[PATCH] Fix PR80334

[Richard Biener]

The following patch makes sure to preserve (mis-)alignment of memory
references when IVOPTs generates TARGET_MEM_REFs for them.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

Richard.

2017-04-06  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/80334
        * tree-ssa-loop-ivopts.c (rewrite_use_address): Properly
        preserve alignment of accesses.

        * g++.dg/torture/pr80334.C: New testcase.

Index: gcc/tree-ssa-loop-ivopts.c
===================================================================
--- gcc/tree-ssa-loop-ivopts.c  (revision 246724)
+++ gcc/tree-ssa-loop-ivopts.c  (working copy)
@@ -7396,7 +7396,11 @@ rewrite_use_address (struct ivopts_data
     base_hint = var_at_stmt (data->current_loop, cand, use->stmt);
 
   iv = var_at_stmt (data->current_loop, cand, use->stmt);
-  ref = create_mem_ref (&bsi, TREE_TYPE (*use->op_p), &aff,
+  tree type = TREE_TYPE (*use->op_p);
+  unsigned int align = get_object_alignment (*use->op_p);
+  if (align != TYPE_ALIGN (type))
+    type = build_aligned_type (type, align);
+  ref = create_mem_ref (&bsi, type, &aff,
                        reference_alias_ptr_type (*use->op_p),
                        iv, base_hint, data->speed);
   copy_ref_info (ref, *use->op_p);
Index: gcc/testsuite/g++.dg/torture/pr80334.C
===================================================================
--- gcc/testsuite/g++.dg/torture/pr80334.C      (nonexistent)
+++ gcc/testsuite/g++.dg/torture/pr80334.C      (working copy)
@@ -0,0 +1,18 @@
+// { dg-do run }
+
+struct A { alignas(16) char c; };
+struct B { A unpacked; char d; } __attribute__((packed));
+
+char x;
+
+int
+main()
+{
+  alignas(16) B b[3];
+  for (int i = 0; i < 3; i++) b[i].unpacked.c = 'a' + i;
+  for (int i = 0; i < 3; i++)
+    {
+      auto a = new A(b[i].unpacked);
+      x = a->c;
+    }
+}