Inductions are not vectorized as cycle but materialized from SCEV data.
Filling in backedge SLP nodes confuses this process.
Bootstrapped / tested on x86_64-unknown-linux-gnu, pushed.
2020-10-21 Richard Biener <rguent...@suse.de>
PR tree-optimization/97500
* tree-vect-slp.c (vect_analyze_slp_backedges): Do not
fill backedges for inductions.
* gfortran.dg/pr97500.f90: New testcase.
---
gcc/testsuite/gfortran.dg/pr97500.f90 | 35 +++++++++++++++++++++++++++
gcc/tree-vect-slp.c | 6 +++++
2 files changed, 41 insertions(+)
create mode 100644 gcc/testsuite/gfortran.dg/pr97500.f90
diff --git a/gcc/testsuite/gfortran.dg/pr97500.f90
b/gcc/testsuite/gfortran.dg/pr97500.f90
new file mode 100644
index 00000000000..d63b8616ad6
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr97500.f90
@@ -0,0 +1,35 @@
+! { dg-do run }
+! { dg-additional-options "-ftree-vectorize -fno-guess-branch-probability" }
+module testmod
+ implicit none
+
+ contains
+
+ subroutine foo(n)
+ integer, intent(in) :: n
+ real :: r(0:n,-n:n), a(0:n,-n:n), dj
+ integer :: k, j
+
+ ! initialize with some dummy values
+ do j = -n, n
+ a(:, j) = j
+ r(:,j) = j + 1
+ end do
+
+ ! here be dragons
+ do k = 0, n
+ dj = r(k, k - 2) * a(k, k - 2)
+ r(k,k) = a(k, k - 1) * dj
+ enddo
+
+ if (r(0,0) .ne. -2.) STOP 1
+
+ end subroutine
+
+end module
+
+program test
+ use testmod
+ implicit none
+ call foo(5)
+end program
diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index 0c1447e7aa0..e3f94cb8a2d 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -2380,6 +2380,12 @@ vect_analyze_slp_backedges (vec_info *vinfo, slp_tree
node,
if (child)
vect_analyze_slp_backedges (vinfo, child, bst_map, visited);
+ /* Inductions are not vectorized by vectorizing their defining cycle
+ but by materializing the values from SCEV data. */
+ if (STMT_VINFO_DEF_TYPE (SLP_TREE_REPRESENTATIVE (node))
+ == vect_induction_def)
+ return;
+
if (gphi *phi = dyn_cast <gphi *> (SLP_TREE_REPRESENTATIVE (node)->stmt))
for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i)
{
--
2.26.2
