Re: Undefined Behavior Optimizations in C

Martin Ward <martin@gkc.org.uk>
Mon, 23 Jan 2023 17:12:14 +0000

          From comp.compilers
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Re: Undefined Behavior Optimizations in C gah4@u.washington.edu (gah4) (2023-01-20)
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Re: Undefined Behavior Optimizations in C martin@gkc.org.uk (Martin Ward) (2023-01-23)
Re: Undefined Behavior Optimizations in C gah4@u.washington.edu (gah4) (2023-01-23)
Re: Undefined Behavior Optimizations in C dave_thompson_2@comcast.net (2023-01-28)
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From: Martin Ward <martin@gkc.org.uk>
Newsgroups: comp.compilers
Date: Mon, 23 Jan 2023 17:12:14 +0000
Organization: Compilers Central
References: 23-01-027 <sympa.1673343321.1624.383@lists.iecc.com> 23-01-031 23-01-041 23-01-062
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Keywords: C, optimize
Posted-Date: 23 Jan 2023 13:27:46 EST

On 18/01/2023 13:14, Spiros Bousbouras wrote:


There's no assumption that UB (undefined behaviour) will not happen, both
possibilities are accounted for.




The "assumption that UB will not happen" is shorthand for the idea
that any optimisation is valid if the optimised code is a refinement
of the unoptimised code for all initial states such that UB does not
occur. Equivalently, a proposed optimiation is valid if we represent
UB as "abort" (a statement which can be refined to anything) and the
optimised code is a refinement of the unoptimised code for all initial
states.


--
                        Martin


Dr Martin Ward | Email: martin@gkc.org.uk | http://www.gkc.org.uk
G.K.Chesterton site: http://www.gkc.org.uk/gkc | Erdos number: 4

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