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