optimization/code quality

modrall@world.std.com (Mark W Modrall)
Wed, 3 Feb 1993 14:53:21 GMT

          From comp.compilers

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Newsgroups: comp.compilers
From: modrall@world.std.com (Mark W Modrall)
Keywords: architecture, optimize
Organization: Compilers Central
References: 93-01-180 93-02-021
Date: Wed, 3 Feb 1993 14:53:21 GMT

>There's a rather large switch inside, and the compiler manages to mess up
>its table, and generate eronous code, or backend failures. Which get fixed
>once in a while by using level 3 optimisation. (Hence I knew the time.)
>Supposedly GCC has some of the same features, most compilers are not very
>often exersized at the nopt. level and have relatively more bugs in that

One of my favorite compiler experiences was with the compiler on a
Concurrent system... when you turned on level 3 optimization, you would
occasionally see a diagnostic message pop up during compilation "I-Overuse
of registers, see manual for more information"

Well, none of the resultant code worked... i saw that message, and said
"it's informational, that can't be it." finally, at the end of my rope, I
looked at the manual for more information, and the note said, basically,
"We didn't get this level of optimization right. It generates bad code."

I called up Concurrent and filed a bug report that read "User is appalled
by the classification of this error message."


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