On Tue 12-07-16 03:47:42, Chen Gang wrote: [...] > In our case, the 2 output size are same, but under x86_64, the insns are > different. After uses bool, it uses push/pop instead of branch, for me, > it should be a little better for catching. The code generated for bool version looks much worse. Look at the fast path. Gcc tries to reuse the retq from the fast path in the bool case and so it has to push rbp and rbx on the stack. That being said, gcc doesn't seem to generate a better code for bool so I do not think this is really worth it. > The orig: > > 0000000000001290 <PageMovable>: > 1290: 48 8b 47 08 mov 0x8(%rdi),%rax > 1294: 83 e0 03 and $0x3,%eax > 1297: 48 83 f8 02 cmp $0x2,%rax > 129b: 74 03 je 12a0 <__SetPageMovable+0x12a0> > 129d: 31 c0 xor %eax,%eax > 129f: c3 retq > 12a0: 55 push %rbp > 12a1: 48 89 e5 mov %rsp,%rbp > 12a4: e8 00 00 00 00 callq 12a9 <__SetPageMovable+0x12a9> > 12a9: 48 85 c0 test %rax,%rax > 12ac: 74 17 je 12c5 <__SetPageMovable+0x12c5> > 12ae: 48 8b 50 68 mov 0x68(%rax),%rdx > 12b2: 48 85 d2 test %rdx,%rdx > 12b5: 74 0e je 12c5 <__SetPageMovable+0x12c5> > 12b7: 48 83 7a 68 00 cmpq $0x0,0x68(%rdx) > 12bc: b8 01 00 00 00 mov $0x1,%eax > 12c1: 74 02 je 12c5 <__SetPageMovable+0x12c5> > 12c3: 5d pop %rbp > 12c4: c3 retq > 12c5: 31 c0 xor %eax,%eax > 12c7: 5d pop %rbp > 12c8: c3 retq > 12c9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) > > The new: > > 0000000000001290 <PageMovable>: > 1290: 48 8b 47 08 mov 0x8(%rdi),%rax > 1294: 55 push %rbp > 1295: 48 89 e5 mov %rsp,%rbp > 1298: 53 push %rbx > 1299: 31 db xor %ebx,%ebx > 129b: 83 e0 03 and $0x3,%eax > 129e: 48 83 f8 02 cmp $0x2,%rax > 12a2: 74 05 je 12a9 <__SetPageMovable+0x12a9> > 12a4: 89 d8 mov %ebx,%eax > 12a6: 5b pop %rbx > 12a7: 5d pop %rbp > 12a8: c3 retq > 12a9: e8 00 00 00 00 callq 12ae <__SetPageMovable+0x12ae> > 12ae: 48 85 c0 test %rax,%rax > 12b1: 74 f1 je 12a4 <__SetPageMovable+0x12a4> > 12b3: 48 8b 40 68 mov 0x68(%rax),%rax > 12b7: 48 85 c0 test %rax,%rax > 12ba: 74 e8 je 12a4 <__SetPageMovable+0x12a4> > 12bc: 48 83 78 68 00 cmpq $0x0,0x68(%rax) > 12c1: 0f 95 c3 setne %bl > 12c4: 89 d8 mov %ebx,%eax > 12c6: 5b pop %rbx > 12c7: 5d pop %rbp > 12c8: c3 retq > 12c9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) > > Thanks. > -- > Chen Gang (陈刚) > > Managing Natural Environments is the Duty of Human Beings. -- Michal Hocko SUSE Labs -- 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>