58 lines
1.9 KiB
Plaintext
58 lines
1.9 KiB
Plaintext
|
.bp
|
||
|
|
.NH
|
||
|
|
The Intermediate Code and the IC phase
|
||
|
|
.PP
|
||
|
|
In this chapter the intermediate code of the EM global optimizer
|
||
|
|
will be defined.
|
||
|
|
The 'Intermediate Code construction' phase (IC),
|
||
|
|
which builds the initial intermediate code from
|
||
|
|
EM Compact Assembly Language,
|
||
|
|
will be described.
|
||
|
|
.NH 2
|
||
|
|
Introduction
|
||
|
|
.PP
|
||
|
|
The EM global optimizer is a multi pass program,
|
||
|
|
hence there is a need for an intermediate code.
|
||
|
|
Usually, programs in the Amsterdam Compiler Kit use the
|
||
|
|
Compact Assembly Language format
|
||
|
|
.[~[
|
||
|
|
keizer architecture
|
||
|
|
.], section 11.2]
|
||
|
|
for this purpose.
|
||
|
|
Although this code has some convenient features,
|
||
|
|
such as being compact,
|
||
|
|
it is quite unsuitable in our case,
|
||
|
|
because of a number of reasons.
|
||
|
|
At first, the code lacks global information
|
||
|
|
about whole procedures or whole basic blocks.
|
||
|
|
Second, it uses identifiers ('names') to bind
|
||
|
|
defining and applied occurrences of
|
||
|
|
procedures, data labels and instruction labels.
|
||
|
|
Although this is usual in high level programming
|
||
|
|
languages, it is awkward in an intermediate code
|
||
|
|
that must be read many times.
|
||
|
|
Each pass of the optimizer would have
|
||
|
|
to incorporate an identifier look-up mechanism
|
||
|
|
to associate a defining occurrence with each
|
||
|
|
applied occurrence of an identifier.
|
||
|
|
Finally, EM programs are used to declare blocks of bytes,
|
||
|
|
rather than variables. A 'hol 6' instruction may be used to
|
||
|
|
declare three 2-byte variables.
|
||
|
|
Clearly, the optimizer wants to deal with variables, and
|
||
|
|
not with rows of bytes.
|
||
|
|
.PP
|
||
|
|
To overcome these problems, we have developed a new
|
||
|
|
intermediate code.
|
||
|
|
This code does not merely consist of the EM instructions,
|
||
|
|
but also contains global information in the
|
||
|
|
form of tables and graphs.
|
||
|
|
Before describing the intermediate code we will
|
||
|
|
first leap aside to outline
|
||
|
|
the problems one generally encounters
|
||
|
|
when trying to store complex data structures such as
|
||
|
|
graphs outside the program, i.e. in a file.
|
||
|
|
We trust this will enhance the
|
||
|
|
comprehensibility of the
|
||
|
|
intermediate code definition and the design and implementation
|
||
|
|
of the IC phase.
|