April 3 Lecture Outline Notes


I. Tasks of compilation

- Convert high-level language to machine code
    Obey semantics of source language
    Make efficent use of target machine resources
    Compiler must be adequately efficient too

- Main tasks
    Data placement
    Instruction selection
    Fixed resource allocation (e.g., registers)
    Runtime system design and implementation
  
- Historically, high-level language design has been heavily influenced
  by what people think compiler can do well.

II. Charcteristics of Modern Target Architectures

- (nearly) universal characteristics of machines
    Stored program model (program is just another kind of data)
    Addressable memory 
    Indexed set of registers
    Core of arithmetic/logical operations on integers, usually also FP
    Conditional branches for control flow

- IA32 (X86, Pentium)
    Small number of registers (effectively 6, with some special restrictions)
    Complex instruction set (many addressing modes)
    Lots of optimization (e.g., superscalar issue, out-of-order issue, register shadowing) done in hardware
    
- SPARC (32 or 64 bit versions)
    Larger number of registers (about 30)
    Simple instruction set
    Instruction latencies exposed, so scheduling can make a difference
    
- Key fact of life (this decade): main memory is slow!
    Caches absolutely essential
    Keeping miss rates low is essential
    Processors are pipelined => branches are bad, and unknown branches are very bad
    Data layout can have big impact on miss rates

- standard Operating System assumptions
    Virtual memory (except in embedded systems)
    Separation of static data, growable heap, stack.
    System calls for I/O, etc.
    Multiprocessing with separate address spaces (using hardware support)

- other models to remember: embedded processors, IA64, parallel processors