Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?)

tli@%phakt.usc.edu (Tony Li)
Thu, 7 Jun 90 19:03:15 GMT

          From comp.compilers

Related articles
[3 earlier articles]
Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?) mike@hpfcso.hp.com (1990-06-05)
Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?) pardo@cs.washington.edu (1990-06-05)
Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?) robinson@cs.dal.ca (1990-06-05)
Unsafe Optimizations (WAS: Compiler Design in C How about it?) stewart@sdsu.edu (1990-06-05)
Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?) poser@csli.stanford.edu (1990-06-06)
Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?) larus@primost.cs.wisc.edu (1990-06-07)
Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?) tli@%phakt.usc.edu (1990-06-07)
Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?) moss@cs.umass.edu (1990-06-10)
Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?) cwitty@csli.Stanford.EDU (1990-06-14)
Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?) moss@cs.umass.edu (1990-06-14)
Re: Unsafe Optimizations (WAS: Compiler Design in C How about it?) pardo@june.cs.washington.edu (1990-06-15)
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Newsgroups: comp.compilers
From: tli@%phakt.usc.edu (Tony Li)
References: <1990Jun1.194941.5781@esegue.segue.boston.ma.us> <1990Jun4.212226.18389@esegue.segue.boston.ma.us> <1990Jun7.010349.2097@esegue.segue.boston.ma.us>
Date: Thu, 7 Jun 90 19:03:15 GMT
Organization: University of Southern California, Los Angeles, CA
Keywords: optimize, parallel

In article <1990Jun7.010349.2097@esegue.segue.boston.ma.us> larus@primost.cs.wisc.edu (James Larus) writes:


        Although parallel prefix may produce a different result, which is
        right and which is wrong?


That depends. If the semantics of the language specifies an order of
evaluation, then a "correct" compiler must implement that order of evaluation.




If your optimizer does something different then it is either a) broken, or b)
implementing a different semantics, which is a different language. If you
claim that your compiler correctly implements language X and you choose option
b, then you mislead your customers. You may claim that your compiler
implements extensions to language X, but if you do so, I would expect the
manual to describe the differences clearly. For example, I would expect that
your optimizer switch would tell me in big, blinking red letters that it
introduces nonstandard semantics.


Tony Li - USC Computer Science Department
Internet: tli@usc.edu Uucp: usc!tli
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