ubuntu at ubuntu:~/dlang/benchmark/benchmarks/base64/gdc-11$ 
time ./a.out
      encode aaaa... to YWFh...: 1431666688, 20.53
      decode YWFh... to aaaa...: 1073741824, 50.37

      real	1m11.219s
      user	1m10.793s
      sys	0m0.171s
     
______________________________________________________________________________
     In gdc-10(RISCv64):
      ubuntu at ubuntu:~/dlang/benchmark/benchmarks/base64/gdc-10$ 
gdc-10 -O3 test.d
      ubuntu at ubuntu:~/dlang/benchmark/benchmarks/base64/gdc-10$ 
time ./a.out
      encode aaaa... to YWFh...: 1431666688, 18.48
      decode YWFh... to aaaa...: 1073741824, 14.55

      real	0m33.447s
      user	0m33.108s
      sys	0m0.220s

source code from :
https://github.com/kostya/benchmarks/blob/master/base64/test.d