On Mon, Mar 21, 2016 at 4:22 PM, Bin Cheng <bin.ch...@arm.com> wrote: > Hi, > The second issue revealed by PR69489 is tree ifcvt could not convert PHI > nodes with more than 2 arguments. Among these nodes, there is a special kind > of PHI which can be handled. Precisely, if the PHI node satisfies below two > conditions: > 1) Number of PHI arguments with different values equals to 2 and one > argument has the only occurrence. > 2) The edge corresponding to the unique argument isn't critical edge. > > Such PHI can be degenerated and handled just like PHI node with only two > arguments. For example: > res = PHI <A_1(e1), A_1(e2), A_2(e3), A_1(e4)>; > can be transformed into: > res = (predicate of e3) ? A_2 : A_1; > > This patch fixes the issue. I know we may be able to further relax the check > and allow handling of general multiple args PHI node, this can be a starter > since the change is kind of trivial. > Bootstrap & test on x86_64 & AArch64. Though the first part patch at > https://gcc.gnu.org/ml/gcc-patches/2016-03/msg00888.html needs to be revised, > this one is quite independent apart from the test case itself. So any > opinions?
Looks good to me. Btw, see also PR56541 where jump threading can introduce the case but with more than two distinct PHI args. IMHO we "simply" want to force *amy_mask_load_store to true if if_convertible_phi_p runs into this case (so we perform versioning to only expose the if-converted code to the vectorizer which has a cost model to tell whether the result is profitable). There is still the critical edge splitting only performed for aggressive-if-conv but I think that's easily sth we can do for all loop bodies. Richard. > Thanks, > bin > > 2016-03-21 Bin Cheng <bin.ch...@arm.com> > > PR tree-optimization/69489 > * tree-if-conv.c (phi_convertible_by_degenerating_args): New. > (if_convertible_phi_p): Call phi_convertible_by_degenerating_args. > Revise dump message. > (if_convertible_bb_p): Remove check on edge count of basic block's > predecessors. > > gcc/testsuite/ChangeLog > 2016-03-21 Bin Cheng <bin.ch...@arm.com> > > PR tree-optimization/69489 > * gcc.dg/tree-ssa/ifc-pr69489-2.c: New test.
