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(g77-295.info)Overview of Translation Process

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Overview of Translation Process
===============================

   The order of phases translating source code to the form accepted by
the GBE is:

  1. Stripping punched-card sources (`g77stripcard.c')

  2. Lexing (`lex.c')

  3. Stand-alone statement identification (`sta.c')

  4. Parsing (`stb.c' and `expr.c')

  5. Constructing (`stc.c')

  6. Collecting (`std.c')

  7. Expanding (`ste.c')

   To get a rough idea of how a particularly twisted Fortran statement
gets treated by the passes, consider:

           FORMAT(I2 4H)=(J/
          &   I3)

   The job of `lex.c' is to know enough about Fortran syntax rules to
break the statement up into distinct lexemes without requiring any
feedback from subsequent phases:

     `FORMAT'
     `('
     `I24H'
     `)'
     `='
     `('
     `J'
     `/'
     `I3'
     `)'

   The job of `sta.c' is to figure out the kind of statement, or, at
least, statement form, that sequence of lexemes represent.

   The sooner it can do this (in terms of using the smallest number of
lexemes, starting with the first for each statement), the better,
because that leaves diagnostics for problems beyond the recognition of
the statement form to subsequent phases, which can usually better
describe the nature of the problem.

   In this case, the `=' at "level zero" (not nested within parentheses)
tells `sta.c' that this is an *assignment-form*, not `FORMAT',
statement.

   An assignment-form statement might be a statement-function
definition or an executable assignment statement.

   To make that determination, `sta.c' looks at the first two lexemes.

   Since the second lexeme is `(', the first must represent an array
for this to be an assignment statement, else it's a statement function.

   Either way, `sta.c' hands off the statement to `stb.c' (either its
statement-function parser or its assignment-statement parser).

   `stb.c' forms a statement-specific record containing the pertinent
information.  That information includes a source expression and, for an
assignment statement, a destination expression.  Expressions are parsed
by `expr.c'.

   This record is passed to `stc.c', which copes with the implications
of the statement within the context established by previous statements.

   For example, if it's the first statement in the file or after an
`END' statement, `stc.c' recognizes that, first of all, a main program
unit is now being lexed (and tells that to `std.c' before telling it
about the current statement).

   `stc.c' attaches whatever information it can, usually derived from
the context established by the preceding statements, and passes the
information to `std.c'.

   `std.c' saves this information away, since the GBE cannot cope with
information that might be incomplete at this stage.

   For example, `I3' might later be determined to be an argument to an
alternate `ENTRY' point.

   When `std.c' is told about the end of an external (top-level)
program unit, it passes all the information it has saved away on
statements in that program unit to `ste.c'.

   `ste.c' "expands" each statement, in sequence, by constructing the
appropriate GBE information and calling the appropriate GBE routines.

   Details on the transformational phases follow.  Keep in mind that
Fortran numbering is used, so the first character on a line is column 1,
decimal numbering is used, and so on.

g77stripcard

lex.c

sta.c

stb.c

expr.c

stc.c

std.c

ste.c

Gotchas (Transforming)

TBD (Transforming)