re PR tree-optimization/80170 (SLP vectorization creates aligned access)

2017-03-27  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/80170
	* tree-vect-data-refs.c (vect_compute_data_ref_alignment): Make
	sure DR/SCEV didnt fold in constants we do not see when looking
	at the reference base alignment.

	* gcc.dg/pr80170.c: New testcase.

From-SVN: r246491

gcc/ChangeLog

 2017-03-27  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/80170
+	* tree-vect-data-refs.c (vect_compute_data_ref_alignment): Make
+	sure DR/SCEV didnt fold in constants we do not see when looking
+	at the reference base alignment.
+
+2017-03-27  Richard Biener  <rguenther@suse.de>
+
 	PR middle-end/80171
 	* gimple-fold.c (fold_ctor_reference): Properly guard against
 	NULL return value from canonicalize_constructor_val.

gcc/testsuite/ChangeLog

 2017-03-27  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/80170
+	* gcc.dg/pr80170.c: New testcase.
+
+2017-03-27  Richard Biener  <rguenther@suse.de>
+
 	PR middle-end/80171
 	* g++.dg/torture/pr80171.C: New testcase.
 

gcc/testsuite/gcc.dg/pr80170.c

+/* { dg-do run } */
+/* { dg-options "-fgimple -O2 -ftree-slp-vectorize" } */
+
+struct  A
+{
+  void * a;
+  void * b;
+};
+
+struct __attribute__((aligned(16))) B
+{
+  void * pad;
+  void * misaligned;
+  void * pad2;
+
+  struct A a;
+};
+
+__attribute__((noclone, noinline))
+void __GIMPLE (startwith("slp"))
+NullB (void * misalignedPtr)
+{
+  struct B * b;
+
+  bb_2:
+#if __SIZEOF_LONG__ == 8
+  b_2 = misalignedPtr_1(D) + 18446744073709551608ul;
+#else
+  b_2 = misalignedPtr_1(D) + 4294967292ul;
+#endif
+  __MEM <struct B> (b_2).a.a = _Literal (void *) 0;
+  __MEM <struct B> (b_2).a.b = _Literal (void *) 0;
+  return;
+
+}
+
+int main()
+{
+  struct B b;
+  NullB (&b.misaligned);
+  return 0;
+}

gcc/tree-vect-data-refs.c

@@ -779,7 +779,7 @@ 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 int base_alignment = 0;
   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
@@ -788,8 +788,17 @@ vect_compute_data_ref_alignment (struct data_reference *dr)
      DR_BASE_ADDRESS.  */
   if (TREE_CODE (base) == MEM_REF)
     {
-      base_bitpos -= mem_ref_offset (base).to_short_addr () * BITS_PER_UNIT;
-      base_bitpos &= (base_alignment - 1);
+      /* Note all this only works if DR_BASE_ADDRESS is the same as
+	 MEM_REF operand zero, otherwise DR/SCEV analysis might have factored
+	 in other offsets.  We need to rework DR to compute the alingment
+	 of DR_BASE_ADDRESS as long as all information is still available.  */
+      if (operand_equal_p (TREE_OPERAND (base, 0), base_addr, 0))
+	{
+	  base_bitpos -= mem_ref_offset (base).to_short_addr () * BITS_PER_UNIT;
+	  base_bitpos &= (base_alignment - 1);
+	}
+      else
+	base_bitpos = BITS_PER_UNIT;
     }
   if (base_bitpos != 0)
     base_alignment = base_bitpos & -base_bitpos;