On Apr 7, 2011, at 14:02, Alex Kodat wrote: > > A programmer, on the other hand, even with only a glimmer of knowledge of > what the program is doing can usually guess which if block is most likely to > be executed so optimize the code for that if block, for example by holding > registers and pointers needed for that if block over the whole loop while > requiring saving and reestablishment of context for the unlikely if blocks. > Programmers make decisions like this all the time without giving it much > thought at all, the cumulative effect being that a compiler can huff and puff > all it wants, it's at an unfair disadvantage and doesn't stand a chance. > While some C compilers have a register directive that gives a hint to > the compiler to try to keep a value in a register, this is a pretty blunt > instrument and only buys one so much. > OTOH, I am led to believe that some Java VMs do dynamic recompilation, monitoring the execution profile and adjusting the sequence of instructions executed accordingly. This is real time information scarcely available to the assembler programmer.
-- gil
