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

[Richard Biener]

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

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed to trunk.

        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.
---
 gcc/testsuite/gcc.dg/pr125206.c | 22 ++++++++++++++++++++++
 gcc/tree-ssa-forwprop.cc        |  6 ++++--
 2 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr125206.c

diff --git a/gcc/testsuite/gcc.dg/pr125206.c b/gcc/testsuite/gcc.dg/pr125206.c
new file mode 100644
index 00000000000..81db1f6d45d
--- /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 0d76f85e2ac..1587fa7bd14 100644
--- 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);
-- 
2.51.0