[llvm-dev] _ExtInt, LLVM integers and constant time

Chris Lattner via llvm-dev llvm-dev at lists.llvm.org
Wed Apr 22 09:13:44 PDT 2020

> On Apr 22, 2020, at 12:24 AM, Roman Lebedev via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> On Wed, Apr 22, 2020 at 9:35 AM Adrien Guinet via llvm-dev
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>> Hello everyone,
>> After reading the nice blog post about _ExtInt, I was wondering whether
>> operations on i128/i256 and more generally on integer types in LLVM are
>> guaranteed to be constant time or not.
> I don't believe there's any such guarantee even for normal 8/16/32/64
> -bit integers.

Right. I would expect this to be implementation / target dependent.  The maximum bit width of an integer may also be target specific.  For example, some targets may not provide a 1024 bit integer divide lib call, and may not want to open code it.

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