80 lines
2.4 KiB
Text
80 lines
2.4 KiB
Text
.NH 2
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External representation of the intermediate code
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.PP
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The syntax of the intermediate code was given
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in the previous section.
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In this section we will make some remarks about
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the representation of the code in sequential files.
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.sp
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We use sequential files in order to avoid
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the bookkeeping of complex file indices.
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As a consequence of this decision
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we can't store all components
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of the intermediate code
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in one file.
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If a phase wishes to change some attribute
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of a procedure,
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or wants to add or delete entire procedures
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(inline substitution may do the latter),
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the procedure table will only be fully updated
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after the entire EM text has been scanned.
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Yet, the next phase undoubtedly wants
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to read the procedure table before it
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starts working on the EM text.
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Hence there is an ordering problem, which
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can be solved easily by putting the
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procedure table in a separate file.
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Similarly, the data block table is kept
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in a file of its own.
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.PP
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The control flow graphs (CFGs) could be mixed
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with the EM text.
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Rather, we have chosen to put them
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in a separate file too.
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The control flow graph file should be regarded as a
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file that imposes some structure on the EM-text file,
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just as an overhead sheet containing a picture
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of a Flow Chart may be put on an overhead sheet
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containing statements.
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The loop tables are also put in the CFG file.
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A loop imposes an extra structure on the
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CFGs and hence on the EM text.
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So there are four files:
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.IP -
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the EM-text file
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.IP -
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the procedure table file
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.IP -
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the object table file
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.IP -
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the CFG and loop tables file
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.LP
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Every table is preceded by its length, in order to
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tell where it ends.
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The CFG file also contains the number of instructions of
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every basic block,
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indicating which part of the EM text belongs
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to that block.
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.DS
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.UL syntax
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intermediate_code:
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object_table_file
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proctable_file
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em_text_file
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cfg_file ;
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object_table_file:
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LENGTH -- number of objects
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object_table ;
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proctable_file:
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LENGTH -- number of procedures
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procedure_table ;
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em_text_file:
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em_text ;
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cfg_file:
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{per_proc} ; -- one for every procedure
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per_proc:
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BLENGTH -- number of basic blocks
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LLENGTH -- number of loops
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control_flow_graph
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looptable ;
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.DE
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