jose gomez valcarcel <jcgv33@xxxxxxxx> writes: > For curiosity, today i test this code with the intel compiler (12.0.5.220). It generates this code for fn: > > icc -O2 -fomit-frame-pointer -c z.c > > > 0000000000000000 <fn>: > 0:56 push %rsi > 1:e8 00 00 00 00 callq 6 <fn+0x6> > 6:48 03 c2 add %rdx,%rax > 9:59 pop %rcx > a:c3 retq > > Yo can see the code changes the values of registers RSI and RCX with apparently no reason ! (appart of computing correctly the c code of fn). > Also this code uses stack with apparently no reason, or i can not see it. The stack has to be aligned at a 16-byte boundary before the function call. The function call itself pushes 8 bytes onto the stack. So another 8 byte adjustment is required before making another function call. icc is choosing to do that adjustment using push and pop. I don't know why that is preferable to adding and subtracting a constant, but there may well be a reason. Ian
