https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86725
--- Comment #2 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> --- Author: rsandifo Date: Wed Aug 22 13:02:39 2018 New Revision: 263773 URL: https://gcc.gnu.org/viewcvs?rev=263773&root=gcc&view=rev Log: [1/2] Fix bogus double reduction (PR 86725) This patch is the first part of the fix for PR 86725. We would treat x_1 in: outer1: x_1 = PHI <x_4(outer2), ...>; ... inner: x_2 = ...x_1...; ... x_3 = ...; ... outer2: x_4 = PHI <x_3(inner)>; ... as a double reduction without checking what kind of statement x_2 is. In practice it has to be a phi, since for other x_2, x_1 would simply be a loop invariant that gets used for every inner loop iteration. The idea with doing this patch first is that, by checking x_2 really is a phi, we can hand off the validation of the rest of the reduction to the phi analysis in the inner loop. The test case is a variant of the one in the PR. 2018-08-22 Richard Sandiford <richard.sandif...@arm.com> gcc/ PR tree-optimization/86725 * tree-vect-loop.c (vect_is_simple_reduction): When treating an outer loop phi as a double reduction, make sure that the single user of the phi result is an inner loop phi. gcc/testsuite/ PR tree-optimization/86725 * gcc.dg/vect/no-scevccp-pr86725-1.c: New test. Added: trunk/gcc/testsuite/gcc.dg/vect/no-scevccp-pr86725-1.c Modified: trunk/gcc/ChangeLog trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-vect-loop.c
