Compiler design is a fascinating topic. I believe it is this together
with operating systems that really got me "hooked" on computers. I
couldn't put down Andrew Tanenbaum's MINIX book, it was simply
fascinating. Of course, at the time I was working on my degree in
mathematics. For some reason or another it never occurred to me to
actually study computer science, I just picked up textbooks and read
them "on the sly".
===
Gregory Woodhouse
[EMAIL PROTECTED]
"Education is a progressive discovery
of our own ignorance."
--Will Durant
On Jul 17, 2005, at 10:00 PM, Gregory Woodhouse wrote:
Compilers don't really generate assembly code (at least not
anymore), but the -S option requests the compiler to produce a file
containing a (PowerPC in this case) assembly language file
representing the machine code that is actually generated.
Typically, compilers will rewrite code considerably for the sake of
efficiency. To understand why, keep in mind that not all operations
take the same amount of time: retrieving a value from a register is
orders of magnitude faster than retrieving the same value from main
memory (because DRAM is slow, and it typically will take about 4
bus cycles, anyway). To get an idea of what kinds of
"modifications" the compiler makes to your code, consider a program
in which you set a variable, e.g. with something like
SET X=1
but you never, ever change the value of X. Then, it would be
extremely wasteful to translate
SET Y=Y+X
by retrieving the value of X and then adding it to (the value of
Y). Typically, operations at the digital logic level will execute
in nanoseconds (or better), but a memory reference might take 10
microseconds (or worse). And that, of course, assumes on board memory.
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