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From: mlight@hp-ptp.HP.COM (Mike Light)
Newsgroups: comp.sys.hp
Subject: Re: C Compiler Optimizer
Message-ID: <1320045@hp-ptp.HP.COM>
Date: 28 Aug 90 17:11:21 GMT
References: <59169@bbn.BBN.COM>
Organization: HP Pacific Technology Park - Sunnyvale, Ca.
Lines: 23

>	We have experienced problems of varying symptoms while using
>the optimizer switch of the HP-UX 7.0 C compiler.  Rather than 
>extensively analyzing these problems we have opted to compile without
>optimizing.  Has anyone else noticed bad behavior with the optimizer?


There is one common symptom, particularly with level 2 optimization:

  The larger the function, the much longer it takes to optimize and the more
swap space you need.  Some of my complex yacc C outputs take up to 40 minutes
each to optimize (even on a 9000/850) and consume about 12 Megabytes of
swap space in the process.  On my 360 the compilation went on and on and on
until in exasperation (after 6 hours) I killed it and used the +O1 switch
which took less than 2 minutes.

  There may be no way to "fix" the optimizer, but rather just choose
the most appropriate optimization for the function.  Lex and yacc outputs
are particularly prone to optimization time warps, and I habitually specify
+O1 for them now.

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 Mike Light  HP Industrial Applications Center - mlight@hpiala9.HP.COM
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