Hi!
When playing with __builtin_bit_cast, I have noticed __builtin_clear_padding
ICE on the G class below. The artificial field with D type has offset 0
and size 8 bytes, but the following artificial field with E type has offset
0 and size 0, so it triggers the asserts that we don't move current position
backwards. Fixed by ignoring is_empty_type (TREE_TYPE (field)) fields, all
of their bits are padding which is what is added when skipping over to next
field anyway.
Ok for trunk if it passes bootstrap/regtest? So far passed all
builtin-clear-padding* tests, so everything that uses these functions ATM
in the GCC tree.
2020-11-26 Jakub Jelinek <ja...@redhat.com>
PR libstdc++/88101
* gimple-fold.c (clear_padding_type): Ignore fields with is_empty_type
types.
* g++.dg/torture/builtin-clear-padding-3.C: New test.
--- gcc/gimple-fold.c.jj 2020-11-26 14:05:07.393268700 +0100
+++ gcc/gimple-fold.c 2020-11-26 14:18:10.826532574 +0100
@@ -4533,6 +4533,8 @@ clear_padding_type (clear_padding_struct
"well defined padding bits for %qs",
field, "__builtin_clear_padding");
}
+ else if (is_empty_type (TREE_TYPE (field)))
+ continue;
else
{
HOST_WIDE_INT pos = int_byte_position (field);
--- gcc/testsuite/g++.dg/torture/builtin-clear-padding-3.C.jj 2020-11-26
14:26:40.532848182 +0100
+++ gcc/testsuite/g++.dg/torture/builtin-clear-padding-3.C 2020-11-26
14:27:51.995051122 +0100
@@ -0,0 +1,24 @@
+/* PR libstdc++/88101 */
+
+struct D { int a; int : 24; int b : 8; };
+struct E {};
+struct F { char c, d, e; };
+struct G : public D, E, F { int f; } g1, g2;
+
+__attribute__((noipa)) void
+foo (G *g)
+{
+ g->a = -1; g->b = -1; g->c = -1; g->d = -1; g->e = -1; g->f = -1;
+}
+
+int
+main ()
+{
+ __builtin_memset (&g2, -1, sizeof (g2));
+ foo (&g1);
+ foo (&g2);
+ __builtin_clear_padding (&g2);
+ if (__builtin_memcmp (&g1, &g2, sizeof (g1)))
+ __builtin_abort ();
+ return 0;
+}
Jakub
