[llvm-dev] SCEV cannot compute the trip count of Simple loop
Sanjoy Das via llvm-dev
llvm-dev at lists.llvm.org
Fri Sep 16 16:05:46 PDT 2016
Kevin Choi wrote:
> @Sanjoy, what's the issue with <nsw>?
I'll write up something in a central location and share it.
> Moreover, why can't SCEV detect
> that x is loop invariant and just take the diff/incr?
Detecting the loop invariance of x is not the problem. SCEV currently
stumbles on proving that "x + 1" and "x + 3" don't overflow.
If "x + 1" and "x + 3" cannot be proven to overflow then the loop no
longer has a constant trip count of "2". For instance if "x" is
INT_MAX-1 then the loop will run 0 times.
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