On 8/24/20 1:40 PM, Jakub Jelinek wrote:
On Mon, Aug 24, 2020 at 02:56:55PM +0200, Mark Wielaard wrote:
In DWARF5 class variables (static data members) are represented with a
DW_TAG_variable instead of a DW_TAG_member. Make sure the variable isn't
optimized away in the constexpr-var-1.C testcase so we can still match (2)
const_expr in the the assembly output.
Note that the same issue causes some failures in the gdb testsuite
for static data members when we enable DWARF5 by default:
https://sourceware.org/bugzilla/show_bug.cgi?id=26525
---
gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C | 1 +
1 file changed, 1 insertion(+)
diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C
b/gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C
index 19062e29fd59..c6ad3f645379 100644
--- a/gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C
+++ b/gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C
@@ -7,3 +7,4 @@ struct S
{
static constexpr int b = 6;
} s;
+const int &c = s.b;
This looks incorrect to me, that is a workaround for a real GCC bug.
Shouldn't we instead do something like (untested) following patch?
I mean, for DWARF < 5 the static data members were using DW_TAG_member,
which has been always marked by the function, so IMHO we should also always
mark the DW_TAG_variables at the class scope that replaced those.
The earlier behavior seems like an accident, that happened because we
always need to emit information about non-static data members. I don't
think we should take it as guidance.
In this case one reason we don't emit debug info is because (before
C++17) there's no definition of 'b'. After C++17 the in-class
declaration of 'b' is a definition, but we don't have to give it a
symbol, so there's still nothing for the debug info to describe.
This issue doesn't seem specific to class members; it also affects
namespace-scope C++17 inline variables:
inline const int var = 42;
int main() { return var; }
Compiling this testcase with -g doesn't emit any debug info for 'var'
even though it's used.
Should we assume that if a variable with DW_AT_const_value is TREE_USED,
we need to write out debug info for it?
Jason
2020-08-24 Jakub Jelinek <ja...@redhat.com>
* dwarf2out.c (prune_unused_types_walk): Mark DW_TAG_variable DIEs
at class scope for DWARF5+.
--- gcc/dwarf2out.c.jj 2020-07-28 15:39:09.883757946 +0200
+++ gcc/dwarf2out.c 2020-08-24 19:33:16.503961786 +0200
@@ -29392,6 +29392,13 @@ prune_unused_types_walk (dw_die_ref die)
if (die->die_perennial_p)
break;
+ /* For static data members, the declaration in the class is supposed
+ to have DW_TAG_member tag in DWARF{3,4} but DW_TAG_variable in
+ DWARF5. DW_TAG_member will be marked, so mark even such
+ DW_TAG_variables in DWARF5. */
+ if (dwarf_version >= 5 && class_scope_p (die->die_parent))
+ break;
+
/* premark_used_variables marks external variables --- don't mark
them here. But function-local externals are always considered
used. */
Jakub
