Back-edge taken count of loops

hi all,

i am have a project need to compute the back-edge taken count of a loop, and the “getBackedgeTakenCount” function of ScalarEvolution could do this for me.

but later i found that ScalarEvolution could not compute loops with test expression containing a “=”, such as:

void scop_func(long A[], long n) {
long i;

for (i = 1; i<= n; i++)
A[i] = 1;
}

after have a look at the code that computing the back-edge taken count, i found that ScalarEvolution could only compute back-edge taken count if the exit condition is ICMP_NE/ICMP_EQ/ICMP_SLT/ICMP_SGT/ICMP_ULT/ICMP_UGT (ignoring “ComputeBackedgeTakenCountExhaustively”), and the function “SimplifyICmpOperands” will try to convert other conditions to the conditions listed above, by doing something like “i <= n” to “i < n+1”, but it refuse to do that unless it could prove “n + 1” will not cause a overflow.

So, could us just set “n + 1” to the Exact field of BackedgeTakenInfo, and set something like SCEVInfinite to the Max field of BackedgeTakenInfo?

thanks
ether

I recently added support for <= loops on trunk. ScalarEvolution now
uses the nsw flag to prove that it doesn't need to consider the
infinite-loop case.

Dan

hi Dan,

I recently added support for <= loops on trunk.

thanks very much, that will help us a lot :slight_smile:

ScalarEvolution now
uses the nsw flag to prove that it doesn’t need to consider the
infinite-loop case.

Dan

best regards
–ether