On Tue, Feb 22, 2022 at 1:00 PM William Tambe <tambewilliam@xxxxxxxxx> wrote: > > In this CPU, > > A multi-cycle instruction, once decoded, runs in parallel as other > decoded single/multi-cycle instructions. > > A single/multi-cycle instruction takes two operands, where the first > operand receives the result > of computing both operands. > > An example of multi-cycle instruction is "div". > An example of single-cycle instruction is "add". > > GCC should be able to transform following: > ```` > add %0 %5 > add %1 %6 > div %4 %5 #<-- Multi-cycle instruction. > add %4 %7 #<-- Next instruction that depends on its result. > add %3 %7 > add %2 %7 > ``` > To: > ``` > div %4 %5 #<-- Multi-cycle instruction. > add %0 %5 > add %1 %6 > add %3 %7 > add %2 %7 > add %4 %7 #<-- Next instruction that depends on its result. > ``` > Without above transformation, `add %4 %7` would cause the cpu to wait > on `div %4 %5` when it could have executed instructions that do not > depend on the result of "div". How to implement above transformation such that GCC moves instructions between a multi-cycle instruction and the next instruction that depends on its result ?
