Displaying 1 result from an estimated 1 matches for "len_1".
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len1
2017 Dec 21
2
Pass ordering - GVN vs. loop optimizations
...at if a loop index only
appears behind a pointer, LLVM will not be able to optimize out bounds
checks depending on it.
The "canonical" example is this Rust function (or the similar C code):
#![crate_type="rlib"]
pub fn f(length: &usize) -> u64 {
let mut sum = 0;
let len_1 = *length;
let mut i = 0;
while i < len_1 {
let len_2 = *length;
assert!(i < len_2);
i += 1;
}
sum
}
One would expect the assertion (which in a real example is a bounds check)
to be optimized out. However, IndVarSimplify is the optimization that is
supposed to do that, an...