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Comment by plumefar | Hacker News Reader

In my +- 25 years of experience, I've encountered exactly 1 compiler bug. That cost me a full week of debug. Unfortunately, it happened during my very first year as a developer, and that triggered sub-optimal debugging practices (ie: is that the compiler fault again?)

At the end of the day, you want to optimise for debug time. There's the probability that it's a compiler/developer bug (respectively very low/very high) and the time it takes to rule it out. It's of course best NOT to start by investigating the compiler bug.

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I find several every year. Most people simply don't see compiler bugs because they don't test (and most of the time don't need to) their compilers extensively enough (by testing I mean they must build, run the generated binaries, and compare the output ).

That sounds very weird, unless you are working

1) With with an esoteric environment that has relatively few users.

2) Have specific objectives that require a lot of edge case testing or ridiculously thorough fuzzing of the binary.

3) Go out looking for them by crafting nifty things that aren't much used.

Otherwise it would imply large companies (Google-scale) experience thousands of compiler bugs per year...

> Otherwise it would imply large companies (Google-scale) experience thousands of compiler bugs per year...

This seems likely to be true, from my experience.

Fortunately, most compiler bugs I run into (mostly with gcc and llvm) are not code generation bugs (which can eat months of debugging), but just segfaults / rejecting correct code / other broken stuff.

I also suspect most programmers spend most of their time staying more or less on the “straight and narrow”. There’s lots of obscure features in most languages (especially in old languages like C++) that not many programmers use.

These features are much more likely to have buggy edge cases in the compiler. And only a small select group of programmers will run into those bugs over and over again.

Eg complex template metaprogramming - which had known broken corner cases in all C++ compilers up until a decade or so ago.

If you don't hit compiler bugs, it's mostly because you're not updating your compiler.

Large companies with compiler teams want to use them, so they do update their compiler, so they will find bugs in it.

Btw, what do you think this prints with clang? (Whether the answer is a compiler bug is debatable…)

   printf("%#x\n", 1 << 32);

Assuming int is 32 bits wide, `1 << 32` invokes UB.

Indeed it does.

(Spoiler: it prints uninitialized stack memory. A bit closer to demons flying out your nose than you'd expect!)

Fun. Basically, it decides that (due to UB) it can simply not materialize the argument and carry on.

On Darwin/x86_64, this actually means that it prints out bits from an "uninitialized" register, specifically %rsi in this case, since that's where the second argument should be (even for variadic functions).

Certainly a jarring failure mode! However, if updating your compiler causes you to run into this, you already have a bug in your code (one that clang -- arguably not forcefully enough -- already warns you of).

This is exactly when I find most of my compiler bugs : every time we upgrade.

They most likely do (just look at the gcc bugzilla).

I find them because of a combination of : - a very large codebase - compiling with optimizations (O3) and targeting recent archs - yearly compiler upgrades - an extremely extensive testsuite

I have found all kinds of bugs (frontend, middle, backend) - the codegen ones tend to be very nasty to diagnose.

Yeah I was debugging an issue that was occurring in a Kubernetes environment last night... kept wanting to blame the out of date Istio version. I just could not trust it and that lack of trust stopped me from seeing the whitespace error that was in front of me the whole time...

I think it's really dependent of the domain you are working in. Some stuff is better tested than others. In my 5 years careers I found bugs (found and confirmed by compiler authors) in gfortran, xlf and pgfortran. So yes bugs in compilers are rare but sometimes you just keep running into them.

those are quite niche languages though, most people use compilers which are much more widely used.

Clang support for AVX-512 intrinsics is pretty broken

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