[LLVMdev] Back-edge taken count of loops

[ether zhhb]

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
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