[PATCH] tree-optimization/125668 - missed alignment updating from forwprop

[Richard Biener]

With the PR125296 fix I forgot to handle the LHS propagation case.

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

        PR tree-optimization/125668
        * tree-ssa-forwprop.cc (forward_propagate_addr_expr_1):
        Preserve alignment of the original access also for propagating
        into the LHS.

        * gcc.dg/pr125668.c: New testcase.
---
 gcc/testsuite/gcc.dg/pr125668.c | 20 ++++++++++++++++++++
 gcc/tree-ssa-forwprop.cc        |  6 ++++--
 2 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr125668.c

diff --git a/gcc/testsuite/gcc.dg/pr125668.c b/gcc/testsuite/gcc.dg/pr125668.c
new file mode 100644
index 00000000000..4cacc4bd235
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr125668.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-strict-aliasing -fdump-tree-forwprop1-gimple" } */
+
+struct S {
+  long x;
+  int y;
+};
+
+struct S2 {
+  struct S bufs[];
+};
+
+void foo(struct S2 *p, int i)
+{
+  struct S *buf = &p->bufs[i];
+  if (*((volatile int *)&buf->y) < 0)
+    *((volatile int *)&buf->y) = 0;
+}
+
+/* { dg-final { scan-tree-dump-times ", 32>" 2 "forwprop1" { target lp64 } } } 
*/
diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 922e36590fd..9bb001d2f63 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -760,8 +760,10 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs,
              new_base = build_fold_addr_expr (*def_rhs_basep);
              new_offset = TREE_OPERAND (lhs, 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 (lhs)) < TYPE_ALIGN (atype))
+           atype = build_aligned_type (atype, TYPE_ALIGN (TREE_TYPE (lhs)));
+         *def_rhs_basep = build2 (MEM_REF, atype, new_base, new_offset);
          TREE_THIS_VOLATILE (*def_rhs_basep) = TREE_THIS_VOLATILE (lhs);
          TREE_SIDE_EFFECTS (*def_rhs_basep) = TREE_SIDE_EFFECTS (lhs);
          TREE_THIS_NOTRAP (*def_rhs_basep) = TREE_THIS_NOTRAP (lhs);
-- 
2.51.0