------- Comment #6 from vvv at ru dot ru 2009-04-28 21:18 -------
Let's compile file test.c
//#file test.c
extern int F(int m);
void func(int x)
{
int u = F(x);
while (u)
u = F(u)*3+1;
}
# gcc -o t.out test.c -c -O2
# objdump -d t.out
t.out: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <func>:
0: 48 83 ec 08 sub $0x8,%rsp
4: e8 00 00 00 00 callq 9 <func+0x9>
9: 85 c0 test %eax,%eax
b: 89 c7 mov %eax,%edi
d: 74 0e je 1d <func+0x1d>
f: 90 nop
10: e8 00 00 00 00 callq 15 <func+0x15>
15: 8d 7c 40 01 lea 0x1(%rax,%rax,2),%edi
19: 85 ff test %edi,%edi
1b: 75 f3 jne 10 <func+0x10>
1d: 48 83 c4 08 add $0x8,%rsp
21: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) <---- nonoptimal
28: c3 retq
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39942
