Hardware Trends

Trends in modern CPU architecture present new demands and opportunities for the compiler writer:

• Larger memories: expansion of code size is not as costly as before; might trade code size for speed.

• The compiler can coexist with the running program, for just-in-time compilation.

• High cost for cache misses: a cache miss can cause the CPU to stall (wait) for many execution cycles. Code may be reordered to avoid cache misses.

• Multiple processors: using the processors effectively (getting a speedup of n from n processors) is a difficult challenge. Strip mining may be used to send parts of loops (and memory) to different processors.

• Superscalar architecture: code may be re-ordered to take advantage of out-of-order and speculative execution.

• As number of transistors on chip increases, things that were software become hardware: math subroutines, message passing, memoization, dynamic optimization.