middle-end/118684 - wrongly aligned stack local during expansion

The following fixes a not properly aligned stack temporary created
during RTL expansion of a MEM_REF that we handle as a BIT_FIELD_REF
whose base was allocated to a register but which was originally
aligned to allow a larger load not trapping.  While probably UB
in C the vectorizer creates aligned accesses that might overread
a (static) allocation because it is then known not to trap.

	PR middle-end/118684
	* expr.cc (expand_expr_real_1): When expanding a reference
	based on a register and we end up needing a MEM make sure
	that's aligned as the original reference required.

	* gcc.dg/pr118684.c: New testcase.

diff --git a/gcc/expr.cc b/gcc/expr.cc
index a06411e1c27642acc1c5f5b755c9f827c9da9109..95f41f69fcf2e114026e440e6b2beaa33de3008b 100644 (file)
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -12148,7 +12148,11 @@ expand_expr_real_1 (tree exp, rtx target, machine_mode tmode,
           and need be, put it there.  */
        else if (CONSTANT_P (op0) || (!MEM_P (op0) && must_force_mem))
          {
-           memloc = assign_temp (TREE_TYPE (tem), 1, 1);
+           poly_int64 size;
+           if (!poly_int_tree_p (TYPE_SIZE_UNIT (TREE_TYPE (tem)), &size))
+             size = max_int_size_in_bytes (TREE_TYPE (tem));
+           memloc = assign_stack_local (TYPE_MODE (TREE_TYPE (tem)), size,
+                                        get_object_alignment (tem));
            emit_move_insn (memloc, op0);
            op0 = memloc;
            clear_mem_expr = true;

diff --git a/gcc/testsuite/gcc.dg/pr118684.c b/gcc/testsuite/gcc.dg/pr118684.c
new file mode 100644 (file)
index 0000000..08cc24d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr118684.c
@@ -0,0 +1,12 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+typedef int v4si __attribute__((vector_size(16)));
+v4si x;
+int main ()
+{
+  int b __attribute__((aligned(16)));
+  b = 0;
+  x = *(v4si *)&b;
+  return 0;
+}