[llvm-dev] [RFC] Coding Standards: "prefer `int` for regular arithmetic, use `unsigned` only for bitmask and when you intend to rely on wrapping behavior."

Quentin Colombet via llvm-dev llvm-dev at lists.llvm.org
Tue Jun 11 14:33:03 PDT 2019

> On Jun 11, 2019, at 12:59 PM, Zachary Turner via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> On Tue, Jun 11, 2019 at 12:24 PM Mehdi AMINI <joker.eph at gmail.com <mailto:joker.eph at gmail.com>> wrote:
> I agree that readability, maintainability, and ability to debug/find issues are key. 
> I haven't found myself in a situation where unsigned was helping my readability: on the opposite actually I am always wondering where is the expecting wrap-around behavior and that is one more thing I have to keep in mind when I read code that manipulate unsigned. So YMMV but using unsigned *increases* my mental load when reading code.
> I'm on the other end.  I'm always reading the code wondering "is this going to warn?"  "Why could a container ever have a negative number of elements?"  "The maximum value representable by the return type (unsigned) is larger than that of the value i'm storing it in (signed), so an overflow could happen even if there were no error.  What then?”


> On Tue, Jun 11, 2019 at 12:26 PM Michael Kruse <llvmdev at meinersbur.de <mailto:llvmdev at meinersbur.de>> wrote:
> Am Di., 11. Juni 2019 um 11:45 Uhr schrieb Zachary Turner via llvm-dev
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>:
> >
> > I'm personally against changing everything to signed integers.  To me, this is an example of making code strictly less readable and more confusing in order to fight deficiencies in the language standard.  I get the problem that it's solving, but I view this as mostly a theoretical problem, whereas being able to read the code and have it make sense is a practical problem that we must face on a daily basis.  If you change everything to signed integers, you may catch a real problem with it a couple of times a year.  And by "real problem" here, I'm talking about a miscompile or an actual bug that surfaces in production somewhere, rather than a "yes, it seems theoretically possible for this to overflow".
> Doesn't it make it already worth it?
> vector.size() returns a size_t, which on 64-bit platforms can represent types values larger than those that can fit into an int64_t.  So to turn your argument around, since it's theoretically possible to have a vector with more items than an int64_t can represent, isn't it already worth it to use size_t, which is an unsigned type?
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