just made CXXRTL 20% faster overall (2× faster commits) on clang-11 by replacing a bunch of `flag |= x.commit()` with `if (x.commit()) flag = true;` (gcc-10 is unaffected)
compilers🤦♀️
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what is particularly funny is that clang without the fix is slower than gcc, but clang with the fix is actually 10% faster than gcc
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There are missed optimizations from Clang implementing bool as i8 instead of i1. Range metadata (llvm.org/docs/LangRef.h) is supposed to help with this but doesn't work very well and gets stripped out by transformations. LLVM itself is better at this. Not sure why Clang uses i8.
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Clang similarly doesn't make much use of LLVM aggregates. In general, this is a sign that there's something wrong with the LLVM feature and it isn't a good idea to use it elsewhere if you expect correct and efficient code generation. C ABI support in LLVM is a total hack too.
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Clang manually deals with implementing the C calling convention for structs instead of LLVM's C calling convention implementing it for aggregates. These workarounds in Clang cause many missed optimizations in LLVM, and LLVM also isn't optimized to deal well with first-class code.
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yeah, I've hit that particular issue pretty badly on my projects (then again, who doesn't?)
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I was looking into making i1 work better at one point and had a dozen tiny fixes like lists.llvm.org/pipermail/llvm. I ended up running into some problems that were too hard me to to solve on my own and gave up on the whole project. I never ended up submitting the other fixes I made.
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