On Thu, 29 Jun 2017, zhong jiang wrote: > On 2017/6/29 6:13, Thomas Gleixner wrote: > > That's simply wrong. If oparg is negative and the SHIFT bit is set then the > > result is undefined today and there is no way that this can be used at > > all. > > > > On x86: > > > > 1 << -1 = 0x80000000 > > 1 << -2048 = 0x00000001 > > 1 << -2047 = 0x00000002 > but I test the cases in x86_64 all is zero. I wonder whether it is related to gcc or not > > zj.c:15:8: warning: left shift count is negative [-Wshift-count-negative] > j = 1 << -2048; > ^ > [root@localhost zhongjiang]# ./zj > j = 0 Which is not a surprise because the compiler can detect it as the shift is a constant. oparg is not so constant ... Thanks, tglx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
