Does a compiler use all x86 instructions? (2010)

Re:Does a compiler use all x86 instructions? (2010) by rdtsc on Wednesday August 24, 2016 @06:23PM (#12355711)

Right, that's what I mean by pointer arithmetic -- specialized instruction for calculating memory addresses. It seems it can be co-opted to do math and other calculations as well. But at least that was its intended use?

Also Zen of Assembly mentions that LEA can store its result in any register and doesn't alter flags.

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Re:Does a compiler use all x86 instructions? (2010) by efaref on Thursday August 25, 2016 @08:26AM (#12358456)

Yes, I think it was designed in particular for determining addresses of fields within structures and variables on the stack, for example if you had:

    struct foo
    {
       int field1;
       int field2[10];
    }

Then an access like:

    fooptr->field2[index]

Would compile to:

    fooptr + sizeof(int) * index + offsetof(struct foo, field2)

Which is:

    lea $4(fooptr,index,4)

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