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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20100506/af11583b/attachment.html>
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 On May 6, 2010, at 2:50 AM, ether zhhb wrote:> 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 > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
hi Dan, On Fri, May 7, 2010 at 12:23 AM, Dan Gohman <gohman at apple.com> wrote:> I recently added support for <= loops on trunk.thanks very much, that will help us a lot :)> ScalarEvolution now > uses the nsw flag to prove that it doesn't need to consider the > infinite-loop case. > > Dan > > best regards--ether -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20100507/f20a1c0d/attachment.html>