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A comment on Ask HN: What are some good resources to learn safety-critical C/C++ coding from?. Parent comment

Re:Ask HN: What are some good resources to learn safety-crit... by jbms on Friday August 05, 2022 @07:35PM (#32363198)
If the debug code with no optimisations is the one trusted most, that's what ships.

If the optimiser drops off some code as it thinks it has no effect, I'd guess that's possible to spot, and you'd want to know to either fix the code or remove dead code. I've not personally had to inspect compiler output but I do spend a surprising amount of time in linker map files understanding what's going on.

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Re:Ask HN: What are some good resources to learn safety-crit... by wizofaus on Friday August 05, 2022 @10:22PM (#32364217)
Optimising compilers do a lot more than drop code with no effect (and TBH most decent linter tools will pick that up for you anyway), I've seen them generate machine code that bore virtually no relationship to the C source, with loop unrolling, function call inlining, operation interleaving etc. etc. https://cacm.acm.org/magazines/2020/2/242347-optimizations-i... has some interesting examples.
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Re:Ask HN: What are some good resources to learn safety-crit... by flyingfences on Friday August 05, 2022 @11:34PM (#32364575)
Yup, and that's exactly why we turn the optimizations off and keep them off, even for the shipped release.
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Re:Ask HN: What are some good resources to learn safety-crit... by wizofaus on Friday August 05, 2022 @11:37PM (#32364591)
Makes sense if safety is a priority over performance and/or concerns over reverse engineering.
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Re:Ask HN: What are some good resources to learn safety-crit... by jstimpfle on Saturday August 06, 2022 @05:54AM (#32366597)
For the mostly high-level C code that I write, I find that compiler optimisations give typically give speed-ups in the 1.5x - 3x range. A lot of code is bound by external bottlenecks that would completely mask such a speedup anyway.

For really performance-oriented code you probably want to drop to SIMD first, and play with compiler optimisations second.

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