dotnet/runtime
CSE seems to fail when writing `x / cns` and `x % cns` for unsigned integers
Aberta
#119.131 aberto em 27 de ago. de 2025
area-CodeGen-coreclrhelp wantedtenet-performance
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Description
Description
CSE seems to fail if I write something like:
uint Natural(uint index)
{
uint arrIndex = index / 3;
uint bitIndex = index % 3;
return arrIndex + bitIndex;
}
(it does the division twice).
This seems to only be an issue for unsigned integers not using DivRem.
Configuration
Seems to reproduce on any .NET version on godbolt - I've only checked the issue on x64.
Regression?
Probably not.
Analysis
@tannergooding was saying it seems that UMOD might be missing early expansion altogether & it's getting carried down to rationalisation.