[llvm-dev] Unsigned int displaying as negative

Jonas Maebe via llvm-dev llvm-dev at lists.llvm.org
Thu Feb 16 11:35:55 PST 2017

On 16/02/17 20:23, Tim Northover via llvm-dev wrote:
> Saturation is overflow, which means it's not allowed in C for unsigned
> integer types (they have to wrap) and irrelevant for signed (as soon
> as you overflow you're in undefined behaviour territory). LLVM IR
> follows C and doesn't represent saturation -- in particular
> optimization passes before CodeGen will be very happy to change your
> results if you're relying on it, with or without "nsw".

Surely "signed overflow" does not result in undefined behaviour in LLVM 
IR unless nsw is specified? Otherwise, the wording at 
http://llvm.org/docs/LangRef.html should be changed, because right now 
it strongly suggests to me that signed overflow will not cause any 
problems unless nsw is specified.


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