Comment by lyinsteve

I don’t know much about rust specifically, but the overflow traps happen in debug (i.e. -O0) builds, and are not emitted when optimizations are enabled.

LLVM’s constant folding and canonicalization passes will convert (x * 2) / 2 from

%0 = mul i64 %x, i64 2

%1 = div i64 %0, i64 2

to

%0 = shl i64 %x, i64 1

%1 = shr i64 %0, i64 1

Which constant folding will reduce to just %x.