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It feels like a better fi= x than >> >> stubbing things out. >> >>=20 >> >> Best, >> >> Gary >> >> =20 >> > The issue is not coming from libcore itself. It's the driver that's >> > causing this. =20 >>=20 >> Sorry. I quoted the wrong part. I was asking if compiling libcore with O= 2 gets >> rid of its use of the builtins, as that's what the change this commit is= for. >>=20 >> Formatting of u64 will be needed, so we should make sure that these work= s as >> intended. > > This code (from nolibc) will convert u64 to ascii in any base: > > [snip] > > Not hard to do without any divides at all. I mean, the exact same logic is when LLVM lowers code where divisor is cons= tant. It just that it decides that the multiply-by-inverse lowering shouldn't be = done with `Os`. In this case libcore is provided by Rust (think it as freestanding headers)= , that code is not part of kernel. And currently they just use constant-divis= or divide and have this task performed by LLVM. We could ask Rust to explicitl= y use multiply-by-inverse to avoid generating __udivdi3 in the future, but even i= f we do that it won't be available to already-released Rust compilers.=20 In the mean time we need to workaround this. Best, Gary