Viewing profile — terrymah

Until yesterday I thought I was the only person in the world who thought the designed behavior was undesirable, though

Things are much better in 2024 in MSVC than they were in 2014. The overhead today is mostly the additional metadata associated with tracking the state, and most of the inline compa…

We had a UB version of noexcept for a very, very long time. __declspec(nothrow), the throw() function specifier, etc.

No, calling throw in a noexcept function is a defined behavior (call std::terminate), and that behavior is not a diagnostic I think maybe WG21 was concerned a compiler engineer wou…

Determining if a function throws is a pretty basic bit of information collected in bottom up codegen (or during pre pass of a whole program optimization) and in no sense NP hard. C…

I think WG21 has been violently against adding additional UB to the language, because of some hacker news articles a decade ago about people being alarmed at null pointer checks be…

Everyone keeps scanning over the inlining issues, which I think are much larger “Zero overhead” refers to the actual functions code gen; there are still tables and stuff that have …

Well, yeah, things can be related to many things, but throwing extern "C"s was one of the motivations as I recall for 'r'. r is about a compiler optimization where we elide the run…

Nah that was mostly about extern "C" functions which technically can't throw (so the noexcept runtime stuff would be optimized out) but in practice there is a ton of code marked ex…

Dude I am going to blow your mind

Oh, cool! I googled myself and someone actually archived the slides from the talk I gave. I think it holds up pretty well today https://github.com/TriangleCppDevelopersGroup/TerryM…

No, we compile in bottom up order, starting with leaf functions, and collecting information about functions as we go. So "not throwing" sort of trickles up when possible to a certa…

It absolutely does, and even better, the compiler deduced "this function doesn't throw" doesn't come with the overhead of implementing noexcept proper

You can't just look at the codegen of the function itself, you also have to consider the metadata, and the overhead of processing any metadata Specifically here (as I said in other…

In MSVC we've also pretty heavily optimized the whole function case such that we no longer have a literal try/catch block around it (I think there is a single bit in our per functi…

Oh man, don't get me started. This was a point in a talk I gave years ago called "Please Please Help the Compiler" (what I thought was a clever cut at the conventional wisdom at th…

I, too, came for the procedurally generated Doom levels and left disappointed

From direct effects, maybe. But no one is immune from the second order effects. Once our customers start going out of business because they are directly exposed, they can't buy our…

It was a joint project, with ms eventually pulling out to work on NT

You sort of have to, since everyone else is doing it.

This is both C and C++ - they share a common backend (c2.dll) where this work was done. They have different front ends (c1.dll / c1xx.dll).

Hmph. You forgot the part where Bubba's friends are watching him drink beer and eat Hungry-Mans, and if they want some, they can force Bubba to throw out all his food and pour all …

I've heard that modern Intel processors have 100 < x < 200 physical registers. I'm not sure they actually document the exact number.

It's complicated, but modern processors actually do have many more registers than you can name in the instructions. They use things like "register renaming" to avoid false conflict…