tree-optimization/125296 - preserve alignment of access with address forwarding

The following makes sure to preserve the alignment of the access
and not pick up that of parts of the address we forward.

	PR tree-optimization/125296
	* tree-ssa-forwprop.cc (forward_propagate_addr_expr_1):
	Preserve alignment of the original access.

	* gcc.dg/pr125206.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/pr125206.c b/gcc/testsuite/gcc.dg/pr125206.c
new file mode 100644 (file)
index 0000000..81db1f6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr125206.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fgimple -fdump-tree-forwprop1-gimple" } */
+
+struct S {
+  struct S *next;
+  int vals[5];
+};
+
+int __GIMPLE foo (struct S * s, int idx)
+{
+  int D_2968;
+  int *_1;
+
+  /* In GIMPLE '*s' does not have to be aligned according to its type
+     so we have to preserve the alignment of the access when forwarding
+     the address.  */
+  _1 = &s->vals[idx];
+  D_2968 = __MEM <volatile int> ((volatile int *)_1);
+  return D_2968;
+}
+
+/* { dg-final { scan-tree-dump "__MEM <struct S, 32>" "forwprop1" { target lp64 } } } */

diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 0d76f85e2acff61ab9c6d427898b8525d38e191e..1587fa7bd14285686d4dba93d95e51a84fa7ee19 100644 (file)
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -856,8 +856,10 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
              new_base = build_fold_addr_expr (*def_rhs_basep);
              new_offset = TREE_OPERAND (rhs, 1);
            }
-         *def_rhs_basep = build2 (MEM_REF, TREE_TYPE (*def_rhs_basep),
-                                  new_base, new_offset);
+         tree atype = TREE_TYPE (*def_rhs_basep);
+         if (TYPE_ALIGN (TREE_TYPE (rhs)) < TYPE_ALIGN (atype))
+           atype = build_aligned_type (atype, TYPE_ALIGN (TREE_TYPE (rhs)));
+         *def_rhs_basep = build2 (MEM_REF, atype, new_base, new_offset);
          TREE_THIS_VOLATILE (*def_rhs_basep) = TREE_THIS_VOLATILE (rhs);
          TREE_SIDE_EFFECTS (*def_rhs_basep) = TREE_SIDE_EFFECTS (rhs);
          TREE_THIS_NOTRAP (*def_rhs_basep) = TREE_THIS_NOTRAP (rhs);