gimple-fold: Fix up __builtin_clear_padding on classes with virtual inheritence ...

For the following testcase, B is 16-byte type, containing 8-byte
virtual pointer and 1-byte A member, and C contains two FIELD_DECLs,
one with B type and size of just 8-byte and then a field with type
A and 1-byte size.
The __builtin_clear_padding code was upset about the B typed FIELD_DECL
containing FIELD_DECLs beyond the field size and triggered
assertion failure.
This patch makes it ignore all FIELD_DECLs that are (fully) beyond the sz
passed from the caller (except for the flexible array member
diagnostics that is kept).

2021-07-27  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/101586
	* gimple-fold.c (clear_padding_type): Ignore FIELD_DECLs with byte
	positions above or equal to sz except for diagnostics of flexible
	array members.

	* g++.dg/torture/builtin-clear-padding-4.C: New test.

diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index a3afe87..b6f6054 100644 (file)
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -4697,6 +4697,8 @@ clear_padding_type (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
                if (fldsz == 0)
                  continue;
                HOST_WIDE_INT pos = int_byte_position (field);
+               if (pos >= sz)
+                 continue;
                HOST_WIDE_INT bpos
                  = tree_to_uhwi (DECL_FIELD_BIT_OFFSET (field));
                bpos %= BITS_PER_UNIT;
@@ -4772,6 +4774,8 @@ clear_padding_type (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
            else
              {
                HOST_WIDE_INT pos = int_byte_position (field);
+               if (pos >= sz)
+                 continue;
                HOST_WIDE_INT fldsz = tree_to_shwi (DECL_SIZE_UNIT (field));
                gcc_assert (pos >= 0 && fldsz >= 0 && pos >= cur_pos);
                clear_padding_add_padding (buf, pos - cur_pos);

diff --git a/gcc/testsuite/g++.dg/torture/builtin-clear-padding-4.C b/gcc/testsuite/g++.dg/torture/builtin-clear-padding-4.C
new file mode 100644 (file)
index 0000000..5936cdf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/builtin-clear-padding-4.C
@@ -0,0 +1,44 @@
+// PR middle-end/101586
+
+struct A { char a; };
+struct B : virtual A {};
+struct C : B {};
+struct D : virtual A, C {};
+
+__attribute__((noipa)) A *
+baz (C *p, D *q)
+{
+  if (p)
+    return dynamic_cast <A *> (p);
+  else
+    return dynamic_cast <A *> (q);
+}
+
+void
+foo ()
+{ 
+  C c;
+  c.a = 42;
+  __builtin_clear_padding (&c);
+  A *p = baz (&c, 0);
+  if (c.a != 42 || p->a != 42)
+    __builtin_abort ();
+}
+
+void
+bar ()
+{
+  D d;
+  d.a = 42;
+  __builtin_clear_padding (&d);
+  A *p = baz (0, &d);
+  if (d.a != 42 || p->a != 42)
+    __builtin_abort ();
+}
+
+int
+main ()
+{
+  foo ();
+  bar ();
+}