The earlier transformations are actually more impressive. Constant folding is almost always has a good RoI, so lots of compilers do it, and it's simple because,

The earlier transformations are actually more impressive. Constant folding is almost always has a good RoI, so lots of compilers do it, and it's simple because, well, it's a constant there is no variables or partial eval needed. The others require lots of inlining before the final rule fires, and so are more ambitious. Seeing what pub fn sum3(n: i32) -> i32 { (1..n).sum() + (1..2*n).sum() + (1..(n + 2)).sum() } does would be more interesting to me. Also, while all the inline is rustc, I assume the "triangle number trick" is LLVM.