Re: Optimization techniques and undefined behavior

George Neuner <gneuner2@comcast.net>
Sat, 04 May 2019 17:44:02 -0400

          From comp.compilers

Related articles
[21 earlier articles]
Re: Optimization techniques and undefined behavior martin@gkc.org.uk (Martin Ward) (2019-05-03)
Re: Optimization techniques and undefined behavior anw@cuboid.co.uk (Andy Walker) (2019-05-03)
Re: Optimization techniques and undefined behavior david.brown@hesbynett.no (David Brown) (2019-05-03)
Re: Optimization techniques and undefined behavior bc@freeuk.com (Bart) (2019-05-03)
Re: Optimization techniques and undefined behavior bc@freeuk.com (Bart) (2019-05-03)
Re: Optimization techniques and undefined behavior anw@cuboid.co.uk (Andy Walker) (2019-05-04)
Re: Optimization techniques and undefined behavior gneuner2@comcast.net (George Neuner) (2019-05-04)
Re: Optimization techniques and undefined behavior gneuner2@comcast.net (George Neuner) (2019-05-04)
Re: Bounds checking, Optimization techniques and undefined behavior gneuner2@comcast.net (George Neuner) (2019-05-05)
Re: Optimization techniques and undefined behavior david.brown@hesbynett.no (David Brown) (2019-05-06)
Re: Optimization techniques and undefined behavior martin@gkc.org.uk (Martin Ward) (2019-05-06)
Re: Optimization techniques and undefined behavior robin51@dodo.com.au (Robin Vowels) (2019-05-07)
Re: Optimization techniques and undefined behavior derek@_NOSPAM_knosof.co.uk (Derek M. Jones) (2019-05-06)
[7 later articles]
| List of all articles for this month |

From: George Neuner <gneuner2@comcast.net>
Newsgroups: comp.compilers
Date: Sat, 04 May 2019 17:44:02 -0400
Organization: A noiseless patient Spider
References: 19-04-021 19-04-023 19-04-037 19-04-039 19-04-042 19-04-044 19-04-047 19-05-004 19-05-006 19-05-016 19-05-017
Injection-Info: gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="77178"; mail-complaints-to="abuse@iecc.com"
Keywords: debug, errors, comment
Posted-Date: 04 May 2019 18:32:15 EDT

On Fri, 3 May 2019 10:52:27 +0100, Martin Ward <martin@gkc.org.uk>
wrote:


>On 2019-05-01, David Brown <david.brown@hesbynett.no> wrote:
>> Detecting signed overflow at run-time can be a significant cost.
>
>Firstly: the cost is not as high as the cost of security breaches due
>to buffer overflows.


Exactly. In well written code, often it is possible to amortize
up-front limit tests over a substantial block of code. Similar to
hoisting common subexpressions.




>Secondly: if many popular languages specified
>suitable handling for signed overflow, buffer overruns and so on, then
>CPUs hardware would be developed which makes these tests efficient:
>because compiled code in these popular languages would run faster on
>such CPUs.


Intel and AMD CPUs have bounds check instructions: but they are
cumbersome (similar to using segments), cause exceptions rather than
setting flags, and the instructions are relatively slow because few
compilers ever used them.


George
[Are you referring to the old BOUND instruction or the newer MPX feature. -John]


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