Created
May 11, 2012 18:28
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C addition disassembly
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int i = 1; | |
i += ++i + ++i; | |
.. disassembly of above (compiled with gcc 4.2 with no optimizations): | |
>> x = 1 | |
0000000100000f14 movl $0x00000001,0xf8(%rbp) | |
>> ++x | |
0000000100000f1b movl 0xf8(%rbp),%eax | |
0000000100000f1e addl $0x01,%eax | |
0000000100000f21 movl %eax,0xf8(%rbp) | |
>> ++x | |
0000000100000f24 movl 0xf8(%rbp),%eax | |
0000000100000f27 addl $0x01,%eax | |
0000000100000f2a movl %eax,0xf8(%rbp) | |
>> now adds the value of the newly incremented x (now 3) to itself twice | |
0000000100000f2d movl 0xf8(%rbp),%eax | |
0000000100000f30 movl 0xf8(%rbp),%ecx | |
0000000100000f33 addl %ecx,%eax | |
0000000100000f35 movl 0xf8(%rbp),%ecx | |
0000000100000f38 addl %ecx,%eax | |
>> puts 9 back into x | |
0000000100000f3a movl %eax,0xf8(%rbp) | |
.. | |
WITH optimizations at -O4, it just turns into 9 right away ;-) |
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