https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69615
--- Comment #3 from Peter Cordes <peter at cordes dot ca> ---
@Richard and Jakub:
That's just addressing the first part of my report, the problem with x <=
(INT_MAX-1), right?
You may have missed the second part of the problem, since I probably buried it
under too much detail with the first:
In the case where the limit is variable, but can easily be proven to itself be
in the range [0 .. INT_MAX-1) or much smaller:
// gcc always fails to optimize this to an unsigned compare, but clang succeeds
void rangecheck_var(int64_t x, int64_t lim2) {
//lim2 >>= 60;
lim2 &= 0xf; // let the compiler figure out the limited range of limit
if (x>=0 && x<lim2) ext();
}
---
I noticed after I submitted the report that I maybe should have tagged it
tree-optimization, thanks for fixing. I don't really know gcc internals; I
just file reports when it makes less than optimal code.
