NodeBuilder Errors Guide 5-33
NCC# Description
247 Statement deleted by optimizer [NCC#247]
The Neuron C compiler's optimizer deletes statements for a variety of
reasons. For example, the statement may represent unnecessary
work, the statement may represent dead (i.e. unreachable) code, or
the optimizer has combined the statement with another statement.
This informatory message is issued for two reasons. First, to let the
programmer know why a breakpoint cannot be set on what looks like
an acceptable statement. Second, to point out code that may never
be executed due to erroneous program logic. Consider the following
examples:
<statements>
goto LABEL;
<statements> //deleted by optimizer
LABEL:
<statements>
Since the goto statement causes a branch around code such that it
can never be executed, the compiler issues a "Statement deleted"
message for each statement. The last example demonstrates an
error in program logic discovered by the compiler. The next example
demonstrates unnecessary statements deleted by the optimizer:
int i;
switch (i) {
case 0:
<statements>
break;
case 1:
<statements>
break;
case 2:
<statements>
break; // deleted by optimizer
}
In the above example, the last break statement in the switch
statement is unnecessary, since execution flow is the same with or
without the break statement. (However, it is recommended that the
statement be coded as shown anyway, because doing so will make
future maintenance of the code easier and less error-prone. It is good
programming practice.)
The optimizer recognizes that any branch is unnecessary and
eliminates the unnecessary branch instruction. The informatory
message is produced to explain why a breakpoint cannot be set at
what appears to be a valid statement. No breakpoint can be set,
since no code actually exists for this statement. Note that
informatory messages are not produced by the compiler unless they
are enabled by the #pragma fyi_on directive.
