27 lines
1 KiB
Plaintext
27 lines
1 KiB
Plaintext
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.NH 2
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Pointers and subroutine calls
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.PP
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The theory outlined above assumes that variables can
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only be changed by a direct assignment.
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This condition does not hold for EM.
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In case of an assignment through a pointer variable,
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it is in general impossible to see which variable is affected
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by the assignment.
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Similar problems occur in the presence of procedure calls.
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Therefore we distinguish two kinds of definitions:
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.IP -
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an \fIexplicit\fR definition is a direct assignment to one
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specific variable
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.IP -
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an \fIimplicit\fR definition is the potential alteration of
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a variable as a result of a procedure call or an indirect assignment.
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.LP
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An indirect assignment causes implicit definitions to
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all variables that may be accessed indirectly, i.e.
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all local variables for which no register message was generated
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and all global variables.
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If a procedure contains an indirect assignment it may change the
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same set of variables, else it may change some global variables directly.
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The KILL, GEN, IN and OUT sets contain explicit as well
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as implicit definitions.
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