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From: LINNDR%VUENGVAX.BITNET@wiscvm.wisc.EDU
Newsgroups: comp.lang.c
Subject: Use of #pragma
Message-ID: <6966@brl-adm.ARPA>
Date: Fri, 17-Apr-87 17:51:27 EST
Article-I.D.: brl-adm.6966
Posted: Fri Apr 17 17:51:27 1987
Date-Received: Sun, 19-Apr-87 12:59:07 EST
Sender: news@brl-adm.ARPA
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In article <386@sdd.uucp> Daniel Corbett (dc@sdd.uucp) writes:

>    Why not utilize a #pragma NO_OPTIMIZE & a counter pragma #pragma OPTIMIZE
>around code that is to executed as is  Perhaps we can even create various
>classes of pragmas for different optimizations:  #pragma NO_OPTIMIZE LOOPS,
>#pragma NO_OPTIMIZE_STRENGTH, etc.

Since I don't have the dpANS nor the ready cash to get one, I may
be asking a question already answered there.

Is there a mechanism for allowing the temporary change of compilation
state (presumably with #pragma)? In the context of the statements quoted
above, could I turn optimization off around a particular set of statements
and then return to the optimization state previously in effect? This is
somewhat analogous to lambda-binding in LISP. If my question is unclear,
maybe the following example will clarify.

Suppose I have a file containing some expressions that should not EVER be
optimized in the midst of expressions that might of might not be optimized
depending on the command line arguments.

I could have
!       <stuff 1>
!       #pragma NO_OPTIMIZE
!       <stuff that should not be optimized>
!       #pragma OPTIMIZE
!       <stuff 2)

If my compiler has a -Ox switch to govern the level of optimization,
where x is in the set {1,2,3}, and I say

% cc -O2 example.c

Is <stuff 2> optimized at the same level (2) as <stuff 1>?

I realize the OPTIMIZE may not even be a pragma in a given compiler, but
hopefully the more general question can be understood from this example.

David Linn
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