On Sat, May 30, 2015 at 7:47 AM, Jeff Law <l...@redhat.com> wrote: > On 05/19/2015 10:12 AM, Aditya K wrote: >> >> w.r.t. the PR48052, here is the patch which finds out if scev would wrap >> or not. >> The patch symbolically evaluates if valid_niter>= loop->nb_iterations is >> true. In that case the scev would not wrap (??). >> Currently, we only look for two special 'patterns', which are sufficient >> to analyze the simple test cases. >> >> valid_niter = ~s (= UNIT_MAX - s) >> We have to prove that valid_niter>= loop->nb_iterations >> >> Pattern1 loop->nb_iterations: s>= e ? s - e : 0 >> Pattern2 loop->nb_iterations: (e - s) -1 >> >> In the first case we prove that valid_niter>= loop->nb_iterations in both >> the cases i.e., when s>=e and when not. >> In the second case we prove valid_niter>= loop->nb_iterations, by simple >> analysis that UINT_MAX>= e is true in all cases. >> >> I haven't tested this patch completely. I'm looking for feedback and any >> scope for improvement. >> >> >> hth, >> -Aditya >> >> >> >> Vectorize loops which has typecast. >> >> 2015-05-19 hiraditya <hiradi...@msn.com> >> >> * gcc.dg/vect/pr48052.c: New test. >> >> gcc/ChangeLog: >> >> 2015-05-19 hiraditya <hiradi...@msn.com> >> >> * tree-ssa-loop-niter.c (fold_binary_cond_p): Fold a conditional >> operation when additional constraints are >> available. >> (fold_binary_minus_p): Fold a subtraction operations of the form >> (A - B -1) when additional constraints are >> available. >> (scev_probably_wraps_p): Use the above two functions to find >> whether valid_niter>= loop->nb_iterations. > > Is any of this work still useful if Bin Cheng's work on improving overflow > detection for scev goes forward? I certainly got the impression that Bin's > work would solve 48052 and others.
Bin is probably the one to answer this. His patches are still on my list of patches to review... Richard. > Jeff >
