new file mode 100644
@@ -0,0 +1,96 @@
+/* { dg-require-effective-target vect_double } */
+
+#include "tree-vect.h"
+
+double x[1024], y[1024];
+
+void __attribute__((noipa)) foo()
+{
+ for (int i = 0; i < 512; ++i)
+ {
+ x[2*i] = y[i];
+ x[2*i+1] = y[i];
+ }
+}
+
+void __attribute__((noipa)) bar()
+{
+ for (int i = 0; i < 512; ++i)
+ {
+ x[2*i] = y[2*i];
+ x[2*i+1] = y[2*i];
+ }
+}
+
+void __attribute__((noipa)) baz()
+{
+ for (int i = 0; i < 512; ++i)
+ {
+ x[2*i] = y[511-i];
+ x[2*i+1] = y[511-i];
+ }
+}
+
+void __attribute__((noipa)) boo()
+{
+ for (int i = 0; i < 512; ++i)
+ {
+ x[2*i] = y[2*(511-i)];
+ x[2*i+1] = y[2*(511-i)];
+ }
+}
+
+int
+main ()
+{
+ check_vect ();
+
+ for (int i = 0; i < 1024; ++i)
+ {
+ x[i] = 0;
+ y[i] = i;
+ __asm__ volatile ("");
+ }
+
+ foo ();
+ for (int i = 0; i < 1024; ++i)
+ if (x[i] != y[i/2])
+ abort ();
+
+ for (int i = 0; i < 1024; ++i)
+ {
+ x[i] = 0;
+ __asm__ volatile ("");
+ }
+
+ bar ();
+ for (int i = 0; i < 1024; ++i)
+ if (x[i] != y[2*(i/2)])
+ abort ();
+
+ for (int i = 0; i < 1024; ++i)
+ {
+ x[i] = 0;
+ __asm__ volatile ("");
+ }
+
+ baz ();
+ for (int i = 0; i < 1024; ++i)
+ if (x[i] != y[511 - i/2])
+ abort ();
+
+ for (int i = 0; i < 1024; ++i)
+ {
+ x[i] = 0;
+ __asm__ volatile ("");
+ }
+
+ boo ();
+ for (int i = 0; i < 1024; ++i)
+ if (x[i] != y[2*(511 - i/2)])
+ abort ();
+
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "vectorizing stmts using SLP" 2 "vect" } } */
@@ -1109,7 +1109,7 @@ vect_compute_data_ref_alignment (vec_info *vinfo, dr_vec_info *dr_info)
if (tree_int_cst_sgn (drb->step) < 0)
/* PLUS because STEP is negative. */
misalignment += ((TYPE_VECTOR_SUBPARTS (vectype) - 1)
- * TREE_INT_CST_LOW (drb->step));
+ * -TREE_INT_CST_LOW (TYPE_SIZE_UNIT (TREE_TYPE (vectype))));
unsigned int const_misalignment;
if (!known_misalignment (misalignment, vect_align_c, &const_misalignment))
This fixes bogus misalignment calculation for negative steps since an assertion a previous comment indicated no longer holds: /* DR_STEP(dr) is the same as -TYPE_SIZE of the scalar type, otherwise we wouldn't be here. */ Thus the following replaces DR_STEP by -TYPE_SIZE. Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk sofar. Richard. 2020-07-06 Richard Biener <rguenther@suse.de> PR tree-optimization/96075 * tree-vect-data-refs.c (vect_compute_data_ref_alignment): Use TYPE_SIZE_UNIT of the vector component type instead of DR_STEP for the misalignment calculation for negative step. * gcc.dg/vect/slp-46.c: New testcase. --- gcc/testsuite/gcc.dg/vect/slp-46.c | 96 ++++++++++++++++++++++++++++++ gcc/tree-vect-data-refs.c | 2 +- 2 files changed, 97 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/gcc.dg/vect/slp-46.c