On Mon, Sep 16, 2019 at 12:33:28AM -0400, Jason Merrill wrote:
> Here, if cp_perform_integral_promotions saw that the TREE_TYPE of a
> bit-field reference was the same as the type it promotes to, it didn't do
> anything. But then decay_conversion saw that the bit-field reference was
> unchanged, and converted it to its declared type. So I needed to add
> something to make it clear that promotion has been done. But then the 33819
> change caused trouble by looking through the NOP_EXPR I just added. This
> was the wrong fix for that bug; I've now fixed that better by recognizing in
> cp_perform_integral_promotions that we won't promote a bit-field larger than
> 32 bits, so we should use the declared type.
>
> Tested x86_64-pc-linux-gnu, applying to trunk.
>
> PR c++/33819 - long bit-field promotion.
> * typeck.c (cp_perform_integral_promotions): Handle large bit-fields
> properly. Handle 32-bit non-int bit-fields properly.
> (is_bitfield_expr_with_lowered_type): Don't look through NOP_EXPR.
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/expr/bitfield14.C
> @@ -0,0 +1,17 @@
> +// PR c++/30277
> +// { dg-do compile { target c++11 } }
> +
> +struct S
> +{
> + signed long l: 32;
> +};
> +
> +void foo(long) = delete;
> +void foo(int) {}
> +
> +int main()
> +{
> + S x = {1};
> + foo(x.l+0);
> + return 0;
> +}
This testcase fails on all targets where int and long have the same
precision. Is that a bug on the compiler side, or should the testcase just
use a type with a larger precision than int (i.e. long long), like following
(tested on x86_64-linux and i686-linux):
2019-09-21 Jakub Jelinek <ja...@redhat.com>
PR c++/30277
* g++.dg/expr/bitfield14.C (struct S): Use signed long long instead
of signed long.
(foo): Use long long instead of long.
--- gcc/testsuite/g++.dg/expr/bitfield14.C.jj 2019-09-20 12:25:24.833748976
+0200
+++ gcc/testsuite/g++.dg/expr/bitfield14.C 2019-09-21 08:17:18.500234760
+0200
@@ -3,10 +3,10 @@
struct S
{
- signed long l: 32;
+ signed long long l: 32;
};
-void foo(long) = delete;
+void foo(long long) = delete;
void foo(int) {}
int main()
Jakub
