The following fixes an oversight when computing alignment in the
vectorizer.
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2016-11-07 Richard Biener <rguent...@suse.de>
PR tree-optimization/78189
* tree-vect-data-refs.c (vect_compute_data_ref_alignment): Fix
alignment computation.
* g++.dg/torture/pr78189.C: New testcase.
Index: gcc/testsuite/g++.dg/torture/pr78189.C
===================================================================
--- gcc/testsuite/g++.dg/torture/pr78189.C (revision 0)
+++ gcc/testsuite/g++.dg/torture/pr78189.C (working copy)
@@ -0,0 +1,41 @@
+/* { dg-do run } */
+/* { dg-additional-options "-ftree-slp-vectorize -fno-vect-cost-model" } */
+
+#include <cstddef>
+
+struct A
+{
+ void * a;
+ void * b;
+};
+
+struct alignas(16) B
+{
+ void * pad;
+ void * misaligned;
+ void * pad2;
+
+ A a;
+
+ void Null();
+};
+
+void B::Null()
+{
+ a.a = nullptr;
+ a.b = nullptr;
+}
+
+void __attribute__((noinline,noclone))
+NullB(void * misalignedPtr)
+{
+ B* b = reinterpret_cast<B*>(reinterpret_cast<char *>(misalignedPtr) -
offsetof(B, misaligned));
+ b->Null();
+}
+
+int main()
+{
+ B b;
+ NullB(&b.misaligned);
+ return 0;
+}
diff --git gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index 9346cfe..b03cb1e 100644
--- gcc/tree-vect-data-refs.c
+++ gcc/tree-vect-data-refs.c
@@ -773,10 +773,25 @@ vect_compute_data_ref_alignment (struct data_reference
*dr)
base = ref;
while (handled_component_p (base))
base = TREE_OPERAND (base, 0);
+ unsigned int base_alignment;
+ unsigned HOST_WIDE_INT base_bitpos;
+ get_object_alignment_1 (base, &base_alignment, &base_bitpos);
+ /* As data-ref analysis strips the MEM_REF down to its base operand
+ to form DR_BASE_ADDRESS and adds the offset to DR_INIT we have to
+ adjust things to make base_alignment valid as the alignment of
+ DR_BASE_ADDRESS. */
if (TREE_CODE (base) == MEM_REF)
- base = build2 (MEM_REF, TREE_TYPE (base), base_addr,
- build_int_cst (TREE_TYPE (TREE_OPERAND (base, 1)), 0));
- unsigned int base_alignment = get_object_alignment (base);
+ {
+ base_bitpos -= mem_ref_offset (base).to_short_addr () * BITS_PER_UNIT;
+ base_bitpos &= (base_alignment - 1);
+ }
+ if (base_bitpos != 0)
+ base_alignment = base_bitpos & -base_bitpos;
+ /* Also look at the alignment of the base address DR analysis
+ computed. */
+ unsigned int base_addr_alignment = get_pointer_alignment (base_addr);
+ if (base_addr_alignment > base_alignment)
+ base_alignment = base_addr_alignment;
if (base_alignment >= TYPE_ALIGN (TREE_TYPE (vectype)))
DR_VECT_AUX (dr)->base_element_aligned = true;
